Did cyclodextrin glycosyltransferases evolve from alpha-amylases?

The hydrolytic enzymes, alpha-amylases, and the cyclodextrin glycosyltransferases (CGTases) are key enzymes in the depolymerization of starch. These two groups of enzymes are evolutionarily related. We propose that the transferase activity is likely to have evolved from an ancestral hydrolase. Sequence analysis provides support for this hypothesis. Consequently, we have conducted an experimental study to test the possible adaptive value for evolving a CGTase. We found that when an alpha-amylase and a CGTase are combined more glucose is generated from starch than would be expected from the independent action of either of these enzymes. Thus, we propose that the biological role of CGTases is to work in concert with alpha-amylases for the efficient saccharification of starch. This observation can be useful in industrial processes aimed at producing syrups with high contents of glucose or maltose. (C) 1997 Federation of European Biochemical Societies.