Infectious bronchitis virus S2 gene sequence variability may affect S1 subunit specific antibody binding

The S2 gene of several strains of infectious bronchitis virus (IBV) belongi ng to the Arkansas, Connecticut, and Florida serotypes was sequenced. Phylo genetic analysis of the S2 gene nucleotide and deduced amino acid sequence data resulted in groups of strains that were the same as groupings observed when S1 sequence data was used. Thus, it appears that S2 subunits are cons erved within a serotype but not between serotypes. Although the sequence di fferences were small, we found that only a few amino acid differences were responsible for different secondary structure predictions for the S2 subuni t. It is likely that these changes create different interactions between th e S1 and S2 subunits, which could affect the conformation of the S1 subunit where serotype specific epitopes are located. Based on this sequence data, we hypothesize that the S2 subunit can affect specific antibody binding to the S1 subunit of the IBV spike glycoprotein.