Pm. Coutinho et Pj. Reilly, STRUCTURE-FUNCTION-RELATIONSHIPS IN THE CATALYTIC AND STARCH BINDING DOMAINS OF GLUCOAMYLASE, Protein engineering, 7(3), 1994, pp. 393-400
Sixteen primary sequences from five sub-families of fungal, yeast and
bacterial glucoamylases were related to structural information from th
e model of the catalytic domain of Aspergillus awamori var. X100 gluco
amylase obtained by protein crystallography. This domain is composed o
f thirteen cr-helices, with five conserved regions defining the active
site. Interactions between methyl or-maltoside and active site residu
es were modelled, and the importance of these residues on the catalyti
c action of different glucoamylases was shown by their presence in eac
h primary sequence. The overall structure of the starch binding domain
of some fungal glucoamylases was determined based on homology to the
C-terminal domains of Bacillus cyclodextrin glucosyltransferases. Crys
tallography indicated that this domain contains 6-8 beta-strands and h
omology allowed the attribution of a disulfide bridge in the glucoamyl
ase starch binding domain. Glucoamylase residues Thr525, Asn530 and Tr
p560, homologous to Bacillus stearothemophilus cyclodextrin glucosyltr
ansferase residues binding to maltose in the C-terminal domain, could
be involved in raw-starch binding. The structure and length of the lin
ker region between the catalytic and starch binding domains in fungal
glucoamylases can vary substantially, a further indication of the func
tional independence of the two domains.