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  • Title: Structural elements responsible for the glucosidic linkage-selectivity of a glycoside hydrolase family 13 exo-glucosidase.
    Author: Saburi W, Rachi-Otsuka H, Hondoh H, Okuyama M, Mori H, Kimura A.
    Journal: FEBS Lett; 2015 Mar 24; 589(7):865-9. PubMed ID: 25728274.
    Abstract:
    Glycoside hydrolase family 13 contains exo-glucosidases specific for α-(1→4)- and α-(1→6)-linkages including α-glucosidase, oligo-1,6-glucosidase, and dextran glucosidase. The α-(1→6)-linkage selectivity of Streptococcus mutans dextran glucosidase was altered to α-(1→4)-linkage selectivity through site-directed mutations at Val195, Lys275, and Glu371. V195A showed 1300-fold higher kcat/Km for maltose than wild-type, but its kcat/Km for isomaltose remained 2-fold higher than for maltose. K275A and E371A combined with V195A mutation only decreased isomaltase activity. V195A/K275A, V195A/E371A, and V195A/K275A/E371A showed 27-, 26-, and 73-fold higher kcat/Km for maltose than for isomaltose, respectively. Consequently, the three residues are structural elements for recognition of the α-(1→6)-glucosidic linkage.
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