Identification of rice Os4BGlu13 as a beta-glucosidase which hydrolyzes gibberellin A4 1-O-beta-D-glucosyl ester, in addition to tuberonic acid glucoside and salicylic acid derivative glucosides

摘要

Gibberellin 1-O-beta-D-glucose ester hydrolysis activity has been detected in rice seedling extracts, but no enzyme responsible for this activity has ever been purified and identified. Therefore, gibberellin A4 glucosyl ester (GA(4)-GE) beta-D-glucosidase activity was purified from ten-day rice seedling stems and leaves. The family 1 glycoside hydrolase Os4BGlu13 was identified in the final purification fraction. The Os4BGlu13 cDNA was amplified from rice seedlings and expressed as an N-terminal thioredoxin-tagged fusion protein in Escherichia coll. The purified recombinant Os4BGlu13 protein (rOs4BGlu13) had an optimum pH of 4.5, for hydrolysis of p-nitrophenyl beta-D-glucopyranoside (pNPGlc), which was the best substrate identified, with a k(cat)/K-m of 637 mM(-1) s(-1). rOs4BGlu13 hydrolyzed helicin best among natural glycosides tested (K-cat/K-m, of 74.4 mM(-1) s(-1)). Os4BGlu13 was previously designated tuberonic acid glucoside (TAG) beta-glucosidase (TAGG), and here the k(cat)/K-m of rOsBGlu13 for TAG was 6.68 mM(-1) s(-1), while that for GA4-GE was 3.63 mM(-1) s(-1) and for salicylic acid glucoside (SAG) is 0.88 mM(-1) s(-1). rOs4BGlu13 also hydrolyzed oligosaccharides, with preference for short beta-(1 -> 3)-linked over beta-(1 -> 4)linked glucooligosaccharides. The enzymatic data suggests that Os4BGlu13 may contribute to TAG, SAG, oligosaccharide and GA4-GE hydrolysis in the rice plant, although helicin or a similar compound may be its primary target. (C) 2015 Elsevier Inc. All rights reserved.