Functional analysis of N-terminal domain of endoinulinase from Arthrobacter sp.S37

Abstract

N-terminal domain (NTD) of endoinulinase (EnIAb) for Arthrobacter sp. S37 is unique compared to other members in family 32 glycosidase. Chimeric exoinulinase (ChEX) fused with NTD of EnIAb induced complete dimerization of exoinulinase, while exoinulinase (ExIB) existed totally as a monomer. Dimerization of ChEX accompanied with drastic increase of the kcat for inulin and relatively smaller rise for sucrose. The enzyme efficiencies (kcat/Km) of ChEX toward inulin and sucrose were approximately 5-fold and 3-fold higher than those of ExIB, respectively. The enzyme activity ratio toward inulin and sucrose (I/S) was changed also from 0.75 to 1.24 by dimerization. Those results indicated that the newly introduced NTD-EnIAb to ExIB changed more effective to inulin than sucrose. In comparision with optimal enzyme reaction conditions of ExIB, the optimal pH of ChEX shifted from pH 7 to pH 5.5 and optimal temperature of ChEX shifted from 50 ℃ to 40 ℃.