Enzymatic properties of an efficient glucan branching enzyme and its potential application in starch modification.

Affiliation

Chengyao X(1), Yan Q(1), Chaonan D(1), Xiaopei C(1), Yanxin W(1), Ding L(2), Xianfeng Y(1), Jian H(3), Yan H(1), Zhongli C(1), Zhoukun L(4).
Author information:
(1)Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture, College of Life Science, Nanjing Agricultural University, Nanjing, 210095, PR China.
(2)Institute of Veterinary Immunology &Engineering, Jiangsu Academy of Agricultural Sciences, Nanjing, 210014, PR China.
(3)College of Agriculture, Xinjiang Agricultural University, XinJiang, 830052, China.
(4)Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture, College of Life Science, Nanjing Agricultural University, Nanjing, 210095, PR China. Electronic address: [Email]

Abstract

Glucan branching enzymes (GBEs, EC 2.4.1.18) catalyze the formation of α-1,6-linked branch in starch, which is important for the starch modification with prospective properties. In this study, the aqGBE gene encoding an efficient glucan branching enzyme was cloned from Aquabacterium sp. strain A7-Y and successfully expressed in Escherichia coli BL21 (DE3). The specific activity of the purified recombinant enzyme rAqGBE was 2850 U/mg with potato starch as the optimal substrate, and the Km and Vmax values of rAqGBE were 1.18 mg/mL and 588.2 μmol/min/mg, respectively. Enzymological characterization showed that rAqGBE exhibits its optimal activity under the condition of 40 °C and pH 7.0, respectively, which is independent of calcium ions. Otherwise, rAqGBE-treated potato starch showed different chain length distribution compared with control, the numbers of short chains (degree of polymerization, DP < 7) and long chains (DP > 25) increased from 4.5% to 9.6% and 6.1%-15.7% after enzymatic treatment, respectively. In starch anti-ageing assay, with minimum usage of 0.8 mg rAqGBE per g starch, the rAqGBE-treated potato starch exhibited reduced retrogradation properties. Our results indicate that the branching enzyme AqGBE may therefore be a promising tool for the enzymatic modification of starch.