title: A mutant alpha-amylase with only part of the catalytic domain and its structural implication.
abstract: A truncated mutant alpha-amylase, Xa-S2, was obtained from Xanthomonas campestris wild type alpha-amylases (Xa-WT) through random mutagenesis that contained 167 amino acid residues (approx 65% shorter than that of Xa-WT). Secondary structure prediction implied that Xa-S2, would be unable to form the whole (beta/alpha)(8)-barrel catalytic domain and did not have the three conserved catalytic residues of wild type alpha-amylase, but it still displays the starch-hydrolyzing activity. Xa-S2 was prepared, characterized and compared to the recombinant wild-type enzymes. The K (m) for starch was 32 mg/ml; activity was optimal at pH 6.2 and 30 degrees C. In contrast, the K (m) for starch of Xa-WT was 8 mg/ml and optimal enzyme activity was at pH 6.0-6.2 and 45-50 degrees C. Our results suggested that Xa-S2 is a new amylase with a minimal catalytic domain for hydrolyzing substrates with of alpha-1,4-glucosidic bonds.
authors.affiliation: China-UK HUST-RRes Genetic Engineering and Genomics Joint Laboratory, Huazhong University of Science and Technology, Wuhan, Hubei, China.
authors.forename: T
authors.initials: T
authors.lastname: Ke
authors.forename: X D
authors.initials: XD
authors.lastname: Ma
authors.forename: P H
authors.initials: PH
authors.lastname: Mao
authors.forename: X
authors.initials: X
authors.lastname: Jin
authors.forename: S J
authors.initials: SJ
authors.lastname: Chen
authors.forename: Y
authors.initials: Y
authors.lastname: Li
authors.forename: L X
authors.initials: LX
authors.lastname: Ma
authors.forename: G Y
authors.initials: GY
authors.lastname: He
mesh_terms: D000595:Amino Acid Sequence; D002384:Catalysis; D004789:Enzyme Activation; D004795:Enzyme Stability; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D017434:Protein Structure, Tertiary; D013329:Structure-Activity Relationship; D016959:Xanthomonas campestris / Q000201:enzymology* / Q000235:genetics; D000516:alpha-Amylases / Q000737:chemistry* / Q000235:genetics*
chemical_list: D000516:alpha-Amylases