Close evolutionary relatedness of alpha-amylases from archaea and plants

The amino acid sequences of 22 alpha-amylases from family 13 of glycosyl hy drolases were analyzed with the aim of revealing the evolutionary relations hips between the archaeal alpha-amylases and their eubacterial and eukaryot ic counterparts. Two evolutionary distance trees were constructed: (i) the first one based on the alignment of extracted best-conserved sequence regio ns (58 residues) comprising beta 2, beta 3, beta 4, beta 5, beta 7, and bet a 8 strand segments of the catalytic (alpha/beta)(8)-barrel and a short con served stretch in domain B protruding out of the barrel in the beta 3 --> a lpha 3 loop, and (ii) the second one based on the alignment of the substant ial continuous part of the (alpha/beta)(8)-barrel involving the entire doma in B (consensus length: 386 residues). With regard to archaeal a-amy lases, both trees compared brought, in fact, the same results; i.e., all family 1 3 alpha-amylases from domain Archaea were clustered with barley pi isozymes , which represent all plant alpha-amylases. The enzymes from Bacillus liche niformis and Escherichia coli, representing liquefying and cytoplasmic alph a-amylases, respectively, seem to be the further closest relatives to archa eal alpha-amylases. This evolutionary relatedness clearly reflects the disc ussed similarities in the amino acid sequences of these alpha-amylases, esp ecially in the best-conserved sequence regions. Since the results for alpha -amylases belonging to all three domains (Eucarya, Eubacteria, Archaea) off ered by both evolutionary trees are very similar, it is proposed that the i nvestigated con-served sequence regions may indeed constitute the "sequence fingerprints" of a given alpha-amylase.