Sequence of archaealMethanococcus jannaschii α-amylase contains features of families 13 and 57 of glycosyl hydrolases: A trace of their common ancestor?
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Two sequentially different, seemingly unrelated α-amylase families exist, known as family-13 and family-57 glycosyl hydrolases. Despite the common enzyme activity, it has as yet been impossible to detect any sequence similarity between the two families. The detailed analysis of the recently determined sequence of the α-amylase from methanogenic archaeonMethanococcus jannaschii using the sensitiveHydrophobic Cluster Analysis method revealed that this α-amylase contains features of both families of α-amylases. Thus theM. jannaschii α-amylase is similar to thePyrococcus furiosus α-amylase from family 57 while it obviously contains most of the sequence fingerprints characteristic for α-amylase family 13. Importantly, a glutamic acid residue equivalent with the family-13 catalytic glutamate positioned in the β5-strand segment was identified in members of family 57. The results presented in this report indicate that the two families, 13 and 57, are either the products of a very distant common ancestor or have evolved from each other, although at present they can represent two different α-amylase families with evolved different catalytic mechanisms, catalytic machinery and folds.
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