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1.
Mol Cell ; 8(3): 601-11, 2001 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-11583622

RESUMO

Bid plays an essential role in Fas-mediated apoptosis of the so-called type II cells. In these cells, following cleavage by caspase 8, the C-terminal fragment of Bid translocates to mitochondria and triggers the release of apoptogenic factors, thereby inducing cell death. Here we report that Bid is phosphorylated by casein kinase I (CKI) and casein kinase II (CKII). Inhibition of CKI and CKII accelerated Fas-mediated apoptosis and Bid cleavage, whereas hyperactivity of the kinases delayed apoptosis. When phosphorylated, Bid was insensitive to caspase 8 cleavage in vitro. Moreover, a mutant of Bid that cannot be phosphorylated was found to be more toxic than wild-type Bid. Together, these data indicate that phosphorylation of Bid represents a new mechanism whereby cells control apoptosis.


Assuntos
Apoptose/fisiologia , Proteínas de Transporte/metabolismo , Caspases/metabolismo , Proteínas Quinases/metabolismo , Proteínas Serina-Treonina Quinases/metabolismo , Sequência de Aminoácidos , Animais , Proteína Agonista de Morte Celular de Domínio Interatuante com BH3 , Proteínas de Transporte/genética , Caseína Quinase II , Caseína Quinases , Caspase 8 , Caspase 9 , Fracionamento Celular , Linhagem Celular , Proteínas de Ligação a DNA/metabolismo , Granzimas , Humanos , Immunoblotting , Camundongos , Dados de Sequência Molecular , Fosforilação , Inibidores de Proteínas Quinases , Proteínas Quinases/isolamento & purificação , Proteínas Serina-Treonina Quinases/antagonistas & inibidores , Estrutura Terciária de Proteína , Proteínas Proto-Oncogênicas c-bcl-2/metabolismo , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Serina Endopeptidases/metabolismo , Receptor fas/metabolismo
2.
J Biol Chem ; 276(24): 20882-9, 2001 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-11287424

RESUMO

Aggretin, a potent platelet activator, was isolated from Calloselasma rhodostoma venom, and 30-amino acid N-terminal sequences of both subunits were determined. Aggretin belongs to the heterodimeric snake C-type lectin family and is thought to activate platelets by binding to platelet glycoprotein alpha(2)beta(1). We now show that binding to glycoprotein (GP) Ib is also required. Aggretin-induced platelet activation was inhibited by a monoclonal antibody to GPIb as well as by antibodies to alpha(2)beta(1). Binding of both of these platelet receptors to aggretin was confirmed by affinity chromatography. No binding of other major platelet membrane glycoproteins, in particular GPVI, to aggretin was detected. Aggretin also activates platelets from Fc receptor gamma chain (Fcgamma)-deficient mice to a greater extent than those from normal control mice, showing that it does not use the GPVI/Fcgamma pathway. Platelets from Fcgamma-deficient mice expressed fibrinogen receptors normally in response to collagen, although they did not aggregate, indicating that these platelets may partly compensate via other receptors including alpha(2)beta(1) or GPIb for the lack of the Fcgamma pathway. Signaling by aggretin involves a dose-dependent lag phase followed by rapid tyrosine phosphorylation of a number of proteins. Among these are p72(SYK), p125(FAK), and PLCgamma2, whereas, in comparison with collagen and convulxin, the Fcgamma subunit neither is phosphorylated nor coprecipitates with p72(SYK). This supports an independent, GPIb- and integrin-based pathway for activation of p72(SYK) not involving the Fcgamma receptor.


Assuntos
Plaquetas/fisiologia , Precursores Enzimáticos/sangue , Integrinas/sangue , Integrinas/fisiologia , Isoenzimas/sangue , Lectinas Tipo C , Lectinas/farmacologia , Ativação Plaquetária/fisiologia , Complexo Glicoproteico GPIb-IX de Plaquetas/fisiologia , Proteínas Tirosina Quinases/sangue , Fosfolipases Tipo C/sangue , Venenos de Víboras/química , Venenos de Víboras/farmacologia , Agkistrodon , Sequência de Aminoácidos , Animais , Plaquetas/efeitos dos fármacos , Cromatografia de Afinidade , Colágeno/farmacologia , Venenos de Crotalídeos/farmacologia , Humanos , Técnicas In Vitro , Peptídeos e Proteínas de Sinalização Intracelular , Lectinas/química , Camundongos , Camundongos Endogâmicos C57BL , Dados de Sequência Molecular , Fosfolipase C gama , Fosforilação , Fosfotirosina/sangue , Ativação Plaquetária/efeitos dos fármacos , Complexo Glicoproteico GPIb-IX de Plaquetas/efeitos dos fármacos , Subunidades Proteicas , Receptores de Colágeno , Alinhamento de Sequência , Homologia de Sequência de Aminoácidos , Quinase Syk , Venenos de Víboras/isolamento & purificação
3.
Thromb Haemost ; 86(5): 1277-83, 2001 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-11816718

RESUMO

A new snake protein, named bilinexin, has been purified from Agkistrodon bilineatus venom by ion-exchange chromatography and gel filtration chromatography. Under non-reducing conditions it has a mass of 110 kDa protein on SDS-PAGE. On reduction, it can be separated into five subunits with masses in the range 13-25 kDa. The N-terminal sequences of these subunits are very similar to those of convulxin or the alboaggregins, identifying bilinexin as a new member of the snake C-type lectin family, unusual in having multiple subunits. Bilinexin agglutinates fixed platelets. washed platelets and platelet rich plasma (PRP) without obvious activation (shape change) as confirmed by light microscope examination. Both inhibitory and binding studies indicate that antibodies against alpha2beta1 inhibit not only platelet agglutination induced by bilinexin, but also bilinexin binding to platelets. VM16d, a monoclonal anti-GPIbalpha antibody, completely inhibits platelet agglutination induced by bilinexin, and polyclonal antibodies against GPIbalpha prevent its binding to platelets. However, neither convulxin, polyclonal anti-GPVI antibodies, nor GPIIb/IIIa inhibitors affect its binding to and agglutination of platelets. Bilinexin neither activates GPIIb/IIIa integrin on platelets nor induces tyrosine phosphorylation of platelet proteins, nor increases intracellular Ca2+ in platelets. Like alboaggregin B, bilinexin agglutinates platelets, which makes it a good tool to investigate the differences in mechanism between snake C-type lectins causing platelet agglutination and those that induce full activation.


Assuntos
Plaquetas/efeitos dos fármacos , Venenos de Crotalídeos/metabolismo , Venenos de Crotalídeos/farmacologia , Integrina alfa2beta1/fisiologia , Lectinas Tipo C/metabolismo , Agregação Plaquetária/efeitos dos fármacos , Complexo Glicoproteico GPIb-IX de Plaquetas/fisiologia , Sequência de Aminoácidos , Animais , Anticorpos/farmacologia , Plaquetas/ultraestrutura , Venenos de Crotalídeos/química , Venenos de Crotalídeos/isolamento & purificação , Humanos , Integrina alfa2beta1/imunologia , Lectinas Tipo C/química , Lectinas Tipo C/isolamento & purificação , Peso Molecular , Complexo Glicoproteico GPIb-IX de Plaquetas/imunologia , Subunidades Proteicas
4.
J Biol Chem ; 274(41): 29019-24, 1999 Oct 08.
Artigo em Inglês | MEDLINE | ID: mdl-10506151

RESUMO

We have cloned the platelet collagen receptor glycoprotein (GP) VI from a human bone marrow cDNA library using rapid amplification of cDNA ends with platelet mRNA to complete the 5' end sequence. GPVI was isolated from platelets using affinity chromatography on the snake C-type lectin, convulxin, as a critical step. Internal peptide sequences were obtained, and degenerate primers were designed to amplify a fragment of the GPVI cDNA, which was then used as a probe to screen the library. Purified GPVI, as well as Fab fragments of polyclonal antibodies made against the receptor, inhibited collagen-induced platelet aggregation. The GPVI receptor cDNA has an open reading frame of 1017 base pairs coding for a protein of 339 amino acids including a putative 23-amino acid signal sequence and a 19-amino acid transmembrane domain between residues 247 and 265. GPVI belongs to the immunoglobulin superfamily, and its sequence is closely related to FcalphaR and to the natural killer receptors. Its extracellular chain has two Ig-C2-like domains formed by disulfide bridges. An arginine residue is found in position 3 of the transmembrane portion, which should permit association with Fcgamma and its immunoreceptor tyrosine-based activation motif via a salt bridge. With 51 amino acids, the cytoplasmic tail is relatively long and shows little homology to the C-terminal part of the other family members. The ability of the cloned GPVI cDNA to code for a functional platelet collagen receptor was demonstrated in the megakaryocytic cell line Dami. Dami cells transfected with GPVI cDNA mobilized intracellular Ca(2+) in response to collagen, unlike the nontransfected or mock transfected Dami cells, which do not respond to collagen.


Assuntos
Integrinas/genética , Lectinas Tipo C , Glicoproteínas da Membrana de Plaquetas/genética , Sequência de Aminoácidos , Sequência de Bases , Cálcio/metabolismo , Linhagem Celular , Clonagem Molecular , Venenos de Crotalídeos/metabolismo , Humanos , Fragmentos Fab das Imunoglobulinas/imunologia , Integrinas/química , Dados de Sequência Molecular , Agregação Plaquetária , Glicoproteínas da Membrana de Plaquetas/química , Receptores de Colágeno , Alinhamento de Sequência , Transfecção
5.
Curr Genet ; 36(1-2): 21-8, 1999 Aug.
Artigo em Inglês | MEDLINE | ID: mdl-10447591

RESUMO

Two pro-apoptotic proteases, caspase-1 and caspase-3, have been expressed as full-length proteins in the fission yeast Schizosaccharomyces pombe. Both proteins autoprocess to generate the corresponding active enzyme and both are lethal to the yeast cell. Lethality is due to catalytic activity since the expression of the inactive mutant forms of both caspases does not result in an obvious phenotype. Caspase-expressing yeast can be rescued by co-expression of the baculovirus protein p35, a known inhibitor of the caspase family. Co-expression of Bcl-2, another anti-apoptotic protein, does not prevent the cell death induced by either caspase. However, Bcl-2 is itself cleaved by both caspase-1 and caspase-3 at two adjacent recognition sites, YEWD(31')A and DAGD(34')V respectively, immediately downstream from the N-terminal BH4 domain, a region of Bcl-2 which is essential for its anti-apoptotic activity; similar cleavage of Bcl-2 by caspases has been demonstrated in mammalian cells. Hence, key elements of the apoptotic pathway can be reliably reconstituted in fission yeast, opening the way to exploit yeast in order to study the control of apoptosis. Furthermore, the activity of caspase-3, although not caspase-1, can be demonstrated in vitro using chromogenic substrates. This offers the possibility of using caspase-producing strains of yeast to screen for chemical inhibitors either in vivo or in vitro.


Assuntos
Apoptose , Caspases/metabolismo , Schizosaccharomyces/enzimologia , Transdução de Sinais , Sequência de Aminoácidos , Substituição de Aminoácidos , Sítios de Ligação , Caspase 1/genética , Caspase 1/metabolismo , Caspase 3 , Inibidores de Caspase , Caspases/genética , Cisteína/genética , Cisteína/metabolismo , Expressão Gênica , Genes Letais/genética , Humanos , Proteínas Inibidoras de Apoptose , Mutação , Fragmentos de Peptídeos/química , Fragmentos de Peptídeos/metabolismo , Fenótipo , Proteínas Proto-Oncogênicas c-bcl-2/química , Proteínas Proto-Oncogênicas c-bcl-2/genética , Proteínas Proto-Oncogênicas c-bcl-2/metabolismo , Schizosaccharomyces/citologia , Schizosaccharomyces/genética , Schizosaccharomyces/crescimento & desenvolvimento , Fatores de Tempo , Proteínas Virais/genética , Proteínas Virais/metabolismo
6.
Protein Expr Purif ; 15(2): 202-6, 1999 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-10049676

RESUMO

Bax is a proapoptotic ion channel forming protein of the Bcl-2 family. In cells the protein is found in the cytosol and in the mitochondria membrane where it presumably is involved during apoptosis in disruption of the mitochondrial membrane potential and release of cytochrome c. The protein has a hydrophobic domain at the C-terminus, which renders it a limited solubility. Thus, all studies on recombinant Bax has so far been performed on C-terminal truncated protein. We have expressed and purified the full-length human Bax alpha. The protein was expressed with a His tag at the N-terminus and purified by affinity chromatography on Ni-NTA-agarose followed by ion-exchange chromatography on Q-Sepharose. The protein was more than 98% pure on SDS-PAGE and in the presence of 1% (w/v) octyl glucoside it could be concentrated up to 0.5 mg/ml. Full-length Bax was 25-fold more efficient, compared to C-terminal truncated Bax, in forming ion channels and trigger carboxyfluorescein release from liposomes.


Assuntos
Proteínas Proto-Oncogênicas c-bcl-2 , Proteínas Proto-Oncogênicas/isolamento & purificação , Sequência de Aminoácidos , Apoptose/genética , Sequência de Bases , Cromatografia de Afinidade , Cromatografia por Troca Iônica , Escherichia coli , Fluoresceínas , Corantes Fluorescentes , Vetores Genéticos/genética , Humanos , Canais Iônicos/metabolismo , Lipossomos , Dados de Sequência Molecular , Fragmentos de Peptídeos/biossíntese , Fragmentos de Peptídeos/isolamento & purificação , Fragmentos de Peptídeos/farmacologia , Proteínas Proto-Oncogênicas/biossíntese , Proteínas Proto-Oncogênicas/genética , Proteínas Proto-Oncogênicas/farmacologia , Proteínas Recombinantes de Fusão/biossíntese , Proteínas Recombinantes de Fusão/isolamento & purificação , Proteínas Recombinantes de Fusão/farmacologia , Solubilidade , Proteína X Associada a bcl-2
7.
Thromb Haemost ; 80(4): 645-8, 1998 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-9798985

RESUMO

Glycoprotein Ia* (GPIa*), a very high molecular mass, platelet alpha-granule protein consisting of 167 kDa subunits disulphide-linked in a multimeric structure, was first described by Bienz and Clemetson in 1989 (J. Biol. Chem. 264, 507-514). In 1991 Hayward et al. (J. Biol. Chem. 266, 7114-7120) independently identified a platelet protein with multimeric structure. Despite strong similarities to GPIa* they concluded that it was a novel multimeric protein and named it first p-155 and later, multimerin. Multimerin has also been found in endothelial cells and has been cloned recently from an endothelial cell cDNA library. This has made it possible for us to clarify the relationship between GPIa* and multimerin. GPIa* was isolated from platelet releasate and the N-terminal sequence of 167 kDa and 155 kDa subunit species were determined. The N-terminal 15 amino acids of GPIa* were identical to the deduced amino acids 184-198 of endothelial multimerin. The N-terminal sequence of the 155 kDa protein was identical to the deduced amino acids 318-326 of multimerin. Thus, platelet GPIa* (167 kDa) is the main processed form of multimerin stored in platelet alpha-granules. The GPIa*/processed multimerin (167 kDa) still contains an RGDS sequence near its N-terminus as well as an EGF domain which may be involved in binding to the platelet surface after release. This sequence and domain are cleaved off in the p-155 form, described earlier as platelet multimerin, which is probably formed after release from alpha-granules.


Assuntos
Antígenos CD/metabolismo , Plaquetas/metabolismo , Proteínas Sanguíneas/metabolismo , Integrinas/metabolismo , Sequência de Aminoácidos , Antígenos CD/química , Antígenos CD/genética , Plaquetas/ultraestrutura , Proteínas Sanguíneas/química , Proteínas Sanguíneas/genética , Grânulos Citoplasmáticos/metabolismo , Humanos , Integrina alfa2 , Integrinas/química , Integrinas/genética , Dados de Sequência Molecular , Processamento de Proteína Pós-Traducional , Receptores de Colágeno , Análise de Sequência
8.
J Biol Chem ; 272(40): 25238-42, 1997 Oct 03.
Artigo em Inglês | MEDLINE | ID: mdl-9312139

RESUMO

We have studied the phosphorylation of the Bcl-2 family of proteins by different mitogen-activated protein (MAP) kinases. Purified Bcl-2 was found to be phosphorylated by the c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK) p54-SAPKbeta, and this is specific insofar as the extracellular signal-regulated kinase 1 (ERK1) and p38/RK/CSBP (p38) catalyzed only weak modification. Bcl-2 undergoes similar phosphorylation in COS-7 when coexpressed together with p54-SAPKbeta and the constitutive Rac1 mutant G12V. This is seen by both 32PO4 labeling and the appearance of five discrete Bcl-2 bands with reduced gel mobility. As anticipated, both intracellular p54-SAPKbeta activation and Bcl-2 phosphorylation are blocked by co-transfection with the MAP kinase specific phosphatase MKP3/PYST1. MAP kinase specificity is also seen in COS-7 cells as Bcl-2 undergoes only weak phosphorylation when co-expressed with enzymatically activated ERK1 or p38. Four critical residues undergoing phosphorylation in COS-7 cells were identified by expression of the quadruple Bcl-2 point mutant T56A,S70A,T74A, S87A. Sequencing phosphopeptides derived from tryptic digests of Bcl-2 indicates that purified GST-p54-SAPKbeta phosphorylates identical sites in vitro. This is the first report of Bcl-2 phosphorylation by the JNK/SAPK class of MAP kinases and could indicate a key modification allowing control of Bcl-2 function by cell surface receptors, Rho family GTPases, and/or cellular stresses.


Assuntos
Proteínas Quinases Dependentes de Cálcio-Calmodulina/metabolismo , Proteínas de Ligação ao GTP/metabolismo , Proteínas Quinases Ativadas por Mitógeno , Proteínas Serina-Treonina Quinases/metabolismo , Proteínas Tirosina Quinases/metabolismo , Proteínas Proto-Oncogênicas c-bcl-2/química , Proteínas Proto-Oncogênicas c-bcl-2/metabolismo , Sequência de Aminoácidos , Animais , Sequência de Bases , Células COS , Primers do DNA , Ativação Enzimática , Guanosina Trifosfato/metabolismo , Proteínas Quinases JNK Ativadas por Mitógeno , Proteína Quinase 10 Ativada por Mitógeno , Dados de Sequência Molecular , Mutagênese Sítio-Dirigida , Fragmentos de Peptídeos/química , Fosfopeptídeos/química , Fosforilação , Mutação Puntual , Reação em Cadeia da Polimerase , Estrutura Secundária de Proteína , Proteínas Recombinantes/metabolismo , Deleção de Sequência , Transfecção , Proteínas rac de Ligação ao GTP
9.
J Biol Chem ; 272(21): 13576-83, 1997 May 23.
Artigo em Inglês | MEDLINE | ID: mdl-9153205

RESUMO

Convulxin, a powerful platelet activator, was isolated from Crotalus durissus terrificus venom, and 20 amino acid N-terminal sequences of both subunits were determined. These indicated that convulxin belongs to the heterodimeric C-type lectin family. Neither antibodies against GPIb nor echicetin had any effect on convulxin-induced platelet aggregation showing that, in contrast to other venom C-type lectins acting on platelets, GPIb is not involved in convulxin-induced platelet activation. In addition, partially reduced/denatured convulxin only affects collagen-induced platelet aggregation. The mechanism of convulxin-induced platelet activation was examined by platelet aggregation, detection of time-dependent tyrosine phosphorylation of platelet proteins, and binding studies with 125I-convulxin. Convulxin induces signal transduction in part like collagen, involving the time-dependent tyrosine phosphorylation of Fc receptor gamma chain, phospholipase Cgamma2, p72(SYK), c-Cbl, and p36-38. However, unlike collagen, pp125(FAK) and some other bands are not tyrosine-phosphorylated. Convulxin binds to a glycosylated 62-kDa membrane component in platelet lysate and to p62/GPVI immunoprecipitated by human anti-p62/GPVI antibodies. Convulxin subunits inhibit both aggregation and tyrosine phosphorylation in response to collagen. Piceatannol, a tyrosine kinase inhibitor with some specificity for p72(SYK), showed differential effects on collagen and convulxin-stimulated signaling. These results suggest that convulxin uses the p62/GPVI but not the alpha2beta1 part of the collagen signaling pathways to activate platelets. Occupation and clustering of p62/GPVI may activate Src family kinases phosphorylating Fc receptor gamma chain and, by a mechanism previously described in T- and B-cells, activate p72(SYK) that is critical for downstream activation of platelets.


Assuntos
Venenos de Crotalídeos/farmacologia , Lectinas Tipo C , Ativação Plaquetária/efeitos dos fármacos , Glicoproteínas da Membrana de Plaquetas/metabolismo , Transdução de Sinais/efeitos dos fármacos , Sequência de Aminoácidos , Animais , Proteínas de Transporte/metabolismo , Cromatografia Líquida de Alta Pressão , Colágeno/farmacologia , Venenos de Crotalídeos/química , Crotalus , Humanos , Integrinas/metabolismo , Dados de Sequência Molecular , Fosforilação , Agregação Plaquetária/efeitos dos fármacos , Inibidores da Agregação Plaquetária/farmacologia , Complexo Glicoproteico GPIb-IX de Plaquetas/metabolismo , Ligação Proteica , Desnaturação Proteica , Receptores de Colágeno , Estilbenos/farmacologia , Tirosina/metabolismo
10.
Biochem J ; 323 ( Pt 2): 533-7, 1997 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-9163349

RESUMO

Echicetin, a heterodimeric protein from the venom of Echis carinatus, binds to platelet glycoprotein Ib (GPIb) and so inhibits platelet aggregation or agglutination induced by various platelet agonists acting via GPIb. The amino acid sequence of the beta subunit of echicetin has been reported and found to belong to the recently identified snake venom subclass of the C-type lectin protein family. Echicetin alpha and beta subunits were purified. N-terminal sequence analysis provided direct evidence that the protein purified was echicetin. The paper presents the complete amino acid sequence of the alpha subunit and computer models of the alpha and beta subunits. The sequence of alpha echicetin is highly similar to the alpha and beta chains of various heterodimeric and homodimeric C-type lectins. Neither of the fully reduced and alkylated alpha or beta subunits of echicetin inhibited the platelet agglutination induced by von Willebrand factor-ristocetin or alpha-thrombin. Earlier reports about the inhibitory activity of reduced and alkylated echicetin beta subunit might have been due to partial reduction of the protein.


Assuntos
Simulação por Computador , Modelos Moleculares , Proteínas/química , Venenos de Víboras/química , Sequência de Aminoácidos , Animais , Proteínas de Transporte , Espectrometria de Massas , Dados de Sequência Molecular , Conformação Proteica , Viperidae
11.
Protein Expr Purif ; 9(1): 61-8, 1997 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-9116503

RESUMO

Escherichia coli remains an organism of choice for the production of recombinant proteins required in large quantities. Whenever possible, secretion is the preferred strategy since it permits easy and efficient purification from the extracellular medium. Our efforts to use E. coli to secrete a human CD23 soluble variant fused to a pair of IgG binding domains via the Staphylococcal protein A signal peptide were unsuccessful. Surprisingly, when the same construct was expressed in the baculovirus system, efficient secretion was observed and cleavage of the signal peptide occurred at the expected site. Varying the genes in the fusions or the tags, or the topology of the gene and the tag, did not affect the high-level secretion and cleavage at the correct site. We envision that fusion of the bacterial signal sequence to eukaryotic recombinant genes will prove to be a tool of value for efficient protein secretion in insect cells using the baculovirus expression system.


Assuntos
Baculoviridae/genética , Sinais Direcionadores de Proteínas/genética , Receptores de IgE/genética , Proteínas Recombinantes de Fusão/metabolismo , Proteína Estafilocócica A/genética , Sequência de Aminoácidos , Animais , Transporte Biológico , Compartimento Celular , Retículo Endoplasmático , Células Eucarióticas , Humanos , Camundongos , Dados de Sequência Molecular , Células Procarióticas , Engenharia de Proteínas/métodos , Spodoptera/citologia , Spodoptera/virologia
12.
Biochem J ; 319 ( Pt 3): 961-8, 1996 Nov 01.
Artigo em Inglês | MEDLINE | ID: mdl-8921006

RESUMO

Several studies have shown that Asp-49 is the residue that controls calcium binding in, and so plays a critical role in the calcium-mediated activation of, low-M(r) group I-III phospholipases A2 (PLA2s). The present paper provides experimental evidence that Asp-49 is not an absolute prerequisite for the enzymic activity of PLA2s, and that proteins with amino acid(s) other than Asp at position 49 can exhibit significant phospholipase activity. The purification, complete amino acid sequence and characterization of ecarpholin S, a PLA2 from Echis carinatus sochureki (saw-scaled viper) venom, is described. This single-chain, 122-amino-acid, basic (pI 7.9) protein is a group II PLA2. Although Asp-49 is replaced by Ser and Tyr-28 by Phe (both of these positions being involved in the Ca(2+)-binding site of PLA2s), the lipolysis of soybean phosphatidylcholine and egg yolk in the presence of 10 mM CaCl2 was 1.5 times and 2.9 times greater respectively with ecarpholin S than with recombinant human group II PLA2. The Ca(2+)-dependencies of the enzymic activities of ecarpholin S and rPLA2 were found to be similar. Ecarpholin S added to washed platelets induced aggregation; the presence of Ca2+ was a prerequisite for this platelet-aggregating effect. Computer modelling of the Ca(2+)-binding site of Ser-49 PLA2 compared with the Asp-49 and Lys-49 forms, for which crystallographic data exist, shows that the Ca(2+)-binding site is sterically blocked by Lys-49 but not by Ser-49; in the latter, the Ser hydroxy group may replace the Asp carboxylate in stabilization of Ca2+ binding. Sequence comparisons of ecarpholin S and other low-M(r) PLA2s predicts the presence of a Ser-49 group in the protein family of low-M(r) PLA2s that is distinct from the Asp-49 and Lys-49 groups.


Assuntos
Ácido Aspártico , Fosfolipases A/química , Fosfolipases A/metabolismo , Conformação Proteica , Serina , Venenos de Víboras/química , Venenos de Víboras/metabolismo , Sequência de Aminoácidos , Animais , Sítios de Ligação , Simulação por Computador , Fosfolipases A2 do Grupo II , Humanos , Cinética , Modelos Moleculares , Dados de Sequência Molecular , Fosfolipases A/isolamento & purificação , Fosfolipases A2 , Proteínas Recombinantes/química , Proteínas Recombinantes/isolamento & purificação , Proteínas Recombinantes/metabolismo , Proteínas de Répteis , Homologia de Sequência de Aminoácidos , Venenos de Víboras/isolamento & purificação , Viperidae
13.
Eur J Biochem ; 228(3): 658-64, 1995 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-7737160

RESUMO

We have purified platelet factor 4 from porcine platelets and shown that it is glycosylated. The purified protein migrated as a broad band at approximately 14,000 Da, characteristic of glycoproteins. Electrospray mass spectroscopy of the intact protein gave a predominant mass of 11,111 Da, with a minor component of 10,804 Da. Sialidase digestion reduces both forms to a single mass of 10,497 Da. Upon Edman degradation, the amino terminus was found to be blocked by the presence of a pyroglutamate residue. We have determined the complete primary structure of platelet factor 4 by peptide mapping and Edman degradation, thereby completing information on the amino-terminal and carboxy-terminal regions which is missing in the previously published partial sequence. Sequencing of the intact and deglycosylated protein show that the glycosylation site is at Thr8. The amino acid composition accounts for a mass of 9623 Da, and the carbohydrate moeity was found to contribute 1490 Da. The biological activity of the porcine protein has been compared to recombinant human platelet factor 4 in an endothelial cell proliferation assay; both inhibit at a concentration giving half the maximal inhibition of 0.1 microM. Removal of the 19 amino-terminal residues carrying the carbohydrate moiety results in no change in the biological activity.


Assuntos
Fator Plaquetário 4/química , Sequência de Aminoácidos , Animais , Divisão Celular/efeitos dos fármacos , Células Cultivadas , Cromatografia Líquida de Alta Pressão , Endotélio Vascular/citologia , Endotélio Vascular/efeitos dos fármacos , Glicosilação , Humanos , Espectrometria de Massas/métodos , Dados de Sequência Molecular , Fator Plaquetário 4/isolamento & purificação , Fator Plaquetário 4/farmacologia , Suínos
14.
Biochemistry ; 33(19): 5777-82, 1994 May 17.
Artigo em Inglês | MEDLINE | ID: mdl-8180205

RESUMO

The reaction catalyzed by Candida albicans phosphomannose isomerase (PMI) (EC 5.3.1.8) has a bell-shaped pH dependence, with pKa's at 5.6 and 8.7. The enzyme can be inhibited in a time-dependent manner using the arginine-specific modification reagent phenylglyoxal. This modification takes place with a rate constant of 0.022 +/- 0.002 min-1 mM-1 at 37 degrees C in 50 mM Hepes buffer, pH 8.5. The enzyme can be protected from this inactivation by the addition of the substrate mannose 6-phosphate at concentrations close to its Km value. The pH dependence of the inactivation reaction shows a single pKa at 9.1 +/- 0.1, which is close to one of the values for the pH dependence of the enzyme-catalyzed reaction. Using [7-14C]phenylglyoxal, it is shown that a single molecule is incorporated into the enzyme in the absence of substrate and that this inactivates the enzyme. This incorporation of radioactivity is prevented by the coincubation with substrate. The modified protein has then been reduced with sodium borohydride to fix the modification and then cleaved with Asp-N protease. The resultant peptides were separated by HPLC, and the radioactivity was counted. Sequencing of the peptide with the highest incorporation level identified it as DNVVRAGFTPKFK, which corresponds to amino acids 300-312 of phosphomannose isomerase. Radioactive counting of the phenylthiohydantoin amino acid derivatives confirmed that the modified amino acid was arginine 304. The role of this residue in the catalytic reaction of phosphomannose isomerase is discussed.


Assuntos
Arginina/metabolismo , Candida albicans/enzimologia , Manose-6-Fosfato Isomerase/metabolismo , Sequência de Aminoácidos , Arginina/análise , Sítios de Ligação , Cromatografia Líquida de Alta Pressão , Cinética , Manose-6-Fosfato Isomerase/antagonistas & inibidores , Manose-6-Fosfato Isomerase/química , Dados de Sequência Molecular , Mapeamento de Peptídeos , Fenilglioxal/farmacologia
15.
Eur J Biochem ; 221(2): 713-9, 1994 Apr 15.
Artigo em Inglês | MEDLINE | ID: mdl-7513641

RESUMO

In our search for novel chemoattractant factors, we have purified a heparin-binding protein from porcine platelets which is a potent chemoattractant for human neutrophils. The protein has 80 amino acids and a molecular mass of 8597.5Da as measured by electrospray mass spectrometry. It has been characterised by amino acid sequencing and shown to have highest identity to members of the human platelet basic-protein-family. Its N-terminal sequence is intermediate in length between the human connective-tissue-activating polypeptide III (CTAP-III) and neutrophil-activating polypeptide-2 (NAP-2). The porcine NAP-2/CTAP-III shows the classic CXC cysteine spacing found towards the N-terminus in the chemokine alpha family and contains the ELR motif which has been shown to be essential for neutrophil chemotaxis. We have isolated mRNA from porcine platelets and constructed a cDNA library containing 1.0 x 10(6) independent clones. Using probes based on the protein sequence we have isolated a full length-clone for this gene, with an open reading frame containing 119 amino acids. Despite overall similarity between the human and porcine proteins, the N-terminal region is almost completely different between the two species, with only two identical amino acids. The proteolytic cleavage sites required for processing of human platelet basic protein are completely missing in the porcine homologue, implying a different processing pathway or mechanism. The porcine protein is capable of agonizing certain effects of both NAP-2 and CTAP-III when incubated with human cells indicating that the same porcine protein may be involved in both processes.


Assuntos
Fatores de Coagulação Sanguínea/química , Plaquetas/química , Fatores Quimiotáticos/química , Peptídeos/química , Sequência de Aminoácidos , Animais , Sequência de Bases , Fatores de Coagulação Sanguínea/genética , Fatores de Coagulação Sanguínea/isolamento & purificação , Fatores de Coagulação Sanguínea/farmacologia , Fatores Quimiotáticos/genética , Fatores Quimiotáticos/isolamento & purificação , Fatores Quimiotáticos/farmacologia , Quimiotaxia de Leucócito , Clonagem Molecular , DNA Complementar , Liberação de Histamina , Humanos , Dados de Sequência Molecular , Peso Molecular , Neutrófilos/efeitos dos fármacos , Neutrófilos/fisiologia , Peptídeos/genética , Peptídeos/isolamento & purificação , Peptídeos/farmacologia , Reação em Cadeia da Polimerase , Suínos , beta-Tromboglobulina
16.
Biochemistry ; 32(51): 14139-44, 1993 Dec 28.
Artigo em Inglês | MEDLINE | ID: mdl-8260497

RESUMO

Candida albicans phosphomannose isomerase (PMI) (EC 5.3.1.8) has been recently cloned and overexpressed in Escherichia coli. The enzyme can be irreversibly inactivated by iodoacetate in 50 mM borate buffer, pH 9.0, in a time-dependent manner at a rate of 4.2 +/- 0.03 min-1 M-1. This inhibition can be prevented by the substrate mannose 6-phosphate with a Ks of 0.22 +/- 0.05 mM, slightly lower than its Km value. However, metals such as zinc and cadmium, which are reversible, competitive inhibitors for PMI, do not protect the enzyme against modification. The protein has been labeled by using [2-14C]iodoacetate, in the presence or absence of substrate, and the protein is fully inactivated when 1.0 thiol group is modified per molecule of enzyme. Tryptic maps of the modified protein have been produced. The protected peptide has been identified and sequenced, and the phenylthiohydantoin amino acids have been collected. The modified amino acid is Cys-150. This cysteine residue is conserved in mammalian and yeast phosphomannose isomerases, but not in bacterial species where it is replaced with asparagine. We therefore purified PMI from E. coli and showed that this enzyme is not sensitive to inactivation by iodoacetate. The iodoacetate is presumably inhibiting PMI by sterically blocking the mannose 6-phosphate binding site. Multiple sequence alignment procedures were used to try to identify potential ligands of the zinc atom that is essential for enzyme activity and thus to delineate the active site region.(ABSTRACT TRUNCATED AT 250 WORDS)


Assuntos
Candida albicans/enzimologia , Cisteína/química , Manose-6-Fosfato Isomerase/química , Sequência de Aminoácidos , Sítios de Ligação , Catálise , Proteínas Fúngicas/química , Iodoacetatos/farmacologia , Ácido Iodoacético , Cinética , Manose-6-Fosfato Isomerase/antagonistas & inibidores , Metaloproteínas/química , Dados de Sequência Molecular , Fragmentos de Peptídeos/química , Zinco/química
17.
Biochem J ; 286 ( Pt 3): 819-24, 1992 Sep 15.
Artigo em Inglês | MEDLINE | ID: mdl-1417742

RESUMO

The purification to homogeneity of an active soluble 25 kDa fragment of CD23, produced in insect cells using the baculovirus expression system, is described. Peptide mapping and analysis by Edman degradation and mass spectrometry permitted partial characterization of the protein. A total of 165 out of 172 residues, including N-terminal and C-terminal regions, were mapped. The positions of the two disulphide bonds in the IgE-binding region were also determined: residue 110 is joined to residue 124, and residue 42 to residue 133. Natural CD23 25 kDa fragment was also analysed and found to possess the same disulphide bond arrangement. These results extend the previously noted sequence similarity with lectins to elements of secondary structure.


Assuntos
Receptores de IgE/química , Sequência de Aminoácidos , Cromatografia Líquida de Alta Pressão , Dissulfetos/química , Eletroforese em Gel de Poliacrilamida , Humanos , Imunoglobulina E/metabolismo , Espectrometria de Massas , Dados de Sequência Molecular , Mapeamento de Peptídeos , Receptores de IgE/genética , Receptores de IgE/isolamento & purificação , Proteínas Recombinantes/química , Proteínas Recombinantes/isolamento & purificação , Tripsina
19.
Ann Nutr Aliment ; 32(2-3): 326-38, 1978.
Artigo em Francês | MEDLINE | ID: mdl-707918

RESUMO

The biological availability of amino acids modified by industrial processes has been measured in trials on rats, and their metabolic transit (urinary and faecal excretions, transformation into CO2 and retention in organs) has been studied using molecules labelled with 14C. Maillard reaction products. epsilon-fructose-lysine is not utilized as lysine source. However, less than 10 p. 100 of this substance, bound to proteins, is excreted unmodified in the urine. Intestinal flora destroys most of the fraction which is not absorbed. Premelanoidins are partially absorbed and "burnt" in the organism, whereas high molecularightwe melanoïdins are totally excreted in the faeces. epsilon-(gamma-glutamyl)-lysine and epsilon-(beta-aspartyl)-lysine isopeptides. 80 to 100 p. 100 of free epsilon-(gamma-glutamyl)-lysine are utilized by the Rat. It seems to be absorbed by the intestine, and subsequently hydrolyzed by the kidney, thus releasing lysine. Utilization of this isopeptide bound to proteins has not been shown till now. Free epsilon-(beta-aspartyl)-lysine is not utilized as lysine source. Methionine sulfoxyde and methionine sulfone. Methionine sulfone is not utilized as methionine source whereas most of the free and bound methionine sulfoxide is, in part, it is "reduced" by the liver (perfused liver). Lysino-alanine. Formation of lysino-alanine reduces the availability of lysine and cystine. It is partially excreted in urines, mainly as free lysino-alanine, but also as acetylated derivatives and unknown catabolites.


Assuntos
Aminoácidos/metabolismo , Proteínas Alimentares , Manipulação de Alimentos , Animais , Lisina/metabolismo , Metionina/metabolismo , Ratos
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