SEQUENCE SIMILARITIES AND EVOLUTIONARY RELATIONSHIPS OF MICROBIAL, PLANT AND ANIMAL ALPHA-AMYLASES

Amino acid sequence comparison of 37 alpha-amylases from microbial, pl ant and animal sources was performed to identify their mutual sequence similarities in addition to the five already described conserved regi ons. These sequence regions were examined from structure/function and evolutionary perspectives. An unrooted evolutionary tree of alpha-amyl ases was constructed on a subset of 55 residues 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 alpha-amylase ( thermolabile enzyme from an antarctic psychrotroph) with the already k nown group of homologous alpha-amylases from streptomycetes, Thermomon ospora curvata, insects and mammals, and (b) the remarkable 40.1% iden tity between starch-saccharifying Bacillus subtilis alpha-amylase and the enzyme from the ruminal bacterium Butyrivibrio fibrisolvens, an al pha-amylase with an unusually large polypeptide chain (943 residues in the mature enzyme). Due to a very high degree of similarity, the whol e amino acid sequences of three groups of alpha-amylases, namely (a) f ungi and yeasts, (b) plants, and (c) A. haloplanctis, streptomycetes, T. curvata, insects and mammals, were aligned independently and their unrooted distance trees were calculated using these alignments. Possib le rooting of the trees was also discussed. Based on the knowledge of the location of the five disulfide bonds in the structure of pig pancr eatic alpha-amylase, the possible disulfide bridges were established f or each of these groups of homologous alpha-amylases.