Abstract
The gene encoding the novel amylolytic enzyme designated CoMA was cloned from Corallococcus sp. strain EGB. The deduced amino acid sequence contained a predicted lipoprotein signal peptide (residues 1 to 18) and a conserved glycoside hydrolase family 13 (GH13) module. The amino acid sequence of CoMA exhibits low sequence identity (10 to 19%) with cyclodextrin-hydrolyzing enzymes (GH13_20) and is assigned to GH13_36. The most outstanding feature of CoMA is its ability to catalyze the conversion of maltooligosaccharides (≥G3) and soluble starch to maltose as the sole hydrolysate. Moreover, it can hydrolyze γ-cyclodextrin and starch to maltose and hydrolyze pullulan exclusively to panose with relative activities of 0.2, 1, and 0.14, respectively. CoMA showed both hydrolysis and transglycosylation activities toward α-1,4-glycosidic bonds but not to α-1,6-linkages. Moreover, glucosyl transfer was postulated to be the major transglycosidation reaction for producing a high level of maltose without the attendant production of glucose. These results indicated that CoMA possesses some unusual properties that distinguish it from maltogenic amylases and typical α-amylases. Its physicochemical properties suggested that it has potential for commercial development.IMPORTANCE The α-amylase from Corallococcus sp. EGB, which was classified to the GH13_36 subfamily, can catalyze the conversion of maltooligosaccharides (≥G3) and soluble starch to maltose as the sole hydrolysate. An action mechanism for producing a high level of maltose without the attendant production of glucose has been proposed. Moreover, it also can hydrolyze γ-cyclodextrin and pullulan. Its biochemical characterization suggested that CoMA may be involved the accumulation of maltose in Corallococcus media.