Mycobacterium leprae binds to a major human peripheral nerve glycoprotein myelin P zero (P0)

We have previously shown that a major phosphorylated 25-kDa glycoprotein of the human peripheral nerve binds to Mycobacterium leprae. In the present study, we confirm that the 25-kDa glycoprotein of the human peripheral nerve is myelin P zero (P₀) by immunoprecipitation and Western blot experiments using monoclonal antibodies to myelin P₀. Immunohistochemical studies on human nerve using these antibodies to myelin P₀ exhibited a strong immunoreactivity to the myelin and Schwann cells. Myelin P₀ is a peripheral nerve specific protein; therefore it could likely be one of the key target molecules for M. leprae binding/internalization or even contact-dependent demyelination. This finding of M. leprae binding to myelin P₀ adds to the present understanding on neural predilection of M. leprae.     

Four novel bis-(naphtho-gamma-pyrones) isolated from Fusarium species as inhibitors of HIV-1 integrase

Integration of viral DNA into host cell DNA is an essential step in retroviral (HIV-1) replication and is catalyzed by HIV-1 integrase. HIV-1 integrase is a novel therapeutic target and is the focus of efforts to identify effective inhibitors that will prevent/or cure HIV infections. Four novel naphtho-gamma-pyrones, belonging to the chaetochromin and ustilaginoidin family, were discovered as inhibitors of HIV-1 integrase from the screening of fungal extracts using a recombinant in vitro assay. These compounds inhibit both the coupled and strand transfer activity of HIV-1 integrase with IC(50) values of 1-3 and 4-12 microM, respectively. The discovery, structure elucidation, chemical modification and the structure-activity relationship of these compounds are described.     

Integracides: tetracyclic triterpenoid inhibitors of HIV-1 integrase produced by Fusarium sp

HIV-1 integrase is a critical enzyme in the replication of HIV-1. It is absent in the host cells and therefore is a good target for treatment of HIV-1 infections. Integracides are members of the tetracyclic triterpenoids family that were isolated from the fermentation broth of a Fusarium sp. Integracide A, a sulfated ester, exhibited significant inhibitory activity against strand transfer reaction of HIV-1 integrase. The discovery, structure elucidation including single crystal X-ray structure and HIV-1 inhibitory activity of these compounds are described.     

QSAR studies in substituted 1,2,3,4,6,7,12,12a-octa-hydropyrazino[2',1':6,1]pyrido[3,4-b]indoles--a potent class of neuroleptics

A series of nineteen substituted 1,2,3,4,6,7,12,12a-octahydropyrazino[2',1':6,1]pyrido[3, 4-b]indoles analogues of neuroleptic drug, Centbutindole have been studied using quantitative structure-activity relationship analysis. The derived models display good fits to the experimental data (r>or=0.75) having good predictive power (r(cv)>or=0.688). The best model describes a high correlation between predicted and experimental activity data (r=0.967). Statistical analysis of the equation populations indicates that hydrophobicity (as measured by pi(R), logP(o/w) and SlogP_VSA8), dipole y and structural parameters in terms of indicator variable, (In(1)) and globularity are important variables in describing the variation in the neuroleptic activity in the series.     

Synthetic and novel biocatalytic resolution studies on (+/-)-5/6/7-acetoxy-4-aryl-3,4-dihydrocoumarins

Eleven (+/-)-5/6/7-acetoxy-4-aryl-3,4-dihydrocoumarins have been synthesised in two steps starting from the coupling of cinnamic acid/substituted cinnamic acid with appropriate phenols, followed by acetylation in 50-83% overall yields. All hydroxy- and acetoxycoumarins were unambiguously identified on the basis of their spectral data. Candida antarctica lipase-catalysed deacetylation of these racemic acetoxydihydrocoumarins in dioxane occurred with moderate enantioselectivity. This is one of the rare examples of resolution using phenolic ester moiety as a remote handle for chiral recognition by a lipase.     

Setaria cervi: in vitro released collagenases and their inhibition by Wuchereria bancrofti infected sera

In vitro released products of adult Setaria cervi females, microfilariae and extracts showed considerable amounts of collagenase activity. On the basis of per mg protein released in vitro, the products of both microfilariae and adult females exhibited comparable activity but this was much higher than that of extract of microfilariae and adult females. Two collagenase enzymes with molecular masses of 50 kDa and 70 kDa were separated using DEAE-sepharose CL6B and Sephadex G-100 column chromatography. The 50 kDa and 70 kDa collagenase exhibited pH optima of 5.2 and 7.0, respectively. Considering specific activity, the 50 kDa enzyme was found to contribute about ten times more collagenase activity as compared to the 70 kDa enzyme. An inhibition study revealed obvious differences between them. Thiol group inhibitors such as N-ethylmaleimide and leupeptin inhibited the 50 kDa enzyme but this was strongly activated by dithiothreitol, a thiol group stabilizer. Alternatively, the 70 kDa enzyme showed a sensitivity to a metal chelator and a serine group inhibitor indicating its metalloserine protease nature. The antifilarial drug diethylcarbamazine did not demonstrate any inhibition under in vitro conditions. Both enzymes were significantly inhibited by antibody IgG separated from Wuchereria bancrofti infected human sera, showing a possible immunoprotective role.     

Contrasting use of CCR5 structural determinants by R5 and R5X4 variants within a human immunodeficiency virus type 1 primary isolate quasispecies

Macrophagetropic R5 human immunodeficiency virus type 1 (HIV-1) isolates often evolve into dualtropic R5X4 variants during disease progression. The structural basis for CCR5 coreceptor function has been studied in a limited number of prototype strains and suggests that R5 and R5X4 Envs interact differently with CCR5. However, differences between unrelated viruses may reflect strain-specific factors and do not necessarily represent changes resulting from R5 to R5X4 evolution of a virus in vivo. Here we addressed CCR5 domains involved in fusion for a large set of closely related yet functionally distinct variants within a primary isolate swarm, employing R5 and R5X4 Envs derived from the HIV-1 89.6(PI) quasispecies. R5 variants of 89.6(PI) could fuse using either N-terminal or extracellular loop CCR5 sequences in the context of CCR5/CXCR2 chimeras, similar to the unrelated R5 strain JRFL, but R5X4 variants of 89.6(PI) were highly dependent on the CCR5 N terminus. Similarly, R5 89.6(PI) variants and isolate JRFL tolerated N-terminal CCR5 deletions, but fusion by most R5X4 variants was markedly impaired. R5 89.6(PI) Envs also tolerated multiple extracellular domain substitutions, while R5X4 variants did not. In contrast to CCR5 use, fusion by R5X4 variants of 89.6(PI) was largely independent of the CXCR4 N-terminal region. Thus, R5 and R5X4 species from a single swarm differ in how they interact with CCR5. These results suggest that R5 Envs possess a highly plastic capacity to interact with multiple CCR5 regions and support the concept that viral evolution in vivo results from the emergence of R5X4 variants with the capacity to use the CXCR4 extracellular loops but demonstrate less-flexible interactions with CCR5 that are strongly dependent on the N-terminal region.     

Observed hysteresis of virus capsid disassembly is implicit in kinetic models of assembly

For many protein multimers, association and dissociation reactions fail to reach the same end point; there is hysteresis preventing one and/or the other reaction from equilibrating. We have studied in vitro assembly of dimeric hepatitis B virus (HBV) capsid protein and dissociation of the resulting T = 4 icosahedral capsids. Empty HBV capsids composed of 120 capsid protein dimers were more resistant to dissociation by dilution or denaturants than anticipated from assembly experiments. Using intrinsic fluorescence, circular dichroism, and size exclusion chromatography, we showed that denaturants dissociate the HBV capsids without unfolding the capsid protein; unfolding of dimer only occurred at higher denaturant concentrations. The apparent energy of interaction between dimers measured in dissociation experiments was much stronger than when measured in assembly studies. Unlike assembly, capsid dissociation did not have the concentration dependence expected for a 120-subunit complex; consequently the apparent association energy systematically varied with reactant concentration. These data are evidence of hysteresis for HBV capsid dissociation. Simulations of capsid assembly and dissociation reactions recapitulate and provide an explanation for the observed behavior; these results are also applicable to oligomeric and multidomain proteins. In our calculations, we find that dissociation is impeded by temporally elevated concentrations of intermediates; this has the paradoxical effect of favoring re-assembly of those intermediates despite the global trend toward dissociation. Hysteresis masks all but the most dramatic decreases in contact energy. In contrast, assembly reactions rapidly approach equilibrium. These results provide the first rigorous explanation of how virus capsids can remain intact under extreme conditions but are still capable of "breathing." A biological implication of enhanced stability is that a triggering event may be required to initiate virus uncoating.     

Heat shock protein 27 controls apoptosis by regulating Akt activation

Activation of the serine-threonine kinase Akt by cytokines, chemokines, and bacterial products delays constitutive neutrophil apoptosis, resulting in a prolonged inflammatory response. We showed previously that Akt exists in a signaling complex with p38 MAPK, MAPK-activated protein kinase-2 (MAPKAPK-2), and heat shock protein-27 (Hsp27); and Hsp27 dissociates from the complex upon neutrophil activation. To better understand the regulation of this signaling module, the hypothesis that Akt phosphorylation of Hsp27 regulates its interaction with Akt was tested. The present study shows that Akt phosphorylated Hsp27 on Ser-82 in vitro and in intact cells, and phosphorylation of Hsp27 resulted in its dissociation from Akt. Additionally, the interaction between Hsp27 and Akt was necessary for activation of Akt in intact neutrophils. Constitutive neutrophil apoptosis was accelerated by sequestration of Hsp27 from Akt, and this enhanced rate of apoptosis was reversed by introduction of constitutively active recombinant Akt. Our results define a new mechanism by which Hsp27 regulates apoptosis, through control of Akt activity.     

Hemozoin formation in malaria: a two-step process involving histidine-rich proteins and lipids

Major blood stage antimalarial drugs like chloroquine and artemisinin target the heme detoxification process of the malaria parasite. Hemozoin formation reactions in vitro using the Plasmodium falciparum histidine-rich protein-2 (Pfhrp-2), lipids, and auto-catalysis are slow and could not explain the speed of detoxification needed for parasite survival. Here, we show that malarial hemozoin formation is a coordinated two component process involving both lipids and histidine-rich proteins. Hemozoin formation efficiency in vitro is 1-2% with Pfhrp-2 and 0.25-0.5% with lipids. We added lipids after 9h in a 12h Pfhrp-2 mediated reaction that resulted in sixfold increase in hemozoin formation. However, a lipid mediated reaction in which Pfhrp-2 was added after 9h produced only twofold increase in hemozoin production compared to the reaction with Pfhrp-2 alone. Synthetic peptides corresponding to the Pfhrp-2 heme binding sequences, based on repeats of AHHAAD, neither alone nor in combination with lipids were able to generate hemozoin in vitro. These results indicate that hemozoin formation in malaria parasite involves both the lipids and the scaffolding proteins. Histidine-rich proteins might facilitate hemozoin formation by binding with a large number of heme molecules, and facilitating the dimer formation involving iron-carboxylate bond between two heme molecules, and lipids may then subsequently assist the mechanism of long chain formation, held together by hydrogen bonds or through extensive networking of hydrogen bonds.