Characterization of suramin binding sites on the human group IIA secreted phospholipase A2 by site-directed mutagenesis and molecular dynamics simulation.

Suramin is a polysulphonated naphthylurea with inhibitory activity against the human secreted group IIA phospholipase A(2) (hsPLA2GIIA), and we have investigated suramin binding to recombinant hsPLA2GIIA using site-directed mutagenesis and molecular dynamics (MD) simulations. The changes in suramin binding affinity of 13 cationic residue mutants of the hsPLA2GIIA was strongly correlated with alterations in the inhibition of membrane damaging activity of the protein. Suramin binding to hsPLA2GIIA was also studied by MD simulations, which demonstrated that altered intermolecular potential energy of the suramin/mutant complexes was a reliable indicator of affinity change. Although residues in the C-terminal region play a major role in the stabilization of the hsPLA2GIIA/suramin complex, attractive and repulsive hydrophobic and electrostatic interactions with residues throughout the protein together with the adoption of a bent suramin conformation, all contribute to the stability of the complex. Analysis of the hsPLA2GIIA/suramin interactions allows the prediction of the properties of suramin analogues with improved binding and higher affinities which may be candidates for novel phospholipase A(2) inhibitors.

Mapping of the structural determinants of artificial and biological membrane damaging activities of a Lys49 phospholipase A2 by scanning alanine mutagenesis.

Scanning alanine mutagenesis has been used to study the structural determinants of several activities of bothropstoxin-I (BthTx-I), a lysine 49 Phospholipases A(2) from the venom of Bothrops jararacussu. A total of 31 mutants were generated in the interfacial recognition site and C-terminal loop regions of the protein. The effects of mutagenesis on the in vivo myotoxic activity, the cytolytic activity against cultured C2C12 myoblasts, the bactericidal activity, and the Ca(2+)-independent membrane damaging activity against liposome membranes were compared. Residues 116-119 and 122-125 in the C-terminal loop region are structural determinants for these activities, indicating that membrane permeabilization by the BthTx-I is an important general property in all the measured effects. The structural determinants of myotoxicity and myoblast membrane permeabilization are highly correlated, demonstrating that cultured C2C12 myoblasts are a good model for the myotoxic effect. However, comparison of the structural determinants for all activities revealed several differences in the structural determinants between the effects against myoblast and bacterial membranes, and further differences when compared to the liposome membrane damaging effect. These membrane dependent effects are interpreted to be the consequence of differences in the activation of the membrane bound form of the protein on biological and artificial membranes.

Insights on calcium-independent phospholipid membrane damage by Lys49-PLA2 using tryptophan scanning mutagenesis of bothropstoxin-I from Bothrops jararacussu.

Bothropstoxin-I (BthTx-I) is a homodimeric Lys49-PLA2 from the venom of the snake Bothrops jararacussu, which lacks hydrolytic activity against phospholipid substrates, yet permeabilizes membranes by a Ca2+-independent mechanism. The interaction of the BthTx-I with model membranes has been studied by intrinsic tryptophan fluorescence emission (ITFE) spectroscopy. Nine separate mutants have been created each with a unique tryptophan residue located at a different position in the interfacial recognition site (IRS) of the protein. The rapid and efficient Ca2+-independent membrane damage against unilamellar liposomes composed of DPPC/DMPA in a 9:1 molar ratio was unaffected by these substitutions. Binding studies revealed low protein affinity for these liposomes and no changes were observed in the ITFE properties. In contrast, the binding of all mutants to DPPC/DMPA liposomes in a 1:1 molar ratio was stronger, and was correlated with altered ITFE properties. The blue-shifted emission spectra and increased emission intensity of mutants at positions 31, 67 and 115-117 in the interface recognition surface of the protein suggest these regions are partially inserted into the membrane. These results are consistent with a model for the Ca2+-independent membrane damaging mechanism that involves a transient interaction of the protein with the outer phospholipid leaflet of the target membrane.

Viral studies in burkitt lymphoma: association with Epstein-Barr virus but not HHV-8.

Burkitt lymphoma (BL) is a highly aggressive non-Hodgkin lymphoma, composed of a monomorphic population of medium-sized B cells with a high proliferation rate and a consistent MYC translocation. Epstein-Barr virus (EBV) has been associated with BL with different frequencies depending on the clinical variant. Kaposi sarcoma-associated herpesvirus, or human herpesvirus 8 (HHV-8), infects a wide range of normal cells, having a well-established role in the pathogenesis of various neoplasms, including Kaposi sarcoma, primary effusion lymphoma, multicentric Castleman disease (MCD) and MCD-associated plasmablastic lymphoma. In secondary immunodeficiencies, such as HIV-1 infection and organ transplantation, HHV-8 is considered an opportunistic pathogen linked to the development of lymphomas in patients with AIDS and HIV + patients. We studied the association of EBV and HHV-8 by immunohistochemical analysis, in situ hybridization, and polymerase chain reaction in a large number of well-characterized BLs. EBV was present in 45.0% of all BL cases with higher incidence in the pediatric group; most cases were EBV type A. We found no association of BL with HHV-8 in EBV + BL or in EBV-cases, including the HIV + BL group.

Permeabilization of E. coli K12 inner and outer membranes by bothropstoxin-I, A LYS49 phospholipase A2 from Bothrops jararacussu.

Although lacking catalytic activity, the Lys49-PLA(2)s damage artificial membranes by a Ca(2+)-independent mechanism, and demonstrate a potent bactericidal effect. The relationship between the membrane-damaging activity and bactericidal effect of bothropstoxin-I (BthTx-I), a Lys49-PLA(2) from the venom of Bothrops jararacussu, was evaluated for the wild-type protein and a series of site-directed mutants in the active site and C-terminal regions of the protein. The membrane permeabilization effect against the inner and outer membranes of Escherichia coli K12 was evaluated by fluorescence changes of Sytox Green and N-phenyl-N-naphthylamine, respectively. With the exception of H48Q, all mutants reduced the bactericidal activity, which correlated with a reduction of the permeabilization effect both against the inner bacterial membrane. No significant differences in the permeabilization of the bacterial outer membrane were observed between the native, wild-type recombinant and mutant proteins. These results suggest different permeabilization mechanisms against the inner and outer bacterial membranes. Furthermore, the structural determinants of bacterial inner membrane damage identified in this study correlate with those previously observed for artificial membrane permeabilization, suggesting that a common mechanism of membrane damage underlies the two effects.

Structural determinants of the hyperalgesic activity of myotoxic Lys49-phospholipase A2.

BACKGROUND: Bothropstoxin-I (BthTx-I) is a Lys49-phospholipase A2 (Lys49-PLA2) from the venom of Bothrops jararacussu, which despite of the lack of catalytic activity induces myotoxicity, inflammation and pain. The C-terminal region of the Lys49-PLA2s is important for these effects; however, the amino acid residues that determine hyperalgesia and edema are unknown. The aim of this study was to characterize the structural determinants for the Lys49-PLA2-induced nociception and inflammation. METHODS: Scanning alanine mutagenesis in the active-site and C-terminal regions of BthTx-I has been used to study the structural determinants of toxin activities. The R118A mutant was employed as this substitution decreases PLA2 myotoxicity. In addition, K115A and K116A mutants - which contribute to decrease cytotoxicity - and the K122A mutant - which decreases both myotoxicity and cytotoxicity - were also used. The H48Q mutant - which does not interfere with membrane damage or myotoxic activity - was used to evaluate if the PLA2 catalytic site is relevant for the non-catalytic PLA2-induced pain and inflammation. Wistar male rats received intraplantar injections with mutant PLA2. Subsequently, hyperalgesia and edema were evaluated by the paw pressure test and by a plethysmometer. Native and recombinant BthTx-I were used as controls. RESULTS: Native and recombinant BthTx-I induced hyperalgesia and edema, which peaked at 2 h. The R118A mutant did not induce nociception or edema. The mutations K115A and K116A abolished hyperalgesia without interfering with edema. Finally, the K122A mutant did not induce hyperalgesia and presented a decreased inflammatory response. CONCLUSIONS: The results obtained with the BthTx-I mutants suggest, for the first time, that there are distinct residues responsible for the hyperalgesia and edema induced by BthTx-I. In addition, we also showed that cytolytic activity is essential for the hyperalgesic effect but not for edematogenic activity, corroborating previous data showing that edema and hyperalgesia can occur in a non-dependent manner. Understanding the structure-activity relationship in BthTx-I has opened new possibilities to discover the target for PLA2-induced pain.

Topology of the substrate-binding site of a Lys49-phospholipase A2 influences Ca2+-independent membrane-damaging activity.

BthTx-I (bothropstoxin-I) is a myotoxic Lys49-PLA2 (phospholipase A2 with Lys49) isolated from Bothrops jararacussu venom, which damages liposome membranes by a Ca2+-independent mechanism. The highly conserved Phe5/Ala102/Phe106 motif in the hydrophobic substrate-binding site of the Asp49-PLA2s is substituted by Leu5/Val102/Leu106 in the Lys49-PLA2s. The Leu5/Val102/Leu106 triad in BthTx-I was sequentially mutated via all single- and double-mutant combinations to the Phe5/Ala102/Phe106 mutant. All mutants were expressed as inclusion bodies in Escherichia coli, and the thermal stability (Tm), together with the myotoxic and Ca2+-independent membrane-damaging activities of the recombinant proteins, were evaluated. The far-UV CD profiles of the native, wild-type recombinant and the L106F (Leu106-->Phe) and L5F/F102A/L106F mutant proteins were identical. The L5F, V102A, L5F/V102A and V102A/L106F mutants showed distorted far-UV CD profiles; however, only the L5F and L5F/V102A mutants showed significant decreases in Tm. Alterations in the far-UV CD spectra correlated with decreased myotoxicity and protein-induced release of a liposome-entrapped marker. However, the V102A/L106F and L5F/V102A/L106F mutants, which presented high myotoxic activities, showed significantly reduced membrane-damaging activity. This demonstrates that the topology of the substrate-binding region of BthTx-I has a direct effect on the Ca2+-independent membrane damage, and implies that substrate binding retains an important role in this process.

Mapping structural determinants of biological activities in snake venom phospholipases A2 by sequence analysis and site directed mutagenesis.

In addition to their catalytic activity, snake venom phospholipases A2 (vPLA2) present remarkable diversity in their biological effects. Sequence alignment analyses of functionally related PLA2 are frequently used to predict the structural determinants of these effects, and the predictions are subsequently evaluated by site directed mutagenesis experiments and functional assays. In order to improve the predictive potential of computer-based analysis, a simple method for scanning amino acid variation analysis (SAVANA) has been developed and included in the analysis of the lysine 49 PLA2 myotoxins (Lys49-PLA2). The SAVANA analysis identified positions in the C-terminal loop region of the protein, which were not identified using previously available sequence analysis tools. Site directed mutagenesis experiments of bothropstoxin-I, a Lys49-PLA2 isolated from the venom of Bothrops jararacussu, reveals that these residues are exactly those involved in the determination of myotoxic and membrane damaging activities. The SAVANA method has been used to analyse presynaptic neurotoxic and anti-coagulant vPLA2s, and the predicted structural determinants of these activities are in excellent agreement with the available results of site directed mutagenesis experiments. The positions of residues involved in the myotoxic and neurotoxic determinants demonstrate significant overlap, suggesting that the multiple biological effects observed in many snake vPLA2s are a consequence of superposed structural determinants on the protein surface.

Active site mutants of human secreted Group IIA Phospholipase A2 lacking hydrolytic activity retain their bactericidal effect.

The Human Secreted Group IIA Phospholipase A(2) (hsPLA2GIIA) presents potent bactericidal activity, and is considered to contribute to the acute-phase immune response. Hydrolysis of inner membrane phospholipids is suggested to underlie the bactericidal activity, and we have evaluated this proposal by comparing catalytic activity with bactericidal and liposome membrane damaging effects of the G30S, H48Q and D49K hsPLA2GIIA mutants. All mutants showed severely impaired hydrolytic activities against mixed DOPC:DOPG liposome membranes, however the bactericidal effect against Micrococcus luteus was less affected, with 50% killing at concentrations of 1, 3, 7 and 9 µg/mL for the wild-type, D49K, H48Q and G30S mutants respectively. Furthermore, all proteins showed Ca(2+)-independent damaging activity against liposome membranes demonstrating that in addition to the hydrolysis-dependent membrane damage, the hsPLA2GIIA presents a mechanism for permeabilization of phospholipid bilayers that is independent of catalytic activity, which may play a role in the bactericidal function of the protein.

Structural determinants of the hyperalgesic activity of myotoxic Lys49-phospholipase A2

Abstract Background Bothropstoxin-I (BthTx-I) is a Lys49-phospholipase A2 (Lys49-PLA2) from the venom of Bothrops jararacussu, which despite of the lack of catalytic activity induces myotoxicity, inflammation and pain. The C-terminal region of the Lys49-PLA2s is important for these effects; however, the amino acid residues that determine hyperalgesia and edema are unknown. The aim of this study was to characterize the structural determinants for the Lys49-PLA2-induced nociception and inflammation. Methods Scanning alanine mutagenesis in the active-site and C-terminal regions of BthTx-I has been used to study the structural determinants of toxin activities. The R118A mutant was employed as this substitution decreases PLA2 myotoxicity. In addition, K115A and K116A mutants which contribute to decrease cytotoxicity and the K122A mutant which decreases both myotoxicity and cytotoxicity were also used. The H48Q mutant which does not interfere with membrane damage or myotoxic activity was used to evaluate if the PLA2 catalytic site is relevant for the non-catalytic PLA2-induced pain and inflammation. Wistar male rats received intraplantar injections with mutant PLA2. Subsequently, hyperalgesia and edema were evaluated by the paw pressure test and by a plethysmometer. Native and recombinant BthTx-I were used as controls. Results Native and recombinant BthTx-I induced hyperalgesia and edema, which peaked at 2 h. The R118A mutant did not induce nociception or edema. The mutations K115A and K116A abolished hyperalgesia without interfering with edema. Finally, the K122A mutant did not induce hyperalgesia and presented a decreased inflammatory response. Conclusions The results obtained with the BthTx-I mutants suggest, for the first time, that there are distinct residues responsible for the hyperalgesia and edema induced by BthTx-I. In addition, we also showed that cytolytic activity is essential for the hyperalgesic effect but not for edematogenic activity, corroborating previous data showing that edema and hyperalgesia can occur in a non-dependent manner. Understanding the structure-activity relationship in BthTx-I has opened new possibilities to discover the target for PLA2-induced pain.

Structural determinants of the hyperalgesic activity of myotoxic Lys49-phospholipase A2

Background Bothropstoxin-I (BthTx-I) is a Lys49-phospholipase A2 (Lys49-PLA2) from the venom of Bothrops jararacussu, which despite of the lack of catalytic activity induces myotoxicity, inflammation and pain. The C-terminal region of the Lys49-PLA2s is important for these effects; however, the amino acid residues that determine hyperalgesia and edema are unknown. The aim of this study was to characterize the structural determinants for the Lys49-PLA2-induced nociception and inflammation. Methods Scanning alanine mutagenesis in the active-site and C-terminal regions of BthTx-I has been used to study the structural determinants of toxin activities. The R118A mutant was employed as this substitution decreases PLA2 myotoxicity. In addition, K115A and K116A mutants - which contribute to decrease cytotoxicity - and the K122A mutant - which decreases both myotoxicity and cytotoxicity - were also used. The H48Q mutant - which does not interfere with membrane damage or myotoxic activity - was used to evaluate if the PLA2 catalytic site is relevant for the non-catalytic PLA2-induced pain and inflammation. Wistar male rats received intraplantar injections with mutant PLA2. Subsequently, hyperalgesia and edema were evaluated by the paw pressure test and by a plethysmometer. Native and recombinant BthTx-I were used as controls. Results Native and recombinant BthTx-I induced hyperalgesia and edema, which peaked at 2 h. The R118A mutant did not induce nociception or edema. The mutations K115A and K116A abolished hyperalgesia without interfering with edema. Finally, the K122A mutant did not induce hyperalgesia and presented a decreased inflammatory response. Conclusions The results obtained with the BthTx-I mutants suggest, for the first time, that there are distinct residues responsible for the hyperalgesia and edema induced by BthTx-I. In addition, we also showed that cytolytic activity is essential for the hyperalgesic effect but not for edematogenic activity, corroborating previous data showing that edema and hyperalgesia can occur in a non-dependent manner. Understanding the structure-activity relationship in BthTx-I has opened new possibilities to discover the target for PLA2-induced pain.(AU)

Hodgkin's lymphoma presenting as dominant gastric lesion in immunocompetent patients: report of 5 cases with EBV analysis.

Primary Hodgkin's lymphoma (HL) of the stomach is an extremely rare entity. Most cases of gastric involvement by HL are observed in the setting of disseminated disease. The nonspecific nature of the symptoms and endoscopic findings, which include a large malignant-looking ulcer and mass or wall thickening, together with the considerable histological overlap between HLs and some non-HLs or undifferentiated carcinoma, make the surgical resection diagnosis extremely difficult. An accurate diagnosis is important as treatment and outcome differ significantly for these neoplasms. In small endoscopic gastric biopsies and even in postoperative specimens, the precise histological diagnosis of HL is particularly challenging. Here, the authors report 5 cases of 2 women and 3 men aged 22 to 68, with gastric involvement by classic HLs-3 primary gastric HLs and 2 as part of widespread disease. All 5 patients presented with digestive symptoms. At endoscopy, the lesions presented as ulcerated and elevated lesions, with or without mucosal thickening. Four patients were misdiagnosed in the preoperative biopsy or in the gastrectomy specimen. Association with Epstein-Barr virus (EBV) was detected in 4 cases, with a predominance of subtype A EBV. These cases illustrate the significant difficulties, both clinical and pathological, in achieving the diagnosis of HL involving the stomach in immunocompetent patients.

Clinicopathologic and molecular features of 122 Brazilian cases of nodal and extranodal NK/T-cell lymphoma, nasal type, with EBV subtyping analysis.

Extranodal natural killer/T-cell lymphoma, nasal type (NK/TCL) is more prevalent in Asia and in some areas of South and Central America, but it is rarely seen in the United States and Europe. In this study, a series of 122 cases of NK/TCL from Brazil was analyzed with respect to clinicopathologic features. Clinical characteristics and geographic distribution were evaluated in 97 cases of nasal/nasopharyngeal region and 23 cases in extranasal sites including 6 nodal cases. Clinical staging and follow-up information was available in a subset of 21 patients. All cases harbored Epstein-Barr virus (EBV), 95% and 85% expressed cytoplasmic CD3 and CD56, respectively, and all cases were positive for at least 1 marker for cytotoxic granules. The global distribution of EBV subtypes showed predominance of strain subtype A, 89%, and subtype B, 11%. No dual infections were detected. TCR-γ TCR-gene rearrangement was observed in 7 cases; all of them extranodal. Three of TCR-γ(+) cases showed EBV subtype A. Two TCR-γ(+)/CD56(+) cases showed EBV subtype B. Geographic distribution of NK/TCL showed higher frequency in the southeast and northeast regions of Brazil. Striking differences among geographic regions were seen with the vast majority of EBV subtype B (86%) occurring in the south and southeast regions.

Postsplenectomy sclerosing extramedullary hematopoietic tumor with unexpected good clinical evolution: morphologic, immunohistochemical, and molecular analysis of one case and review of the literature.

Sclerosing extramedullary hematopoietic tumor has been described as a rare manifestation of chronic myeloproliferative neoplasm. The lack of knowledge about this entity has caused it to be mistaken for many types of nonhematopoietic and hematopoietic tumors. We present the case of a 71-year-old lady with a long history of primary myelofibrosis, which developed multiple abdominal sclerosing extramedullary hematopoietic tumors with good clinical evolution. Nonchronic myeloid leukemia myeloproliferative neoplasm included a JAK2 mutation as part of the diagnosis algorithm. Particularly, idiopathic myelofibrosis is related with a JAK2 mutation in 50% of the cases with a pejorative prognosis. The absence of JAK2 demonstrated in the paraffin samples of the tumors may be related to the unusual evolution in this particular case. Morphologically differential diagnoses considered in the evaluation of this entity and in our case included sarcomas mainly liposarcoma, anaplastic carcinoma, and Hodgkin lymphoma.

Composite lymphoma: EBV-positive classic Hodgkin lymphoma and peripheral T-cell lymphoma: a case report.

Composite lymphomas are rare and defined as hematopoietic neoplasms with more than 1 malignant lymphomatous clone showing different phenotypic features. Of all possible combinations between non-Hodgkin lymphomas, B cell or T cell, and Hodgkin lymphoma, the least frequent are the ones combining T-cell non-Hodgkin lymphoma and classic Hodgkin lymphoma. We report a case of a 55-year-old woman with cervical and mediastinal lymphadenopathy, fever, weight loss, and night sweats. A cervical lymph node biopsy revealed a composite lymphoma with classic Hodgkin lymphoma and peripheral T-cell lymphoma components. The bone marrow was not involved. The patient refused treatment and died of disease progression 2 months after diagnosis. The biopsied lymph node showed 2 distinct populations, one composed of large cells including typical Reed-Sternberg cells and their variants, with expression of CD30, CD15, PAX5, and LMP-1. The other component was more abundant and comprised polymorphic medium-sized cells with convoluted nuclei; CD3, CD5, CD2, and CD4 expression; and negativity for CD30, cytotoxic granules, and B-cell markers. Epstein-Barr virus DNA of subtype A was identified only in the Hodgkin cells. Clonal T-cell receptor gamma and beta gene rearrangements were detected in the T-cell component, whereas monoclonal immunoglobulin H gene rearrangement was found in the Hodgkin cells.

Primary and secondary T-cell lymphomas of the breast: clinico-pathologic features of 11 cases.

Breast involvement by non-Hodgkin lymphomas is rare, and exceptional for T-cell lymphomas; we studied the morphologic, immunophenotypic, and clinical features of 11 patients with T-cell non-Hodgkin lymphomas involving the breast. Four cases fulfilled the definition criteria for primary breast lymphomas, 3 females and 1 male, with a median age of 51 years. One primary breast lymphomas was T-cell lymphoma unspecified, other was subcutaneous panniculitis-like T-cell lymphoma, and 2 cases were anaplastic large cell lymphomas. One of the anaplastic large cell lymphoma cases was found surrounding a silicone breast implant and presented as clinically as mastitis; whereas the other case occurred in a man. T-cell lymphoma secondarily involved the breast in 7 patients, all women and 1 bilateral, with a median age of 29 years. These secondary breast lymphomas occurred as part of widespread nodal or leukemic disease. Three patients had adult T-cell leukemia/lymphoma, including the patient with bilateral lesions, 3 others had precursor T-lymphoblastic lymphoma/leukemia, and the other presented with a peripheral-T-cell lymphoma non otherwise specified type. Breast T-cell lymphomas are very infrequent and are morphologically and clinically heterogeneous.

Desmoplastic small round cell tumor of the kidney mimicking Wilms tumor: a case report and review of the literature.

Desmoplastic small round cell tumor (DSRCT) is a rare, aggressive, malignant neoplasm usually present with the widespread abdominal serosal involvement and affects mainly adolescents and young adults. When presenting within visceral organs, as kidney, the diagnosis of DSRCT imposes significant difficulties. We present a case of primary DSRCT of the kidney in a 10-year-old boy mimicking clinically and pathologically Wilms tumor. The tumor showed morphologic and immunohistochemical features of DSRCT and the presence of the Ewing sarcoma and Wilm tumor 1 fusion transcripts resulting from the t(11;22) (p13;q12) reciprocal translocation. DSRCT should be considered in the differential diagnosis of Wilm tumor and other small blue-round cell tumors of the kidney.

Analysis of human T-cell lymphotropic virus in CD25+ anaplastic large cell lymphoma in children.

Anaplastic large cell lymphoma (ALCL) is recognized as 2 distinct diseases: anaplastic lymphoma kinase (ALK)+ ALCL and ALK- ALCL. ALK+ ALCL occurs in younger patients and has a better prognosis. Human T-cell lymphotropic virus (HTLV-1) is linked to the development of adult T-cell leukemia/lymphoma (ATLL), which frequently expresses CD25. CD25 is significantly expressed in childhood ALCL. In Brazil, HTLV-1 infection is endemic, and vertical transmission is responsible for spread to children. Of HTLV-1 carriers, 90% or more remain asymptomatic. Some cases of adult HTLV-1-related lymphomas have characteristics of ALCL but are considered CD30+ ATLL subtypes. No similar cases have been described in children. We analyzed 33 cases of pediatric ALCL, CD25+ and CD25-, for proviral HTLV-1 DNA. All cases corresponded to the common histologic ALCL type and were CD30+ in virtually all neoplastic cells. ALK expression was observed in 31 (94%) of 33 cases; CD25 was positive in 27 (82%), including 1 ALK- ALCL case. There was a strong positive correlation between ALK and CD25 expression. None of the cases showed proviral HTLV-1 DNA. ALCL in children has no relationship with HTLV-1; the frequent CD25 expression must be explained by a mechanism different from that in ATLL.

Active-site mutagenesis of a Lys49-phospholipase A2: biological and membrane-disrupting activities in the absence of catalysis.

Bothropstoxin-I (BthTx-I) is a myotoxic phospholipase A(2) variant present in the venom of Bothrops jararacussu, in which the Asp(49) residue is replaced with a lysine, which damages artificial membranes by a Ca(2+)-independent mechanism. Wild-type BthTx-I and the mutants Lys(49)-->Asp, His(48)-->Gln and Lys(122)-->Ala were expressed in Escherichia coli BL21(DE3) cells, and the hydrolytic, myotoxic and membrane-damaging activities of the recombinant proteins were compared with native BthTx-I purified from whole venom. The Ca(2+)-independent membrane-damaging and myotoxic activities of the native and wild-type recombinant BthTx-I, His(48)Gln and Lys(49)Asp mutants were similar; however, the Lys(122)Ala mutant demonstrated reduced levels of both activities. Although a low hydrolytic activity against a mixed phospholipid substrate was observed with native BthTx-I, no substrate hydrolysis was detected with the wild-type recombinant enzyme or any of the mutants. In the case of the Lys(49)Asp mutant, this demonstrates that the absence of catalytic activity in Lys(49)-PLA(2) is not a consequence of the single Asp(49)-->Lys replacement. Furthermore, these results provide unambiguous evidence that the Ca(2+)-independent membrane-damaging and myotoxic activities are maintained in the absence of hydrolysis. The evidence favours a model for a hydrolysis-independent, membrane-damaging mechanism involving an interaction of the C-terminal region of BthTx-I with the target membrane.

Distinct sites for myotoxic and membrane-damaging activities in the C-terminal region of a Lys49-phospholipase A2.

Bothropstoxin-I (BthTx-I) is a Lys(49)-phospholipase A(2) from the venom of Bothrops jararacussu which demonstrates both myotoxic and Ca(2+)-independent membrane-damaging activities. The structural determinants of these activities are poorly defined, therefore site-directed mutagenesis has been used to substitute all cationic and aromatic residues between positions 115 and 129 in the C-terminal loop region of the protein. Substitution of lysine and arginine residues with alanine in the region 117-122 resulted in a significant reduction of myotoxic activity of the recombinant BthTx-I. With the exception of Lys(122), these same substitutions did not significantly alter the Ca(2+)-independent membrane-damaging activity. In contrast, substitution of the positively-charged residues at positions 115, 116 and 122 resulted in reduced Ca(2+)-independent membrane-damaging activity but, with the exception of Lys(122), had no effect on myotoxicity. These results indicate that the two activities are independent and are determined by discrete yet partially overlapping motifs in the C-terminal loop. Results from site-directed mutagenesis of the aromatic residues in the same part of the protein suggest that a region including residues 115-119 interacts superficially with the membrane interface and that the residues around position 125 partially insert into the lipid membrane. These results represent the first detailed mapping of a myotoxic site in a phospholipase A(2), and support a model of a Ca(2+)-independent membrane-damaging mechanism in which the C-terminal region of BthTx-I interacts with and contributes to the perturbation of the phospholipid bilayer.