Genetic characterization of type A foot-and-mouth disease virus 3A region in context of the reemergence of VP359-deletion lineage in India.

The 3A region of foot-and-mouth disease virus has been implicated in host range and virulence. Here we analyzed the 3A region of serotype A virus in view of the emergence of a variant group in India with an amino acid deletion at an antigenically critical position of capsid protein, VP3. The 3A region exhibited extreme variability with 38% of the amino acid positions showing substitutions and the C-terminal third (127-151) region was most flexible. Genotype inclusive grouping of type A foot-and-mouth disease virus as observed in 1D region based phylogeny was much less apparent at 3A region possibly due to independent evolution of nonstructural and structural protein coding regions. Akin to the 1D region, the VP3(59)-deletion group maintained its phylogenetic distinctness even at the 3A region and was found to be diverging with time. Twelve lineage specific signature amino acid residues, of which four were identified to be experiencing positive selection, indicates fixation of advantageous mutations in a lineage specific manner. Six positions, all located in the hypervariable C-terminal third, were identified to be under positive selection and were presumed to be imparting the virus certain advantage accounting for its adaptability to wide host spectrum and rapid dissemination. A significant change of Q(44)H was noted only in the older lineage (VIIb) of the deletion group at a position where Q(44)R mutation is associated with guinea pig adaptation. As this site has been detected to be under positive selection, such a lineage specific substitution is thought to have imparted certain temporary advantage to the virus during its possible adaptation in wild or some understudied domestic hosts and must not have seriously compromised fitness upon readaptation in bovines. A conserved hydrophobic transmembrane domain from position 59 to 76 could be predicted which possibly anchors 3A to intracellular membranes for successful interaction with RNA replication complex.