Role of the Carbohydrate Moiety of a Glucoamylase fromAspergillus awamorivar.kawachiin the Digestion of Raw Starch

Abstract

The digestion of raw starch by a glucoamylase (GA MU-H) from a mutant strain of Aspergillus awamori var. kawachi was closely correlated with mannoside chains O-linked to the Gp-I region (A470-V514), but not sugar chains N-linked to catalytic GAI' domain of GA MU-H. The partial replacement of mannose residues by glucose residues led to a significant decrease raw starch digestion. By the substitution of D2O for H2O in the reaction mixture, the raw starch digestion of GA MU-H decreased to 80% of that at 30 degrees C, although the rate of hydrolysis of soluble starch by and the ability to bind beta-cyclodextrin of GA MU-H were unchanged. Glycerol, known as an antichaotropic reagent, decreased the raw starch digestion of GA MU-H significantly. However, it did not have any effect on the enzymatic activity for soluble starch when soluble starch was the substrate. The efficient digestion of raw starch with raw starch-digesting glucoamylase needed the mannoside chains O-linked to the Gp-I region, which were suggested to contribute to digestion of raw starch through the interaction with water.

ProteinO-Glycosylation in Fungi: Diverse Structures and Multiple Functions

“…43,48,90) The O-glycans in Gp-I have been found to be responsible for enzyme stability, protection from proteolytic degradation, and enhanced activity towards raw starch. 51,[91][92][93] Furthermore, the polypeptide of the Gp-I domain is absolutely required for the secretion of GAI through the correct folding of the catalytic and starch-binding domains in the ER. 94) In the pmtA disruptant of A. awamori, GAI is underglycosylated, with reductions in the 6 kDa corresponding to 55% of the total O-glycans.…”

Production of multiple extracellular enzyme activities by novel submerged culture of Aspergillus kawachii for ethanol production from raw cassava flour

“…Glucoamylase and acid-stable -amylase from A. kawachii have granular starch-hydrolyzing activity [4,7], and are important industrial enzymes used to produce products such as bio-ethanol from starch substrates derived from grains and cereals. However, production of acid-stable -amylase by submerged culture is problematic because acid-stable -amylase is recognized as a solid-state culturespeciWc product [16], and to our knowledge, no reports have been published on the simultaneous production of glucoamylase and acid-stable -amylase by standard submerged culture of A. kawachii.…”

Thr/Ser-rich Domain ofAspergillusGlucoamylase Is Essential for Secretion

“…The Olinked oligosaccharides in Gp-I were found to be responsible for enzyme stability and enhanced activity on raw starch. 3,4) Furthermore, the deletion of Gp-I in the GAI molecule resulted in reduced secretion when GAI was heterologously expressed in yeast cells.…”