earticle

영어

Recently, some amylolytic enzymes, designated as glycoside hydrolase family 57 ( GH5 7), are newly assigned as second a -amylase family. The heterothermophilic archaea, Thermococcales, efficiently utilizes the carbohydrates using two main GH57 enzymes, 4-a -glucanotransferase (GTase) and maltose-forming amylase (MAase), which existed in all of reported genomes of the genus Thermococcus and Pyrococcus (1). GTase is specific for a -1,4-glucan with high transferase activity, while MAase is new type amylase, exhibiting unique dual hydrolysis activity toward a -1,4- and a -1,6-glycosidic linkages and only recognizes maltose in exo-type manner (2). The crystal structure of MAase at a resolution of L8 A showed that both enzymes shared similar substrate binding sites based on GH57 core structure ( 13/ah barrel-fold despite of their distinct specificity ( 3). Structural features further demonstrate that both enzymes have an aromatic amino acid residue which is located on the entrance of substrate binding site at + 1 to + 2 in same manner, From the mutagenesis analysis, we revealed that they have distinct role in substrate binding. Aromatic ammo acid residue of GTase can accommodate the substrates at acceptor binding region, while that of MAase can control the binding of substrates linked by a -1,4- or a -1,6-glycosidic bond and limit the length of substrates.