tailieunhanh - Báo cáo khoa học: Crystal structures of isomaltase from Saccharomyces cerevisiae and in complex with its competitive inhibitor maltose

The structures of isomaltase fromSaccharomyces cerevisiaeand in complex with maltose were determined at resolutions of and A˚ , respec-tively. Isomaltase contains three domains, namely, A, B, and C. Domain A consists of the (b⁄a)8 -barrel common to glycoside hydrolase family 13. However, the folding of domain C is rarely seen in other glycoside hydro-lase family 13 enzymes. | ỊFEBS Journal Crystal structures of isomaltase from Saccharomyces cerevisiae and in complex with its competitive inhibitor maltose Keizo Yamamoto1 Hideo Miyake2 Masami Kusunoki3 and Shigeyoshi Osaki1 1 Schoolof Medicine Nara MedicalUniversity Japan 2 Graduate Schoolof Bioresources Mie University Japan 3 Faculty of Engineering University of Yamanashi Japan Keywords crystal structure glycoside hydrolase family 13 isomaltase substrate binding substrate specificity Correspondence K. Yamamoto Schoolof Medicine Nara MedicalUniversity 840 Shijo Kashihara Nara 634-8521 Japan Fax 81 744 29 8810 Tel 81 744 29 8810 E-mail kama@ Database Structuraldata are available in the Protein Data Bank under the accession numbers 3AJ7 and 3A4A Received 2 June 2010 revised 27 July 2010 accepted 5 August 2010 doi The structures of isomaltase from Saccharomyces cerevisiae and in complex with maltose were determined at resolutions of and A respectively. Isomaltase contains three domains namely A B and C. Domain A consists of the p a 8-barrel common to glycoside hydrolase family 13. However the folding of domain C is rarely seen in other glycoside hydrolase family 13 enzymes. An electron density corresponding to a nonreducing end glucose residue was observed in the active site of isomaltase in complex with maltose however only incomplete density was observed for the reducing end. The active site pocket contains two water chains. One water chain is a water path from the bottom of the pocket to the surface of the protein and may act as a water drain during substrate binding. The other water chain which consists of six water molecules is located near the catalytic residues Glu277 and Asp352. These water molecules may act as a reservoir that provides water for subsequent hydrolytic events. The best substrate for oligo-1 6-glucosidase is isomaltotriose other longer-chain oligosaccharides are also good substrates. However isomaltase shows the