부산대학교 도서관

Abstract: Rice Os4BGlu12 β-glucosidase is a family 1 glycoside hydrolase, the transcript levels of which have previously been found to be induced in response to herbivore attack and salinity stress. Here, high levels of Os4bglu12 transcripts were also detected in the shoot during germination, in the leaf sheath and stem of mature rice plants under normal growth conditions. The transcripts of this gene were up-regulated in response to wounding, methyl jasmonate and ethephon in 10-day-old rice seedlings. Os4BGlu12 expressed in recombinant Escherichia coli hydrolyzed β-(1,3;1,4)-glucooligosaccharides generated by the wounding-induced rice endo-(1,3;1,4)-β-glucanase OsEGL1, suggesting that both enzymes may act in concert in remodeling of damaged cell wall. Among oligosaccharides tested, Os4BGlu12 hydrolyzed β-(1,4)-linked glucooligosaccharides with highest catalytic efficiency (k cat /K m =2.7–4.9s−1 mM−1) when the degree of polymerization ranged from 3 to 6. It also hydrolyzed the β-(1,3)-linked disaccharide laminaribiose with high catalytic efficiency (k cat/K m =4.5s−1 mM−1). Among the natural glycosides tested, Os4BGlu12 efficiently hydrolyzed deoxycorticosterone 21-glucoside (k cat/K m =20s−1 mM−1) and apigenin 7-O-β-d-glucoside (k cat/K m =6.7s−1 mM−1). The amino acid residues predicted to line the active site of Os4BGlu12 are more similar to those of cyanogenic and flavonoid β-glucosidases than oligosaccharide hydrolases, and it may function in defense, as well as in cell wall-derived oligosaccharide break-down. [Copyright &y& Elsevier]