Multiple active site histidine protonation states in Acetobacter aceti N5-carboxyaminoimidazole ribonucleotide mutase detected by REDOR NMR.

ABSTRACT: Class I PurE (N5-carboxyaminoimidazole mutase) catalyzes a chemically unique mutase reaction. A working mechanistic hypothesis involves a histidine (His45 in Escherichia coli PurE) functioning as a general acid, but no evidence for multiple protonation states has been obtained. Solution NMR is a peerless tool for this task but has had limited application to enzymes, most of which are larger than its effective molecular size limit. Solid-state NMR is not subject to this limit. REDOR NMR studies of a 151 kDa complex of uniformly 15N-labeled Acetobacter aceti PurE (AaPurE) and the active site ligand [6-13C]citrate probed a single ionization equilibrium associated with the key histidine (AaPurE His59). In the AaPurE complex, the citrate central carboxylate C6 13C peak moves upfield, indicating

SUBMITTER: Schaefer J 

PROVIDER: S-EPMC2793534 | biostudies-literature | 2007 Aug

REPOSITORIES: biostudies-literature