3.3 | Analysis of amino acid mutations
In this study, the amino acid mutations of the VP2 protein were identified, and the amino acid sequences of 44 isolates were compared with reference strains (Table 2). The results showed that 43 isolates had Phe267Tyr and Tyr324Ile mutations, and all new CPV-2a and new CPV-2b strains identified in this study had the Thr440Ala substitution. The substitutions of Ala5Gly and Gln370Arg were found in all CPV-2c subtype isolates, which have been reported to be specific to the CPV-2c virus (Geng et al., 2015). Of the 31 CPV-2c strains, only one showed a unique substitution on Arg481Lys. Residue 481 is located in the greatest variable GH loop (loops 3 and 4), comprising aa 267–498 of the VP2 protein (Agbandje, Parrish*, & Rossmann, 1995).