title: Expression and Biochemical Characterization of a Thermostable Branching Enzyme from Geobacillus thermoglucosidans.
abstract: The branching enzyme (EC 2.4.1.18) catalyzes the formation of α-1,6 branch points in starch. In this study, the Geobacillus thermoglucosidans gene-encoding branching enzyme was expressed in Escherichia coli BL21 (DE3) and the protein was isolated and characterized. G. thermoglucosidans branching enzyme is a thermostable enzyme with an optimal reaction temperature of nearly 60°C and a half-life at 65°C of approximately 1.1 h. The activity of the recombinant enzyme is optimal at pH 7.5, with broad stability between pH 5.5 and 9.0. Its thermostability, relatively broad pH stability and optimal temperature near the temperature at which starch begins to gelatinize may make it easy to use in industrial production. Furthermore, the enzyme is activated by Mg2+, Ba2+, K+ and Na+ in a concentration-dependent manner and dramatically inhibited by Ni2+ and Co2+. Its substrate dependence, using amylopectin as the substrate, could be adequately fitted using the Michaelis-Menten equation, yielding a Km of 0.99 mg/ml. High-performance anion exchange chromatography results showed that the chain length distribution of branching enzyme-treated waxy corn starch is indistinguishable from that of the branching enzyme-treated common corn starch. This enzyme may therefore be a promising tool for the enzymatic modification of starch.
authors.affiliation: State Key Laboratory of Food Science and Technology, Jiangnan University, Wuxi, China.
authors.forename: Xiaofeng
authors.initials: X
authors.lastname: Ban
authors.forename: Caiming
authors.initials: C
authors.lastname: Li
authors.forename: Zhengbiao
authors.initials: Z
authors.lastname: Gu
authors.forename: Chunhui
authors.initials: C
authors.lastname: Bao
authors.forename: Yijing
authors.initials: Y
authors.lastname: Qiu
authors.forename: Yan
authors.initials: Y
authors.lastname: Hong
authors.forename: Li
authors.initials: L
authors.lastname: Cheng
authors.forename: Zhaofeng
authors.initials: Z
authors.lastname: Li
mesh_terms: D015061:1,4-alpha-Glucan Branching Enzyme / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism*; D003001:Cloning, Molecular; D020536:Enzyme Activators; D004791:Enzyme Inhibitors; D004795:Enzyme Stability; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D015870:Gene Expression; D056506:Geobacillus / Q000201:enzymology* / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D007477:Ions; D007700:Kinetics; D008670:Metals; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D013213:Starch / Q000378:metabolism*; D013696:Temperature; D003313:Zea mays / Q000737:chemistry
chemical_list: D020536:Enzyme Activators; D004791:Enzyme Inhibitors; D007477:Ions; D008670:Metals; D011994:Recombinant Proteins; D013213:Starch; D015061:1,4-alpha-Glucan Branching Enzyme