3A4A

Crystal structure of isomaltase from Saccharomyces cerevisiae

Summary for 3A4A

• Entry DOI: 10.2210/pdb3a4a/pdb
• Related: 3A47
• Descriptor: Oligo-1,6-glucosidase, alpha-D-glucopyranose, CALCIUM ION, ... (4 entities in total)
• Functional Keywords: (beta/alpha)8-barrel, hydrolase
• Biological source: Saccharomyces cerevisiae (yeast)
• Cellular location: Mitochondrion : P53051
• Total number of polymer chains: 1
• Total formula weight: 68897.57

Authors

Yamamoto, K.,Miyake, H.,Kusunoki, M.,Osaki, S. (deposition date: 2009-07-01, release date: 2010-07-14, Last modification date: 2023-11-01)

Primary citation

Yamamoto, K.,Miyake, H.,Kusunoki, M.,Osaki, S.
Crystal structures of isomaltase from Saccharomyces cerevisiae and in complex with its competitive inhibitor maltose
Febs J., 277:4205-4214, 2010

PubMed Abstract: The structures of isomaltase from Saccharomyces cerevisiae and in complex with maltose were determined at resolutions of 1.30 and 1.60 Å, respectively. Isomaltase contains three domains, namely, A, B, and C. Domain A consists of the (β/α)(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 highest activity towards isomaltose and very little activity towards longer oligosaccharides. This is because the entrance to the active site pocket of isomaltose is severely narrowed by Tyr158, His280, and loop 310-315, and because the isomaltase pocket is shallower than that of other oligo-1,6-glucosidases. These features of the isomaltase active site pocket prevent isomalto-oligosaccharides from binding to the active site effectively.

PubMed: 20812985
DOI: 10.1111/j.1742-4658.2010.07810.x

Experimental method

X-RAY DIFFRACTION (1.6 Å)