Division of Cell and Molecular Biology, Department of Life Sciences, Imperial College London, London, United Kingdom.
J Virol. 2013 May;87(10):5318-30. doi: 10.1128/JVI.03151-12. Epub 2013 Mar 13.
We report the solution structures of the VPg proteins from feline calicivirus (FCV) and murine norovirus (MNV), which have been determined by nuclear magnetic resonance spectroscopy. In both cases, the core of the protein adopts a compact helical structure flanked by flexible N and C termini. Remarkably, while the core of FCV VPg contains a well-defined three-helix bundle, the MNV VPg core has just the first two of these secondary structure elements. In both cases, the VPg cores are stabilized by networks of hydrophobic and salt bridge interactions. The Tyr residue in VPg that is nucleotidylated by the viral NS7 polymerase (Y24 in FCV, Y26 in MNV) occurs in a conserved position within the first helix of the core. Intriguingly, given its structure, VPg would appear to be unable to bind to the viral polymerase so as to place this Tyr in the active site without a major conformation change to VPg or the polymerase. However, mutations that destabilized the VPg core either had no effect on or reduced both the ability of the protein to be nucleotidylated and virus infectivity and did not reveal a clear structure-activity relationship. The precise role of the calicivirus VPg core in virus replication remains to be determined, but knowledge of its structure will facilitate future investigations.
我们报告了猫杯状病毒（FCV）和鼠诺如病毒（MNV）VPg 蛋白的溶液结构，这些结构是通过核磁共振波谱法确定的。在这两种情况下，蛋白质的核心都采用了紧凑的螺旋结构，两端为灵活的 N 端和 C 端。值得注意的是，虽然 FCV VPg 的核心包含一个定义明确的三螺旋束，但 MNV VPg 核心只有前两个这些二级结构元件。在这两种情况下，VPg 核心都通过疏水和盐桥相互作用网络稳定。在病毒 NS7 聚合酶（FCV 中的 Y24，MNV 中的 Y26）核苷酸化的 VPg 中的 Tyr 残基位于核心的第一个螺旋内的保守位置。有趣的是，鉴于其结构，VPg 似乎无法与病毒聚合酶结合，从而将该 Tyr 置于活性部位，而无需 VPg 或聚合酶发生重大构象变化。然而，破坏 VPg 核心稳定性的突变对蛋白的核苷酸化能力和病毒感染力没有影响或降低，并且没有揭示明确的结构-活性关系。杯状病毒 VPg 核心在病毒复制中的精确作用仍有待确定，但对其结构的了解将有助于未来的研究。
