Abstract
BackgroundInteractions between the HIV-1 envelope glycoprotein (Env) and its primary receptor CD4 are influenced by the physiological setting in which these events take place. In this study, we explored the surface chemistry of HIV-1 Env constructs at a range of pH and salinities relevant to mucosal and systemic compartments through electrophoretic mobility (EM) measurements. Sexual transmission events provide a more acidic environment for HIV-1 compared to dissemination and spread of infection occurring in blood or lymph node. We hypothesize functional, trimeric Env behaves differently than monomeric forms.ResultsThe dynamic electrophoretic fingerprint of trimeric gp140 revealed a change in EM from strongly negative to strongly positive as pH increased from that of the lower female genital tract (pHx) to that of the blood (pHy). Similar findings were observed using a trimeric influenza Haemagglutinin (HA) glycoprotein, indicating that this may be a general attribute of trimeric viral envelope glycoproteins. These findings were supported by computationally modeling the surface charge of various gp120 and HA crystal structures. To identify the behavior of the infectious agent and its target cells, EM measurements were made on purified whole HIV-1 virions and primary T-lymphocytes. Viral particles had a largely negative surface charge, and lacked the regions of positivity near neutral pH that were observed with trimeric Env. T cells changed their surface chemistry as a function of activation state, becoming more negative over a wider range of pH after activation. Soluble recombinant CD4 (sCD4) was found to be positively charged under a wide range of conditions. Binding studies between sCD4 and gp140 show that the affinity of CD4-gp140 interactions depends on pH.ConclusionsTaken together, these findings allow a more complete model of the electrochemical forces involved in HIV-1 Env functionality. These results indicate that the influence of the localized environment on the interactions of HIV with target cells are more pronounced than previously appreciated. There is differential chemistry of trimeric, but not monomeric, Env under conditions which mimic the mucosa compared to those found systemically. This should be taken into consideration during design of immunogens which targets virus at mucosal portals of entry.
Highlights
Interactions between the HIV-1 envelope glycoprotein (Env) and its primary receptor CD4 are influenced by the physiological setting in which these events take place
The titration technique used in dynamic electrophoretic fingerprint (DEF) allows additional modeling of the charge characteristics and by implication altered conformational states not discernable with fixed crystal models. We have modeled these changes across salinities and pH ranges relevant to the physiological environments associated with mucosal transmission and systemic infection
Dynamic electrophoretic fingerprint of monomeric BX08 gp120 Initial studies were performed to determine the electrophoretic mobility (EM) of recombinant monomeric gp120 derived from the clade B HIV-1 strain BX08
Summary
Interactions between the HIV-1 envelope glycoprotein (Env) and its primary receptor CD4 are influenced by the physiological setting in which these events take place. Three discrete events occur: an outward density shift, a gp120 tilt away from the central z-axis, and a gp120 rotation which flattens the trimer ostensibly allowing the fusion peptide to protrude and insert into the host membrane [13]. These changes to gp120 structure promote interaction with one of two chemokine receptors, either CCR5 or CXCR4 (R5- and X4-, respectively) [14,15,16,17] triggering extensive conformational rearrangement in gp facilitating subsequent membrane fusion [18,19]
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