Global and local envelope protein dynamics of hepatitis C virus determine broad antibody sensitivity

Abstract

Broad antibody sensitivity differences of hepatitis C virus (HCV) isolates and their ability to persist in the presence of neutralizing antibodies (NAbs) remain poorly understood. Here, we show that polymorphisms within glycoprotein E2, including hypervariable region 1 (HVR1) and antigenic site 412 (AS412), broadly affect NAb sensitivity by shifting global envelope protein conformation dynamics between theoretical “closed,” neutralization-resistant and “open,” neutralization-sensitive states. The conformational space of AS412 was skewed toward β-hairpin–like conformations in closed states, which also depended on HVR1, assigning function to these enigmatic E2 regions. Scavenger receptor class B, type I entry dependency of HCV was associated with NAb resistance and correlated perfectly with decreased virus propensity to interact with HCV co-receptor CD81, indicating that decreased NAb sensitivity resulted in a more complex entry pathway. This link between global E1/E2 states and functionally distinct AS412 conformations has important implications for targeting AS412 in rational HCV vaccine designs.

An Entropic Safety Catch Controls Hepatitis C Virus Entry and Antibody Resistance

“…The latter pathway accounts for residual infection by WT virus in the absence of SR-B1 (Figure 1B & C). Whilst this model is supported by published data (Augestad et al, 2020; Kalemera et al, 2019; Prentoe et al, 2019), the mechanistic basis of SR-B1 mediated priming has, thus far, been unclear. To recapitulate the physical reality of virus entry, the model includes a variable that reflects the intrinsic instability of HCV particles.…”

“…The precise molecular basis of E2-receptor interactions have yet to be defined at the structural level; nonetheless, mutational and antibody blocking experiments have demonstrated that SR-B1 binding occurs via the N-terminal HVR-1, whilst the CD81 binding site is thought to be composed of three discontinuous regions (antigenic site 412 [AS412], the front layer, and the CD81 binding loop) (Kong et al, 2013; Owsianka et al, 2006; Scarselli et al, 2002). Previous work, including our own, suggests that SR-B1 is the initial receptor for HCV and is likely to prime subsequent stages of entry (including interaction with CD81) via an unknown mechanism (Augestad et al, 2020; Evans et al, 2007; Kalemera et al, 2019).…”

“…This originally led to the hypothesis that HVR-1 acts as a shield to occlude neutralising epitopes and the CD81 binding site. However, it has since become clear that the global nature of nAb sensitisation is not easily explained by a simple shielding model (Augestad et al, 2020; Prentoe et al, 2019). Moreover, many studies have noted that substitutions in E2, many arising during in vitro culture, confer altered SR-B1 dependency and sensitivity to neutralisation (Bitzegeio et al, 2010; Dhillon et al, 2010; Grove et al, 2008; Keck et al, 2009; Koutsoudakis et al, 2012; Lavie et al, 2014; Song et al, 2012).…”

“…al. have recently suggested that a conformational ‘opening’ of E1E2 may be regulated by SR-B1-HVR-1 interactions (Augestad et al, 2020). The HVR-1 safety catch model sufficiently rationalises all of the above observations.…”

“…al. have suggested that SR-B1 may trigger a conformational opening of E1E2, associated with changes in AS412 (a functional epitope directly downstream of HVR-1); although the structure of this ‘open’ state, and how it relates to E1E2 reactivity, remains unclear (Augestad et al, 2020). Alternatively, Tzarum et.…”