Sequence similarities and evolutionary relationships of microbial, plant and animal α-amylases

Amino acid sequence comparison of 37 a-amylases from microbial, plant and animal sources was performed to identify their mutual sequence similarities in addition to the five already described conserved regions. These sequence regions were examined from structure/function and evolutionary perspectives. An unrooted evolutionary tree of a-amylases was constructed on a subset of 55 resi-dues from the alignment of sequence similarities along with conserved regions. The most important new information extracted from the tree was as follows: (a) the close evolutionary relationship of Alteromonas haloplanctis a-amylase (thermolabile enzyme from an antarctic psychrotroph) with the already known group of homologous a-amylases from streptomycetes, Thermomonospora cuwata, insects and mammals, and (b) the remarkable 40.1 % identity between starch-saccharifying Bacillus subtilis a-amylase and the enzyme from the ruminal bacterium Butyrivibrio fibrisolvens, an a-amylase with an unusually large polypeptide chain (943 residues in the mature enzyme). Due to a very high degree of similarity, the whole amino acid sequences of three groups of a-amylases, namely (a) fungi and yeasts, (b) plants, and (c) A. haloplanctis, streptomycetes, T cuwata, insects and mammals, were aligned independently and their unrooted distance trees were calculated using these alignments. Possible rooting of the trees was also discussed. Based on the knowledge of th