Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan, USA.
J Virol. 2014 Apr;88(8):4543-57. doi: 10.1128/JVI.03685-13. Epub 2014 Feb 5.
New human norovirus strains emerge every 2 to 3 years, partly due to mutations in the viral capsid that allow escape from antibody neutralization and herd immunity. To understand how noroviruses evolve antibody resistance, we investigated the structural basis for the escape of murine norovirus (MNV) from antibody neutralization. To identify specific residues in the MNV-1 protruding (P) domain of the capsid that play a role in escape from the neutralizing monoclonal antibody (MAb) A6.2, 22 recombinant MNVs were generated with amino acid substitutions in the A'B' and E'F' loops. Six mutations in the E'F' loop (V378F, A382K, A382P, A382R, D385G, and L386F) mediated escape from MAb A6.2 neutralization. To elucidate underlying structural mechanisms for these results, the atomic structure of the A6.2 Fab was determined and fitted into the previously generated pseudoatomic model of the A6.2 Fab/MNV-1 virion complex. Previously, two distinct conformations, A and B, of the atomic structures of the MNV-1 P domain were identified due to flexibility in the two P domain loops. A superior stereochemical fit of the A6.2 Fab to the A conformation of the MNV P domain was observed. Structural analysis of our observed escape mutants indicates changes toward the less-preferred B conformation of the P domain. The shift in the structural equilibrium of the P domain toward the conformation with poor structural complementarity to the antibody strongly supports a unique mechanism for antibody escape that occurs via antigen flexibility instead of direct antibody-antigen binding.
Human noroviruses cause the majority of all nonbacterial gastroenteritis worldwide. New epidemic strains arise in part by mutations in the viral capsid leading to escape from antibody neutralization. Herein, we identify a series of point mutations in a norovirus capsid that mediate escape from antibody neutralization and determine the structure of a neutralizing antibody. Fitting of the antibody structure into the virion/antibody complex identifies two conformations of the antibody binding domain of the viral capsid: one with a superior fit and the other with an inferior fit to the antibody. These data suggest a unique mode of antibody neutralization. In contrast to other viruses that largely escape antibody neutralization through direct disruption of the antibody-virus interface, we identify mutations that acted indirectly by limiting the conformation of the antibody binding loop in the viral capsid and drive the antibody binding domain into the conformation unable to be bound by the antibody.
新的人类诺如病毒株每隔 2 到 3 年出现一次，部分原因是病毒衣壳的突变，使病毒能够逃避抗体中和和群体免疫。为了了解诺如病毒如何产生抗体耐药性，我们研究了诺如病毒逃避抗体中和的结构基础。为了确定在 MNV-1 衣壳突出（P）域中逃避中和单克隆抗体（MAb）A6.2 的特定残基，我们生成了 22 种具有 A'B'和 E'F'环中氨基酸取代的重组 MNV。E'F'环中的 6 个突变（V378F、A382K、A382P、A382R、D385G 和 L386F）介导了 MAb A6.2 中和的逃逸。为了阐明这些结果的潜在结构机制，我们确定了 A6.2 Fab 的原子结构，并将其拟合到先前生成的 A6.2 Fab/MNV-1 衣壳复合物的拟原子模型中。先前，由于两个 P 结构域环的灵活性，鉴定了 MNV-1 P 结构域的两个独特构象，A 和 B。观察到 A6.2 Fab 与 MNV P 结构域 A 构象的超优立体化学拟合。对我们观察到的逃逸突变体的结构分析表明，该结构向 P 结构域的不太优选的 B 构象发生变化。P 结构域结构平衡向与抗体结构互补性差的构象的转移强烈支持一种独特的抗体逃逸机制，该机制通过抗原灵活性而不是直接的抗体-抗原结合发生。
人类诺如病毒导致全球大部分非细菌性胃肠炎。新的流行株部分是由于病毒衣壳突变导致抗体中和逃逸而产生的。在此，我们鉴定了诺如病毒衣壳中的一系列点突变，这些突变介导了抗体中和的逃逸，并确定了中和抗体的结构。将抗体结构拟合到衣壳/抗体复合物中，确定了病毒衣壳抗体结合域的两种构象：一种具有更好的拟合度，另一种具有较差的拟合度。这些数据表明了一种独特的抗体中和模式。与其他主要通过直接破坏抗体-病毒界面来逃避抗体中和的病毒不同，我们鉴定了通过限制病毒衣壳中抗体结合环的构象并将抗体结合域驱动到无法与抗体结合的构象的突变。
