Ea. Macgregor, RELATIONSHIPS BETWEEN STRUCTURE AND ACTIVITY IN THE ALPHA-AMYLASE FAMILY OF STARCH-METABOLIZING ENZYMES, Starke, 45(7), 1993, pp. 232-237
Alpha-amylases are known to be multidomain proteins, i. e., the molecu
les consist of several folding units. Each alpha-amylase is believed,
however, to have a catalytic domain consisting of a barrel of eight pa
rallel beta-strands surrounded by eight alpha-helices, with an extra h
elix inserted after the sixth beta-strand. The beta-strands and helice
s alternate along the polypeptide chain and are linked together by irr
egular loops. Amino acid residues situated on the loops joining the C-
terminal end of each beta-strand to the N-terminal end of the followin
g helix make up the active site of the enzymes. A similar structure ha
s been found in cyclodextrin glucanotransferases and it is now believe
d that such a (beta/alpha)8-barrel also constitutes the catalytic doma
in of enzymes active on alpha-1,6-glucosidic bonds, and of enzymes wit
h dual specificity for both alpha-1,4- and alpha-1,6- bonds. Knowledge
of the three-dimensional structure of alpha-amylases and cyclodextrin
glucanotransferase has made possible identification of structural fea
tures important for enzymic activity and specificity. By analogy, some
general conclusions are reached concerning pullulanase, isoamylase, o
ligo-1,6-glucosidase, neopullulanase and branching enzymes.