Schaller Research Group at the University of Heidelberg and the German Cancer Research Center, Heidelberg, Germany.
Department of Infectious Diseases, Virology, University of Heidelberg, Heidelberg, Germany.
J Virol. 2019 Jan 4;93(2). doi: 10.1128/JVI.01581-18. Print 2019 Jan 15.
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. 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.
最近开发的人类诺如病毒细胞培养系统表明，胆汁的存在增强了或成为某些基因型生长的必要条件。在此发现之前，组织血型抗原（HBGA）是人类诺如病毒唯一研究充分的辅助因子，有证据表明，几种基因型与 HBGA 的结合能力较差。因此，本研究旨在研究人类诺如病毒衣壳如何与胆汁酸相互作用。我们发现，胆汁酸对 GII.1、GII.10 和 GII.19 衣壳的亲和力较低，但不与 GI.1、GII.3、GII.4 或 GII.17 结合。我们通过 X 射线晶体学显示，胆汁酸结合在诺如病毒衣壳突出（P）结构域的一个部分保守口袋上。氨基酸序列比对和结构分析提供了选择性胆汁酸结合的解释。有趣的是，我们发现，胆汁酸的结合是稳定几个 P 结构域环的关键步骤，这些环最佳地放置了一个必需的氨基酸侧链（Asp375），以在 otherwise HBGA 非结合物（GII.1）中结合 HBGA。此外，胆汁酸增强了已知的 HBGA 结合物（GII.10）的 HBGA 结合。总之，这些新数据表明，胆汁酸作为一种环稳定调节剂和增强剂，对某些诺如病毒基因型的 HBGA 结合起作用。鉴于人类诺如病毒病毒粒子在自然感染过程中可能与胆汁酸相互作用，我们的证据表明，在胆汁酸结合后，一种 HBGA 非结合物（GII.1）可以转化为 HBGA 结合物，这具有重要意义。我们的数据提供了直接证据，表明像 HBGA 一样，衣壳上的胆汁酸相互作用是某些基因型的重要辅助因子。然而，从这些新发现中似乎出现了更多未解答的问题。例如，胆汁酸的需求与某些基因型的流行之间是否存在关联？也就是说，GII.1 和 GII.10（胆汁酸结合物）基因型很少引起暴发，而 GII.4 和 GII.17 基因型（胆汁酸非结合物）则导致了大规模的流行。因此，似乎某些基因型需要胆汁酸，而其他基因型则在衣壳上改变了它们对胆汁酸的需求。
