About Semblance Filtering in (Tau-P)-Domain

ABSTRACT A recently developed human norovirus cell culture system revealed that the presence of bile enhanced or was an essential requirement for the growth of certain genotypes. Before this discovery, histo-blood group antigens (HBGAs) were the only well-studied cofactor known for human noroviruses, and there was evidence that several genotypes poorly bound HBGAs. Therefore, the purpose of this study was to investigate how human norovirus capsids interact with bile acids. We found that bile acids had low-micromolar affinities for GII.1, GII.10, and GII.19 capsids but did not bind GI.1, GII.3, GII.4, or GII.17. We showed that bile acid bound at a partially conserved pocket on the norovirus capsid-protruding (P) domain using X-ray crystallography. Amino acid sequence alignment and structural analysis delivered an explanation of selective bile acid binding. Intriguingly, we discovered that binding of the bile acid was the critical step to stabilize several P domain loops that optimally placed an essential amino acid side chain (Asp375) to bind HBGAs in an otherwise HBGA nonbinder (GII.1). Furthermore, bile acid enhanced HBGA binding for a known HBGA binder (GII.10). Altogether, these new data suggest that bile acid functions as a loop-stabilizing regulator and enhancer of HBGA binding for certain norovirus genotypes. IMPORTANCE Given that human norovirus virions likely interact with bile acid during a natural infection, our evidence that an HBGA nonbinder (GII.1) can be converted to an HBGA binder after bile acid binding is of major significance. Our data provide direct evidence that, like HBGAs, bile acid interaction on the capsid is an important cofactor for certain genotypes. However, more unanswered questions seem to arise from these new discoveries. For example, is there an association between the bile acid requirement and the prevalence of certain genotypes? That is, the GII.1 and GII.10 (bile acid binders) genotypes rarely caused outbreaks, whereas the GII.4 and GII.17 genotypes (bile acid nonbinders) were responsible for large epidemics. Therefore, it seems plausible that certain genotypes require bile acids, whereas others have modified their bile acid requirements on the capsid.

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The P Domain of Norovirus Capsid Protein Forms a Subviral Particle That Binds to Histo-Blood Group Antigen Receptors

Journal of Virology ◽

10.1128/jvi.79.22.14017-14030.2005 ◽

2005 ◽

Vol 79 (22) ◽

pp. 14017-14030 ◽

Cited By ~ 148

Author(s):

Ming Tan ◽

Xi Jiang

Keyword(s):

Blood Group ◽

Receptor Binding ◽

Vaccine Development ◽

Human Colon ◽

Blood Group Antigen ◽

Antigen Receptors ◽

Human Colon Carcinoma Cell ◽

Strong Binding ◽

Internal Core ◽

P Domain

ABSTRACT Norovirus is the most important cause of nonbacterial acute gastroenteritis. We have shown previously that the isolated P domain containing the hinge forms a dimer and binds to histo-blood group antigen (HBGA) receptors with a low affinity (M. Tan, R. S. Hegde, and X. Jiang, J. Virol. 78:6233-6242, 2004). Here, we reported that the P domain of VA387 without the hinge forms a small particle with a significantly increased receptor binding affinity. An end-linked oligopeptide containing one or more cysteines promoted P-particle formation by forming intermolecular disulfide bridges. The binding sensitivity of the P particle to HBGAs was enhanced >700-fold compared to the P dimer, which was comparable to that of virus-like particles. The binding specificity of the P particle was further confirmed by strong binding to the Caco-2 cells, a human colon carcinoma cell line. This binding enhancement was observed in the P particles of both norovirus GI and GII strains. The P particle is estimated to contain 12 P dimers, in which the P2 subdomain builds up the outer layer, while the P1 subdomain forms the internal core. Taken together, our data indicate that the P domain is involved not only in dimerization but also in polymerization of the protein during the capsid assembling. The enhanced receptor binding of the P particle reflects the intrinsic feature of the viral capsid. The easy production of the P particle and its strong binding to HBGAs suggest that the P particle is useful in studying pathogenesis and morphogenesis of norovirus and candidates for antiviral or vaccine development.

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