The action mode of Thermus aquaticus YT-1 4-α-glucanotransferase and its chimeric enzymes introduced with starch-binding domain on amylose and amylopectin

A thermostable 4-α-glucanotransferase (TAαGT) gene isolated from Thermus aquaticus YT-1 had an open reading frame of 1503 nucleotides, which encoded 500 amino acid residues for a 57,969 dalton protein. The maximum activity of the TAαGT was observed at pH 7.5 and 70 °C. The enzyme catalyzed intermolecular transglycosylation of maltooligosaccharides (disproportionation) to produce linear α-1,4-glucans of various sizes. The starch-binding domains (SBD) of Bacillus stearothermophilus ET1 CGTase (E and DE) were introduced into the C-terminus of TAαGT to enhance the starch utilizing activity. The chimeric enzymes, TAαGT-E and TAαGT-DE, showed no difference in temperature optimum, transglycosylation activity, and amylolytic degradation pattern compared to TAαGT wild-type. However, TAαGT-DE exhibited the highest molar specific activity toward amylose. TAαGT-DE modified amylopectin molecules by its disproportionating activities to produce modified amylopectin clusters (Mw 105–106). Also, it demonstrated the ability to produce cyclo-amyloses with DP of 19 through 35 from amylose molecules.