Streptomyces ST66 Amylomaltase Gene Cloning and Expression and Production of Cycloamylose

The amylomaltase gene of the Streptomyces ST66 was cloned. The open reading frame of this gene consisted of 2,136 nucleotides and encoded a polypeptide that was711 amino acids. The amylomaltase gene was overexpressed in E. coli. The detailed action profile of crude enzyme from E.coli Top 10F´/pTrc-CKS- MalQ on amylose was analyzed and tested whether this crude enzyme could catalyze cyclization of amylose. The mixture solution that was treated by crude enzyme resulted in a rapid decrease of absorbance of iodine-amylose complex and the accumulation of a product that was resistant to an exo-amylase (glucoamylase) but was degraded by an endo-type alpha-amylase to glucose and maltose. These results indicated that the enzyme acted on amylose, it catalyzed an intramolecular transglycosylation (cyclization) reaction which produced cyclic a- 1,4-glucan (cycloamylose), like potato D-enzyme.