Human Norovirus Neutralized by a Monoclonal Antibody Targeting the HBGA Pocket

Abstract

22Temporal changes in the GII.4 human norovirus capsid sequences occasionally result 23 in the emergence of genetic variants capable of causing new epidemics. The GII.4 24 persistence is believed to be associated with the recognition of numerous histo-blood 25 group antigen (HBGA) types and antigenic drift. We found that one of the earliest 26 known GII.4 isolate (1974) and a more recent epidemic GII.4 variant (2012) had 27 varied norovirus-specific monoclonal antibody (MAb) reactivities, yet similar HBGA 28 binding profiles. To better understand the binding interaction of one MAb (10E9) that 29 had varied reactivities with these GII.4 variants, we determined the X-ray crystal 30 structure of the NSW-2012 GII.4 P domain 10E9 Fab complex. We showed that the 31 10E9 Fab interacted with conserved and variable residues, which could be associated 32 with antigenic drift. Interestingly, the 10E9 Fab binding pocket partially overlapped 33 the HBGA pocket and had direct competition for conserved HBGA binding residues 34 (i.e., Arg345 and Tyr444). Indeed, the 10E9 MAb blocked norovirus VLPs from 35 binding to several sources of HBGAs. Moreover, the 10E9 antibody completely 36 abolished virus replication in the human norovirus intestinal enteroid cell culture 37 system. Our new findings provide first direct evidence that competition for GII.4 38 HBGA binding residues and steric obstruction could lead to norovirus neutralization. 39On the other hand, the 10E9 MAb recognized residues flanking the HBGA pocket, 40 which are often substituted as the virus evolves. This mechanism of antigenic drift 41 likely influences herd immunity and impedes the possibility of acquiring broadly 42 reactive HBGA-blocking antibodies. 43 3 IMPORTANCE 44 45

Immunological Cross-Reactivity of an Ancestral and the Most Recent Pandemic Norovirus GII.4 Variant

“…However, some amino acids, such as 294 and 373 in the epitope A [ 23 , 26 ] and 310 in the NERK motif [ 31 ], shared between GII.4 1999 and GII.4 2006 VLPs might have greater impact on cross-blocking responses than other amino acids. In addition to blocking epitopes discussed here, other epitopes affecting the blocking responses have been published [ 28 , 29 ] and there could be other yet undiscovered regions impacting the cross-blocking responses.…”

“…Virions are dynamic structures reacting to environment with conformational changes, which enable biologically relevant functions such as receptor/ligand binding [ 27 ]. Mutations in the virion core, or neutralizing antibody binding to certain epitopes, can sterically block receptor binding site or cause conformational change in distant epitopes impairing ligand interactions [ 27 , 28 , 29 ]. Some of the highly variable blocking epitopes of NoV GII.4 are exposed on the surface of P2-domain (e.g., epitopes A and D) while others, like epitope F, are buried and broadly conserved [ 25 ].…”

Heterologous expression of human norovirus GII.4 VP1 leads to assembly of T=4 virus-like particles

“…GII.4 VLPs and their corresponding P domains have been extensively examined for binding to co-factors (HBGAs and bile acid), antibodies, human milk oligosaccharides (HMOs), and Nanobodies (21,31,37,(39)(40)(41). NSW-2012 P domains were capable of binding numerous HBGA types and the VLPs cross-reacted with Nanobodies and antibodies that were raised against other genotypes or GII.4 variants.…”