| Abstract
| - 3-Keto-l-gulonate 6-phosphate decarboxylase (KGPDC) and d-arabino-hex-3-ulose 6-phosphatesynthase (HPS), members of the orotidine 5‘-monophosphate decarboxylase (OMPDC) suprafamily, catalyzereactions that involve the formation of Mg2+-ion stabilized 1,2-enediolate intermediates. The active sitesof KGPDC and HPS share several conserved residues, including the presumed ligands for the Mg2+ anda catalytic histidine residue that has been implicated in protonation of the intermediate in the KGPDC-catalyzed reaction. As reported in the previous manuscript, both enzymes are naturally promiscuous, withKGPDC from Escherichia coli catalyzing a low level of the HPS reaction and the HPS from Methylomonasaminofaciens catalyzing a significant level of the KGPDC reaction. Interestingly, the promiscuous HPSreaction catalyzed by KGPDC can be significantly enhanced by replacing no more than four active siteresidues from KGPDC reaction with residues from HPS. In this manuscript, we report structural studiesof wild-type and mutant KDGPC's that provide a structural explanation for both the natural promiscuityfor the HPS reaction and the enhanced HPS activity and diminished KGPDC activity catalyzed by activesite mutants.
|
