RESUMO
Metacaspases are caspase-like homologs which undergo a complex maturation process involving multiple intra-chain cleavages resulting in a composite enzyme made of a p10 and a p20 domain. Their proteolytic activity involving a cysteine-histidine catalytic dyad, show peptide bond cleavage specificity in the C-terminal to lysine and arginine, with both maturation- and catalytic processes being calcium-dependent. Here, we present the structure of a metacaspase from the yeast Candida glabrata, CgMCA-I, in complex with a unique calcium along with a structure in which three magnesium ions are bound. We show that the Ca2+ ion interacts with a loop in the vicinity of the catalytic site. The reorganization of this cation binding loop, by bringing together the two catalytic residues, could be one of the main structural determinants triggering metacaspase activation. Enzymatic exploration of CgMCA-I confirmed that the maturation process implies a trans mechanism with sequential cleavages.
Assuntos
Cálcio , Candida glabrata , Cálcio/metabolismo , Candida glabrata/genética , Caspases/química , Caspases/metabolismo , Lisina/metabolismo , Arginina/químicaRESUMO
TAX2 peptide is a cyclic peptide that acts as an orthosteric antagonist for thrombospondin-1 (TSP-1) interaction with CD47. TAX2 was first described for its anti-angiogenic activities and showed anti-cancer efficacy in numerous preclinical models. Here, we aimed at providing an extensive molecular characterization of TAX2 mode of action, while evaluating its potential in ovarian cancer therapy. Multidisciplinary approaches were used to qualify a TAX2 drug candidate in terms of stability, solubility and potency. Then, efficacy studies, together with benchmark experiments, were performed in relevant mouse models of ovarian carcinoma. TAX2 peptide appears to be stable and soluble in clinically relevant solvents, while displaying a favorable safety profile. Moreover, clinical data mining allowed for the identification of TSP-1 as a relevant pharmacological target in ovarian cancer. In mice, TAX2 therapy inhibits ovarian tumor growth and metastatic dissemination, while activating anti-cancer adaptive immunity. Interestingly, TAX2 also synergizes when administered in combination with anti-PD-1 immune checkpoint inhibitiors. Altogether, our data expose TAX2 as an optimized candidate with advanced preclinical characterization. Using relevant syngeneic ovarian carcinoma models, we highlighted TAX2's ability to convert poorly immunogenic tumors into ones displaying effective anti-tumor T-cell immunity.
RESUMO
Little is known about the structure of the envelope glycoproteins of hepatitis C virus (HCV). To identify new regions essential for the function of these glycoproteins, we generated HCV pseudoparticles (HCVpp) containing HCV envelope glycoproteins, E1 and E2, from different genotypes in order to detect intergenotypic incompatibilities between these two proteins. Several genotype combinations were nonfunctional for HCV entry. Of interest, a combination of E1 from genotype 2a and E2 from genotype 1a was nonfunctional in the HCVpp system. We therefore used this nonfunctional complex and the recently described structural model of E2 to identify new functional regions in E2 by exchanging protein regions between these two genotypes. The functionality of these chimeric envelope proteins in the HCVpp system and/or the cell-cultured infectious virus (HCVcc) was analyzed. We showed that the intergenotypic variable region (IgVR), hypervariable region 2 (HVR2), and another segment in domain II play a role in E1E2 assembly. We also demonstrated intradomain interactions within domain I. Importantly, we also identified a segment (amino acids [aa] 705 to 715 [segment 705-715]) in the stem region of E2, which is essential for HCVcc entry. Circular dichroism and nuclear magnetic resonance structural analyses of the synthetic peptide E2-SC containing this segment revealed the presence of a central amphipathic helix, which likely folds upon membrane binding. Due to its location in the stem region, segment 705-715 is likely involved in the reorganization of the glycoprotein complexes taking place during the fusion process. In conclusion, our study highlights new functional and structural regions in HCV envelope glycoprotein E2.
Assuntos
Hepacivirus/metabolismo , Proteínas do Envelope Viral/química , Proteínas do Envelope Viral/metabolismo , Vírion/metabolismo , Internalização do Vírus , Sequência de Aminoácidos , Linhagem Celular Tumoral , Dicroísmo Circular , Genótipo , Células HEK293 , Hepacivirus/classificação , Hepacivirus/genética , Hepacivirus/fisiologia , Humanos , Modelos Moleculares , Dados de Sequência Molecular , Ressonância Magnética Nuclear Biomolecular , Peptídeos/síntese química , Peptídeos/química , Ligação Proteica , Estrutura Terciária de Proteína , Proteínas Recombinantes de Fusão/química , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Relação Estrutura-Atividade , Proteínas do Envelope Viral/genéticaRESUMO
Peptide microarrays are useful tools for the characterization of humoral responses against peptide antigens. The study of post-translational modifications requires the printing of appropriately modified peptides, whose synthesis can be time-consuming and expensive. We describe here a method named "chips from chips", which allows probing the presence of antibodies directed toward modified peptide antigens starting from unmodified peptide microarrays. The chip from chip concept is based on the modification of peptide microspots by simple chemical reactions. The starting peptide chip (parent chip) is covered by the reagent solution, thereby allowing the modification of specific residues to occur, resulting in the production of a modified peptide chip (daughter chip). Both parent and daughter chips can then be used for interaction studies. The method is illustrated using reductive methylation for converting lysines into dimethyllysines. The rate of methylation was studied using specific antibodies and fluorescence detection, or surface-assisted laser desorption ionization mass spectrometry. This later technique showed unambiguously the efficient methylation of the peptide probes. The method was then used to study the humoral response against the Mycobacterium tuberculosis heparin-binding hemagglutinin, a methylated surface-associated virulence factor and powerful diagnostic and protective antigen.
Assuntos
Espectrometria de Massas/métodos , Análise em Microsséries/métodos , Peptídeos/análise , Proteômica/métodos , Sequência de Aminoácidos , Animais , Anticorpos Antibacterianos/sangue , Feminino , Lectinas/imunologia , Lectinas/metabolismo , Metilação , Camundongos , Camundongos Endogâmicos BALB C , Dados de Sequência Molecular , Mycobacterium tuberculosis/metabolismo , Peptídeos/metabolismo , Proteínas/imunologia , Proteínas/metabolismo , Reprodutibilidade dos TestesRESUMO
Peptide microarrays are useful tools for characterizing the humoral response against methylated antigens. They are usually prepared by printing unmodified and methylated peptides on substrates such as functionalized microscope glass slides. The preferential capture of antibodies by methylated peptides suggests the specific recognition of methylated epitopes. However, unmodified peptide epitopes can be masked due to their interaction with the substrate. The accessibility of unmodified peptides and thus the specificity of the recognition of methylated peptide epitopes can be probed using the in situ methylation procedure described here. Alternately, the in situ methylation of peptide microarrays allows probing the presence of antibodies directed toward methylated epitopes starting from easy-to-make and cost-effective unmodified peptide libraries. In situ methylation was performed using formaldehyde in the presence of sodium cyanoborohydride and nickel chloride. This chemical procedure converts lysine residues into mono- or dimethyl lysines.
Assuntos
Anticorpos/imunologia , Lectinas/química , Lectinas/imunologia , Fragmentos de Peptídeos/química , Análise Serial de Proteínas/métodos , Alquilação , Aminas/química , Sequência de Aminoácidos , Animais , Proteínas de Bactérias/química , Proteínas de Bactérias/imunologia , Boroidretos/química , Formaldeído/química , Vidro/química , Lisina/química , Metilação , Camundongos , Microscopia , Dados de Sequência Molecular , Mycobacterium tuberculosis , Níquel/química , Fragmentos de Peptídeos/imunologia , Fragmentos de Peptídeos/metabolismo , ImpressãoRESUMO
Nonstructural protein 4B (NS4B) plays an essential role in the formation of the hepatitis C virus (HCV) replication complex. It is a relatively poorly characterized integral membrane protein predicted to comprise four transmembrane segments in its central portion. Here, we describe a novel determinant for membrane association represented by amino acids (aa) 40 to 69 in the N-terminal portion of NS4B. This segment was sufficient to target and tightly anchor the green fluorescent protein to cellular membranes, as assessed by fluorescence microscopy as well as membrane extraction and flotation analyses. Circular dichroism and nuclear magnetic resonance structural analyses showed that this segment comprises an amphipathic alpha-helix extending from aa 42 to 66. Attenuated total reflection infrared spectroscopy and glycosylation acceptor site tagging revealed that this amphipathic alpha-helix has the potential to traverse the phospholipid bilayer as a transmembrane segment, likely upon oligomerization. Alanine substitution of the fully conserved aromatic residues on the hydrophobic helix side abrogated membrane association of the segment comprising aa 40 to 69 and disrupted the formation of a functional replication complex. These results provide the first atomic resolution structure of an essential membrane-associated determinant of HCV NS4B.
Assuntos
Membrana Celular/virologia , Hepacivirus/genética , Proteínas não Estruturais Virais/química , Sequência de Aminoácidos , Substituição de Aminoácidos , Linhagem Celular Tumoral , Dicroísmo Circular , Proteínas de Fluorescência Verde/química , Humanos , Espectroscopia de Ressonância Magnética , Modelos Moleculares , Dados de Sequência Molecular , Estrutura Secundária de Proteína , Estrutura Terciária de Proteína , Proteínas Recombinantes de Fusão/química , Alinhamento de Sequência , Espectroscopia de Infravermelho com Transformada de FourierRESUMO
Glyoxylyl-peptides are useful peptide derivatives in the context of hydrazone, oxime or thiazolidine ligations. We describe a method for the determination of glyoxylyl-peptide concentration based on the reaction of the alpha-oxo aldehyde group with an excess of O-benzylhydroxylamine. The amount of O-benzylhydroxylamine necessary to convert the alpha-oxo aldehyde group into the corresponding O-benzyloxime was determined by RP-HPLC analysis and corresponded to the quantity of glyoxylyl-peptide used in the experiment. The method is rapid, sensitive, accurate and allows the automated analysis of several samples.