Identification And Phylogenetic Characterization Of A New A-Amylase Enzymes From Marine Microorganisms And A Functional Analysis Of The C-Terminal Module

The a-amylases are very important enzymes in industy,they are widely applied in Starch processing,Ethanol producing,food manufacturing and other industrial field.the study of the a-amylases are very active nowdays.In this study,A gene encoding a starch hydrolyzing enzyme was isolated from a marine metagenomic library and over expressed in E.coli.The enzyme,designated AmyP,shows no similarity to sequences of known ?-amylases,although a catalytic domain correlated with the a-amylase superfamily was identified.Based on biochemical analysis,the protein was clearly defined as a saccharifying-type a-amylase.Sequence comparison indicated that AmyP was related to four putative glycosidases previously identified only in bacterial genome sequences.They were all from marine bacteria and formed a new subfamily of glycoside hydrolase GH13.Moreover,this subfamily GH13-37 was closely related to the probable genuine bacterial a-amylases(GH13-19).The results suggested that GH13-37 may be an independent clade of ancestral marine bacterial.The ?-amylases AmyP has a starch binding domain(SBD),it is a functional domain responsible for binding to starch gran?les,it is composed of 148 amino acids.The SBD does not have catalytic activity,Protein binding assays showed this SBD has a function of adsorption and increased capacity of hydrolysis of starch gran?les.