Mesophilic substitutions at the structurally equivalent positions of significant amino acid types in thermophiles for the (α/β)
fold based on pairwise structural alignments. Statistically significant amino acid types are (A) arginine, (B) leucine, and (C) proline. Structurally equivalent positions of aligned amino acids between mesophilic endoglucanases and their structurally similar thermophilic counterpart were analyzed for substitutions. The x-axis shows the type or class of amino acids substituted in mesophiles. The count of substitution sites is plotted as a histogram for the following pair shown in Figure 3A: Clostridium thermocellum (Cα trace colored in red, pdb id: 2e4t) and mesophile Clostridium acetobutylicum (Cα trace colored in blue, pdb id: 3ik2). Positions of the amino acids are shown in CPK model in superimposed protein structures, where they are differentially colored with respect to atom type.