Ji Xiaoyun, Axford Danny, Owen Robin, Evans Gwyndaf, Ginn Helen M, Sutton Geoff, Stuart David I
Division of Structural Biology, The Wellcome Trust Centre for Human Genetics, University of Oxford, Roosevelt Drive, Oxford, Oxfordshire OX3 7BN, United Kingdom.
Diamond House, Diamond Light Source, Harwell Science & Innovation Campus, Didcot, Oxfordshire OX11 0DE, United Kingdom.
J Struct Biol. 2015 Oct;192(1):88-99. doi: 10.1016/j.jsb.2015.08.009. Epub 2015 Aug 18.
Polyhedra represent an ancient system used by a number of insect viruses to protect virions during long periods of environmental exposure. We present high resolution crystal structures of polyhedra for seven previously uncharacterised types of cypoviruses, four using ab initio selenomethionine phasing (two of these required over 100 selenomethionine crystals each). Approximately 80% of residues are structurally equivalent between all polyhedrins (pairwise rmsd ⩽ 1.5 Å), whilst pairwise sequence identities, based on structural alignment, are as little as 12%. These structures illustrate the effect of 400 million years of evolution on a system where the crystal lattice is the functionally conserved feature in the face of massive sequence variability. The conservation of crystal contacts is maintained across most of the molecular surface, except for a dispensable virus recognition domain. By spreading the contacts over so much of the protein surface the lattice remains robust in the face of many individual changes. Overall these unusual structural constraints seem to have skewed the molecule's evolution so that surface residues are almost as conserved as the internal residues.
多面体是许多昆虫病毒用来在长时间环境暴露期间保护病毒粒子的一种古老系统。我们展示了七种以前未表征的质型多角体病毒类型的多面体的高分辨率晶体结构，其中四种使用从头硒代甲硫氨酸相位法（其中两种每种需要超过100个硒代甲硫氨酸晶体）。所有多角体蛋白之间约80%的残基在结构上是等效的（成对均方根偏差⩽1.5 Å），而基于结构比对的成对序列同一性低至12%。这些结构说明了在一个系统中4亿年进化的影响，在这个系统中，面对大量的序列变异性，晶格是功能上保守的特征。除了一个可有可无的病毒识别结构域外，晶体接触在大部分分子表面得以维持。通过将接触分布在如此多的蛋白质表面，晶格在面对许多个体变化时仍然稳健。总体而言，这些不寻常的结构限制似乎使分子的进化发生了偏差，以至于表面残基几乎与内部残基一样保守。
