Biophysical Investigations of GBV-C E1 Peptides as Potential Inhibitors of HIV-1 Fusion Peptide

Human Pegivirus Type 1: A Common Human Virus That Is Beneficial in Immune-Mediated Disease?

Two groups identified a novel human flavivirus in the mid-1990s. One group named the virus hepatitis G virus (HGV) and the other named it GB Virus type C (GBV-C). Sequence analyses found these two isolates to be the same virus, and subsequent studies found that the virus does not cause hepatitis despite sharing genome organization with hepatitis C virus. Although HGV/GBV-C infection is common and may cause persistent infection in humans, the virus does not appear to directly cause any other known disease state. Thus, the virus was renamed “human pegivirus 1” (HPgV-1) for “persistent G” virus. HPgV-1 is found primarily in lymphocytes and not hepatocytes, and several studies found HPgV-1 infection associated with prolonged survival in people living with HIV. Co-infection of human lymphocytes with HPgV-1 and HIV inhibits HIV replication. Although three viral proteins directly inhibit HIV replication in vitro, the major effects of HPgV-1 leading to reduced HIV-related mortality appear to result from a global reduction in immune activation. HPgV-1 specifically interferes with T cell receptor signaling (TCR) by reducing proximal activation of the lymphocyte specific Src kinase LCK. Although TCR signaling is reduced, T cell activation is not abolished and with sufficient stimulus, T cell functions are enabled. Consequently, HPgV-1 is not associated with immune suppression. The HPgV-1 immunomodulatory effects are associated with beneficial outcomes in other diseases including Ebola virus infection and possibly graft-versus-host-disease following stem cell transplantation. Better understanding of HPgV-1 immune escape and mechanisms of inflammation may identify novel therapies for immune-based diseases.

Surface behavior of peptides from E1 GBV-C protein: Interaction with anionic model membranes and importance in HIV-1 FP inhibition

The interaction between a peptide sequence from GB virus C E1 protein (E1P8) and its structural analogs (E1P8-12), (E1P8-13), and (E1P8-21) with anionic lipid membranes (POPG vesicles and POPG, DPPG or DPPC/DPPG (2:1) monolayers) and their association with HIV-1 fusion peptide (HIV-1 FP) inhibition at the membrane level were studied using biophysical methods. All peptides showed surface activity but leakage experiments in vesicles as well as insertion kinetics in monolayers and lipid/peptide miscibility indicated a low level of interaction: neither E1P8 nor its analogs induced the release of vesicular content and the exclusion pressure values (πe) were clearly lower than the biological membrane pressure (24-30 mN m(-1)) and the HIV-1 FP (35 mN m(-1)). Miscibility was elucidated in terms of the additivity rule and excess free energy of mixing (GE). E1P8, E1P8-12 and E1P8-21 (but not E1P8-13) induced expansion of the POPG monolayer. The mixing process is not thermodynamically favored as the positive GE values indicate. To determine how E1 peptides interfere in the action of HIV-1 FP at the membrane level, mixed monolayers of HIV-1 FP/E1 peptides (2:1) and POPG were obtained. E1P8 and its derivative E1P8-21 showed the greatest HIV-1 FP inhibition. The LC-LE phase lipid behavior was morphologically examined via fluorescence microscopy (FM) and atomic force microscopy (AFM). Images revealed that the E1 peptides modify HIV-1 FP-lipid interaction. This fact may be attributed to a peptide/peptide interaction as indicated by AFM results. Finally, hemolysis assay demonstrated that E1 peptides inhibit HIV-1 FP activity.