Further, the calculation of site-specific profiles on the basis of posterior analysis for all group pairs with functional divergence would predict the critical amino acid residues, which are accountable for the functional divergence. Among aligned sites, most of them had low posterior probabilities. Qk ≥ 0.80 and Qk ≥ 0.95 were utilized empirically as cutoffs to determine type I functional divergence-related residues existing between groups, so as to greatly reduce false positive (Wang et al., 2011). For most of pairs of groups, at least one site had the posterior probability higher than 0.8, and four pairs of groups had one site with posterior probability higher than 0.95 (Figure 6). A cut-off value Q(k) ≥ 0.95 was used for estimated key amino acid residues. The number of amino acid residues that presumably contributed to alter functional constraints was small between TPS groups. Three amino acid residues (669, 704, and 753) in all comparisons were identified as being most important for the functional divergence. These amino acids are all localized in the TPP domain.