Enantioselective oxidation of galactitol 1-phosphate by galactitol-1-phosphate 5-dehydrogenase fromEscherichia coli

Abstract

Galactitol-1-phosphate 5-dehydrogenase (GPDH) is a polyol dehydrogenase that belongs to the medium-chain dehydrogenase/reductase (MDR) superfamily. It catalyses the Zn(2+)- and NAD(+)-dependent stereoselective dehydrogenation of L-galactitol 1-phosphate to D-tagatose 6-phosphate. Here, three crystal structures of GPDH from Escherichia coli are reported: that of the open state of GPDH with Zn(2+) in the catalytic site and those of the closed state in complex with the polyols Tris and glycerol, respectively. The closed state of GPDH reveals no bound cofactor, which is at variance with the conformational transition of the prototypical mammalian liver alcohol dehydrogenase. The main intersubunit-contacting interface within the GPDH homodimer presents a large internal cavity that probably facilitates the relative movement between the subunits. The substrate analogue glycerol bound within the active site partially mimics the catalytically relevant backbone of galactitol 1-phosphate. The glycerol binding mode reveals, for the first time in the polyol dehydrogenases, a pentacoordinated zinc ion in complex with a polyol and also a strong hydrogen bond between the primary hydroxyl group and the conserved Glu144, an interaction originally proposed more than thirty years ago that supports a catalytic role for this acidic residue.

Dynamic Behavior of Trigger Factor on the Ribosome

“…This compaction was localized below the constriction formed by the ribosomal proteins uL4 and uL22, a region of the tunnel which allows α-helix formation [8][9][10][11]. This feature coincides with α-helical conformation in a recently published GatD crystal structure from E. coli (PDB: 4UEJ residues C92 to C103) [24]. We therefore concluded that the compaction is the result of α-helix formation within this region of the tunnel (see Fig.…”

Functional Characterization of the ycjQRS Gene Cluster from Escherichia coli: A Novel Pathway for the Transformation of d-Gulosides to d-Glucosides

“…YcjQ was purified to homogeneity and found to have a metal content of 0.7 equiv of zinc/enzyme subunit. The sequence similarity network (Figure S3) for YcjQ contains several proteins whose catalytic properties have been determined previously: scyllo -inosose-3-dehydrogenase from Thermotoga maritima , l -galactonate-5-dehydrogenase from Bacteroides vulgatus , galactitol-1-phosphate-5-dehydrogenase from E. coli K-12 MG1655, and sorbitol dehydrogenase from Bacillus subtilis . − However, there are no experimentally verified homologues close to the cluster containing YcjQ. YcjQ was screened for catalytic activity against the library of hexoses (Scheme S1), and the activity was observed only with d -gulose ( 8 ).…”