Lettuce is often implicated in human norovirus (HuNoV) foodborne outbreaks. We identified H-like histo-blood group antigens (HBGAs) on lettuce leaves as specific binding moieties for virus-like particles (VLPs) of HuNoV GII.4/HS194/2009 strain. The objective of this study was to determine whether HuNoV-lettuce binding is mediated through the virus HBGA binding sites (HBS). Toward this objective, VLPs of historical HuNoV GII.4 strains (1987, 1997, 2002, 2004 and 2006) with known natural mutations in their HBS, two newly generated VLP mutants of GII.4/HS194/2009 (D374A and G443A) and a VLP mutant (W375A) of GI.1/Norwalk/1968 along with its wild type VLPs, which displays distinct HBS, were investigated for their binding to lettuce. ELISA revealed that historical GII.4 strains binding to lettuce was dependent on their HBGAs profiles. The VLP mutants D374A and G443A lost binding to HBGAs and displayed no to minimal binding to lettuce, respectively. The VLPs of GI.1/Norwalk/1968 strain bound to lettuce through an H-like HBGA and the binding was inhibited by fucosidase digestion. Mutant W375A which was previously shown not to bind to HBGAs, displayed significantly reduced binding to lettuce. We conclude that the binding of HuNoV GII.4 and GI.1 strains to lettuce is mediated through the virus HBS.
Keywords: Foodborne viruses; H-like antigens; Histo-blood group antigens; Human norovirus; Lettuce; Virus-lettuce interactions; Virus-like particles; mutations; virus HBGA-binding sites.