Establishment of mesophilic-like catalytic properties in a thermophilic enzyme without affecting its thermal stability.

Thermophilic enzymes are generally more thermally stable but are less active at moderate temperatures than are their mesophilic counterparts. Thermophilic enzymes with improved low-temperature activity that retain their high stability would serve as useful tools for industrial processes especially when robust biocatalysts are required. Here we show an effective way to explore amino acid substitutions that enhance the low-temperature catalytic activity of a thermophilic enzyme, based on a pairwise sequence comparison of thermophilic/mesophilic enzymes.

Robustness of predictions of extremely thermally stable proteins in ancient organisms.

A number of studies have addressed the environmental temperatures experienced by ancient life. Computational studies using a nonhomogeneous evolution model have estimated ancestral G + C contents of ribosomal RNAs and the amino acid compositions of ancestral proteins, generating hypotheses regarding the mesophilic last universal common ancestor. In contrast, our previous study computationally reconstructed ancestral amino acid sequences of nucleoside diphosphate kinases using a homogeneous model and then empirically resurrected the ancestral proteins.