MUTATIONS TO ALTER ASPERGILLUS-AWAMORI GLUCOAMYLASE SELECTIVITY - I -TYR48PHE49-]TRP, TYR116-]TRP, TYR175-]PHE, ARG241-]LYS, SER411-]ALA AND SER411-]GLY
Ty. Fang et al., MUTATIONS TO ALTER ASPERGILLUS-AWAMORI GLUCOAMYLASE SELECTIVITY - I -TYR48PHE49-]TRP, TYR116-]TRP, TYR175-]PHE, ARG241-]LYS, SER411-]ALA AND SER411-]GLY, Protein engineering, 11(2), 1998, pp. 119-126
Glucoamylase mutations to reduce isomaltose formation from glucose con
densation and thus increase glucose yield from starch hydrolysis were
designed to produce minor changes in the active site at positions not
totally conserved. Tyr175-->Phe and Ser411-->Gly glucoamylases had cat
alytic efficiencies on DP 2-7 maltooligosaccharides like those of ,wil
d-type glucoamylase, while the catalytic efficiencies of Tyr116-->Trp,
Arg241-->Lys and Ser411-->Ala glucoamylases were reduced by about hal
f and Tyr48Phe49-->Trp glucoamylase had little remaining activity. Tyr
175-->Phe, Ser411-->Ala and Ser411-->Gly glucoamylases had decreased r
atios of the initial rate of isomaltose formation from glucose condens
ation to that of glucose formation from maltodextrin hydrolysis at bot
h 35 and 55 degrees C compared with wild-type glucoamylase. Arg241-->L
ys glucoamylase had a very similar ratio, while Tyr116-->Trp glucoamyl
ase had a higher ratio. The highest glucose yields from maltodextrin h
ydrolysis were by the mutant glucoamylases having the lowest ratios of
initial rates of isomaltose formation to glucose formation and this p
redicted high glucose yields better than the ratio of catalytic effici
ency for maltose hydrolysis to that for isomaltose hydrolysis.