Download MendeleyIsomaltulose synthase (PalI) of Klebsiella sp. LX3. Crystal structure and implication of mechanism
Zhang, D., Li, N., Lok, S.M., Zhang, L.-H., Swaminathan, K.(2003) J Biol Chem 278: 35428-35434
- PubMed: 12819210
- DOI: https://doi.org/10.1074/jbc.M302616200
- Primary Citation of Related Structures:
1M53 - PubMed Abstract:
Isomaltulose synthase from Klebsiella sp. LX3 (PalI, EC 5.4.99.11) catalyzes the isomerization of sucrose to produce isomaltulose (alpha-D-glucosylpyranosyl-1,6-D-fructofuranose) and trehalulose (alpha-D-glucosylpyranosyl-1,1-d-fructofuranose). The PalI structure, solved at 2.2-A resolution with an R-factor of 19.4% and Rfree of 24.2%, consists of three domains: an N-terminal catalytic (beta/alpha)8 domain, a subdomain between N beta 3 and N alpha 3, and a C-terminal domain having seven beta-strands. The active site architecture of PalI is identical to that of other glycoside hydrolase family 13 members, suggesting a similar mechanism in substrate binding and hydrolysis. However, a unique RLDRD motif in the proximity of the active site has been identified and shown biochemically to be responsible for sucrose isomerization. A two-step reaction mechanism for hydrolysis and isomerization, which occurs in the same pocket is proposed based on both the structural and biochemical data. Selected C-terminal truncations have been shown to reduce and even abolish the enzyme activity, consistent with the predicted role of the C-terminal residues in the maintenance of enzyme conformation and active site topology.
Organizational Affiliation:
Department of Pathology, National University of Singapore, 5 Lower Kent Ridge Road, Singapore 119074.
