Therefore, we conclude that this respective E2 peptides may displace gp120 and disturb the interface between gp120 and gp41 after CD4 or coreceptor binding

Therefore, we conclude that this respective E2 peptides may displace gp120 and disturb the interface between gp120 and gp41 after CD4 or coreceptor binding. epitope, and flanking amino acids may contribute to binding efficiency.(DOC) pone.0054452.s003.doc (42K) GUID:?D1669B3D-1ACE-46C1-A4F3-6FC7663EBB44 Abstract A strategy for antiviral drug discovery is the elucidation and imitation of viral interference mechanisms. HIV-1 patients benefit from a coinfection with GB Computer virus C (GBV-C), since HIV-positive individuals with long-term GBV-C viraemia show better survival rates than HIV-1 patients without persisting GBV-C. A direct influence of GBV-C on HIV-1 replication has been shown in coinfection experiments. GBV-C is usually a human non-pathogenic member of the family that can replicate in T and B cells. Therefore, GBV-C shares partly the same ecological niche with HIV-1. In earlier work we have exhibited that recombinant glycoprotein E2 of GBV-C and peptides derived from the E2 N-terminus interfere with HIV entry. In this study we investigated the underlying mechanism. PTC-209 HBr Performing a virus-cell PTC-209 HBr PTC-209 HBr fusion assay and temperature-arrested HIV-infection kinetics, we provide evidence that this HIV-inhibitory E2 peptides interfere with late HIV-1 access steps after the engagement of gp120 with CD4 receptor and coreceptor. Binding and competition experiments revealed that this N-terminal E2 peptides bind to the disulfide loop region of HIV-1 transmembrane protein gp41. In conjunction with computational analyses, we recognized sequence similarities between the N-termini of GBV-C E2 and the HIV-1 glycoprotein gp120. This similarity appears to enable the GBV-C E2 N-terminus to interact with the HIV-1 gp41 disulfide loop, a crucial domain name involved in the gp120-gp41 interface. Furthermore, the results of the present study provide initial proof of concept that peptides targeted to the gp41 disulfide loop are able to inhibit HIV fusion and should inspire the development of this new class of HIV-1 access PTC-209 HBr inhibitors. Introduction GB computer virus C (GBV-C) is usually a common human virus that can be transmitted sexually, parenterally and vertically from mother to child [1], [2]. Infection of immunocompetent individuals usually leads to clearance of GBV-C viraemia within the first years; however, GBV-C can cause persistent infection in approximately 25% of cases [3]. As a member of the family, for which a fourth genus, termed E2 proteins (Figure S1). In particular, several cysteines (C46, C48, C60) and tryptophans (W55, W65) are highly conserved among GBV-C and HsRad51 GBV-A isolates, suggesting that the respective E2 proteins might also exhibit a similar anti-lentiviral activity. The alignment shown in Figure S1 also reveals that the sequence conservation is less pronounced for the more distantly related E2 proteins of GBV-B and GBV-D. The N-termini of the E2 proteins from GBV-C and HCV show no detectable sequence homology at all rendering functional similarity rather unlikely. The results of several experiments aimed at dissecting the E2-binding domain within gp41 suggest that E2 interacts with the gp41 disulfide loop region. The gp41 disulfide loop region structurally connects the NHR and CHR domains and contains two conserved cysteines [64]. Noteworthy, the N-terminal E2 region contains three cysteine residues (Cys46, Cys48 and Cys60) as well. Previously we could show that variants of the E2 peptides (P4-7s and P6-2s), in which cysteines were replaced with serine residues, lost their HIV-inhibitory capacity [33]. In agreement with these observations, in this study, P4-7s and P6-2s lost their ability to compete with E2 for gp41binding. In addition, the cysteine residues within the disulfide loop peptide appeared to be crucial for PTC-209 HBr the interaction with recombinant E2 protein. This implies that the cysteine residues within the HIV-inhibitory E2 peptides may interfere with the oxidation state of the respective cysteines in the gp41 disulfide loop region. A variety of evidence suggests that a number of viral envelope glycoproteins depend on a dynamic thiol/disulfide balance to mediate virus-cell fusion (reviewed in [65]). For HIV-1 it has been shown that after CD4 binding a cell surface-associated reductase activity leads to cleavage of disulfide bonds at least within gp120 and that this event is obligatory for triggering membrane fusion [66]. However, the insights into the mechanistic role of the disulfide loop cysteines for the fusion reaction are still limited and need further evaluation. Future studies will show, whether reducing agents would change the interference effects of GBV-C E2-derived peptides. Based on cryo-EM structural information, the gp41 transmembrane protein is expected to be at least partially buried in the trimeric gp41-gp120 structure [67]. Thus, the transient states of gp41 appears to be valid HIV-1 inhibitor targets, as evidenced by a number of known HIV-1 fusion inhibitors, including gp41-targeted peptides and low-molecular-weight inhibitors. These inhibitors typically bind to the NHR or CHR regions during the prehairpin stage in order to prevent the formation of the 6-HB. However, Mnch et al. [42] isolated the natural HIV-1 entry inhibitor VIRIP.