Hydrolase and transferase activities of the beta-1,3-exoglucanase of Candida albicans.
The exo-beta-1,3-glucanase of Candida albicans (Exg) has a marked specificity for beta-1,3-glucosidic linkages as judged by the kinetic constants for p-nitophenyl beta-glucoside, beta-linked disaccharides of glucose (laminaribiose, gentiobiose, and cellobiose), oligosaccharides of the laminari series, laminarin and pustulan. The kcat/Km ratios for a series of laminari oligosaccharides from -biose to -heptaose showed that Exg has an extended substrate-binding site which contains at least five binding sites for sugar residues. Binding at position +2 (the third sugar residue) increases the kcat twofold while positions +3 and +4 lower the Km value further and thereby increase the catalytic efficiency. Exg catalyses an efficient transglucosylation reaction with high concentrations of laminari-oligosaccharides which specifically form beta-1,3 linkages and with yields up to 50%. The rate of the transglucosylation is concentration-dependent and can be more than 10 times faster than the hydrolytic reaction with excess donor substrates such as laminaritriose and laminarihexaose. The kinetics of Exg and the predicted substrate-binding site for up to five sugar residues are consistent with a recent structural analysis of the enzyme-binding site.
Stubbs
H J
HJ
Department of Chemistry, University of Otago, Dunedin, New Zealand.
Brasch
D J
DJ
Emerson
G W
GW
Sullivan
P A
PA
D001665:Binding Sites; D002176:Candida albicans / Q000201:enzymology*; D002240:Carbohydrate Sequence; D043326:Glucan 1,3-beta-Glucosidase; D006026:Glycoside Hydrolases / Q000737:chemistry / Q000378:metabolism*; D006867:Hydrolases / Q000378:metabolism*; D007700:Kinetics; D008969:Molecular Sequence Data; D009844:Oligosaccharides / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D013379:Substrate Specificity; D014166:Transferases / Q000378:metabolism*
D009844:Oligosaccharides; D014166:Transferases; D006867:Hydrolases; D006026:Glycoside Hydrolases; D043326:Glucan 1,3-beta-Glucosidase; C117648:beta-1,3-exoglucanase