University of California, San Diego, Department of Chemistry & Biochemistry, La Jolla, CA 92093, USA.
J Struct Biol. 2010 Apr;170(1):109-16. doi: 10.1016/j.jsb.2009.12.003. Epub 2009 Dec 4.
The capsids of large, icosahedral dsDNA viruses are built from well-ordered aggregates of capsomers, known as trisymmetrons and pentasymmetrons, which are centered on the icosahedral 3-fold and 5-fold axes, respectively. We derive the complete set of rules for constructing an icosahedral structure from these symmetrons when the T lattice symmetry is odd and show that there are three classes of solutions, each of which follows from a different relationship between the size of the pentasymmetron and the values of the h and k icosahedral lattice parameters. Together, these three classes account for all possible ways of building an icosahedral structure solely from trisymmetrons and pentasymmetrons. Also, every icosahedral lattice with odd T number has solutions from exactly two of these three classes, with the set of allowed classes dependent on which of the two lattice parameters is odd. For symmetric lattices (if h=k or h=0), the two solutions yield the same symmetron sizes, but when the lattice parameters are equal (h=k) the solutions can be distinguished by the relative orientations of the symmetrons. We discuss these results in the context of known virus structures and explore the implications for viruses whose structures have not yet been solved.
大型二十面体双链 DNA 病毒的衣壳由排列整齐的衣壳粒聚集而成，这些衣壳粒分别称为三聚体和五聚体，它们分别以二十面体的 3 重轴和 5 重轴为中心。当 T 晶格对称性为奇数时，我们从这些对称体中推导出构建二十面体结构的完整规则，并表明存在三类解，每一类都源于五聚体大小与 h 和 k 二十面体晶格参数值之间不同的关系。这三类共同构成了仅从三聚体和五聚体构建二十面体结构的所有可能方法。此外，奇数 T 数的每个二十面体晶格都有来自这三类中的两类的解，允许的类集取决于两个晶格参数中哪一个是奇数。对于对称晶格（如果 h=k 或 h=0），两个解给出相同的对称体大小，但当晶格参数相等（h=k）时，解可以通过对称体的相对取向来区分。我们在已知病毒结构的背景下讨论了这些结果，并探讨了尚未解决结构的病毒的意义。
