The Basic Architecture of Viruses.

Viruses are elegant macromolecular assemblies and constitute a paradigm of the economy of genomic resources; they must use simple general principles to complete their life cycles successfully. Viruses need only one or a few different capsid structural subunits to build an infectious particle, which is possible for two reasons: extensive use of symmetry and built-in conformational flexibility. Although viruses come in many shapes and sizes, two major symmetric assemblies are found: icosahedral and helical. The enormous diversity of virus structures appears to be derived from one or a limited number of basic schemes that became more complex by consecutive incorporation of additional structural elements. The intrinsic structural polymorphism of the viral proteins results in dynamic capsids. The study of virus structures is required to understand structure-function relationships, including those related to morphogenesis and antigenicity, among many others. These structural foundations can be extended to other macromolecular complexes that control many fundamental processes in biology.