Research On The Mechanism Of Norovirus And Oligosaccharide Binding

Human noroviruses(huNoVs)is responsible for almost a fifth of all acute gastroenteritis cases worldwide.affecting people of all age groups.It is characterized by vomiting,diarrhea,nausea,and low-grade fever.NoVs have genetic diversity that are classified into seven genogroups.GI and GII genogroups mainly infect human beings,and contain at least 35 genotypes according to the nomenclature of the capsid protein.GII genegroup causese the most prevalence in huNoVs,which has been identified 26 genotypes.huNoVs can recognize histo-blood group antigens(HBAGs)as attachment factors or receptors,affecting their host susceptibility.A large number of research have indentified that the glycan binding profiles of huNoVs are associated with their prevalence.The emergence of new epidemic strains,especially the development of rare strain into the mainstream strain often leads to changes in the glycan specificity.Therefore,it is necessary to comprehensive understand glycans feature of rare strains,eveloved new genotypes and outbreak strains,and elucidate the molecular basis of the change in the glycan binding.This research consisted of following three parts.GII.13 and GII.21 huNoVs form a unique genetic lineage that emerged from mainstream GII NoVs via development of a new,nonconventional glycan binding site(GBS)that binds Lewis a(Lea)antigen.In the glycans specificity,what are the advantages of the new GII.13/21 GBS that is different from traditional GII genotypes.In this study,we provide solid phenotypic and structural evidence indicating that this new GBS recognizes a group of glycans with a common terminal ?-galactose(?-Gal).First,we found that six kinds of P domain proteins of GII.13/21 huNoVs circulating at different times bound three glycans sharing a common terminal ?-Gal,including Lee,lactose,and mucin core 2.Second.we solved the cry'stal structures of the GII.13 P dimers in complex with Lee and mucin core 2.which showed that ?-Gal is the major binding saccharide.These indicate that GBS of GII.13/21 have a wide binding spectral.which is the advantage of its targeted population.Third,non-fat milk and lactose blocked the GII.13/21 P domain-glycan binding.This suggests that non-fat milk and lactose can act as decoy receptors to inhibit virus infection.which may explain the low prevalence of GII.13/21 viruses.In the winter of 2016-2017.the rare recombinant stain GII.P16-GII.2 broke out in many country,appeared together with GII.P16-GII.1.In previous reports.GII.2 and GII.1 did not bind HBGAs.and structural analysis showed that the orientation of Asp382 of capsid protein of GII.2 and Asp375 of capsid protein of GII.1 that combined with HBGAs occurd reverse.So.is there any change in the glycan receptor of GII.2 and GII.1 from the rare strains to the outbreak strain?In this study,we identified the glycan binding specifity of GII.2 capsid protein outbreak in the 2016 and GII.1 through a series of functional experiments and structure analysis.The structural analysis indicated that the orientation of Asp382 of GII.2 and Asp375 of GII.1 combined with the IIBGAs binding site were recovered conventionally orientated the HBGAs binding site.NoVs are RNA viruses and considered fast-evolving viruses.GII.23/24/25 are the recently reported the new NoV genotypes,but it's the glycan receptor binding characteristics and the molecular basis of their interactions are unclear.In this part.the binding specificity of GII.23/24/25 have been determined by saliva and glycan binding assay.It was found GII.23/24/25 bind to A or/and B saliva and H disaccharide antigen.The complex crystal structure of GII.25 and H disaccharide antigen indicated that the structural characteristics of it are similar to those of the traditional GII,for example,the binding site is located at the interface of P dimer,fucose act as the major binding saccharide.These results indicate that the evolutionary traits of new genetypes tends to interact with the characteristics of traditional GII genotype HBGAs under the evolution of norovirus GII genogroup in the pressure of natural selection.In conclusion,this study expanded the binding spectrum of GII.13/21 in GII genogroup by functional experiments and structural analysis,clarified its unique mechanism of binding to glycan antigen and the relationship with its epidemiological.It is also identified the binding specificity of the prevalent recombinant strain GII.P16-GII.2 and GII.P16-GII.1 and the genotypes GII.23/24/25.Our findings provide new insights into the outbreak mechanism and host interaction of huNoVs.which may facilitate development of strategies for vaccine and antiviral drug of huNoVs.