Figure 4.

(A) Sequence alignment of the 12 triosephosphate isomerase structures investigated. The identified phylogenetic motifs, indicated by the black line above the first sequence, frequently correspond to those residues that are generally responsible for defining the catalytic Glu (highlighted in bold) pKa values. The three oxyanion hole residues are also highlighted in bold. Stabilizing interactions, which lower the pKa value, are colored light gray, whereas destabilizing interactions are dark gray. The order (top to bottom) of the proteins in the alignment is the same as in Figure 2A ▶ and Table 1. (B) Sequence alignment of the four enolase structures investigated. Again, phylogenetic motifs generally correspond to those residues that are responsible for the extreme pKa values in Glu211, Lys357, and Lys408 (highlighted in bold). The pKa value of His164 (also bold), which has also been suggested as a catalytic residue, is not as shifted as the other three potential catalytic candidates. Residues involved in the electrostatic network stabilizing the charged forms of the above residues are colored light gray. Inclusion in the electrostatic network is defined by a single pairwise interaction with one of the four residues above that is greater than ±1.0 kcal/mol or more than two interactions greater than ±0.5 kcal/mol. The order (top to bottom) of the proteins in the alignment is the same as in Figure 2B ▶ and Table 3.