Genetic divergence among the group B coxsackieviruses

As documented in the preceding discussion, the noncoding regions, and in particular the 5' NTR, of the CVB are tolerant of a substantial degree of nucleotide diversity while still being capable of fulfilling the life cycle requirements for these viruses. While diversity among the CVB is observed in the sequences encoding for the capsid proteins, it tends to involve predominantly those regions coding for amino acids located at the surface of the virus and not those responsible for the structural integrity of the mature virion, i.e., beta-barrels and alpha-helices. It is these capsid surface differences that define the six serotypes of the CVB and subdivide them antigenically into strains. Additionally, these proteins most likely play the major role in determining host and cellular tropism. The most conserved of the CVB proteins and, therefore those with the least diversity in their coding sequences, appear to be the nonstructural proteins. Perhaps, as speculated earlier, it is a conformational requirement imposed by the necessity to interact with host or viral substrates that maintains the high degree of amino acid identity of this group of viral proteins.