PDBsum entry 2hg2

Oxidoreductase

PDB id: 2hg2

Contents

Protein chain

477 a.a.

Ligands

SO4 ×2

Waters ×109

References listed in PDB file

Key reference

Title

Crystal structure of lactaldehyde dehydrogenase from escherichia coli and inferences regarding substrate and cofactor specificity.

Authors

L.Di costanzo, G.A.Gomez, D.W.Christianson.

Ref.

J Mol Biol, 2007, 366, 481-493. [DOI no: 10.1016/j.jmb.2006.11.023]

PubMed id

17173928

Abstract

Aldehyde dehydrogenases catalyze the oxidation of aldehyde substrates to the corresponding carboxylic acids. Lactaldehyde dehydrogenase from Escherichia coli (aldA gene product, P25553) is an NAD(+)-dependent enzyme implicated in the metabolism of l-fucose and l-rhamnose. During the heterologous expression and purification of taxadiene synthase from the Pacific yew, lactaldehyde dehydrogenase from E. coli was identified as a minor (</=5%) side-product subsequent to its unexpected crystallization. Accordingly, we now report the serendipitous crystal structure determination of unliganded lactaldehyde dehydrogenase from E. coli determined by the technique of multiple isomorphous replacement using anomalous scattering at 2.2 A resolution. Additionally, we report the crystal structure of the ternary enzyme complex with products lactate and NADH at 2.1 A resolution, and the crystal structure of the enzyme complex with NADPH at 2.7 A resolution. The structure of the ternary complex reveals that the nicotinamide ring of the cofactor is disordered between two conformations: one with the ring positioned in the active site in the so-called hydrolysis conformation, and another with the ring extended out of the active site into the solvent region, designated the out conformation. This represents the first crystal structure of an aldehyde dehydrogenase-product complex. The active site pocket in which lactate binds is more constricted than that of medium-chain dehydrogenases such as the YdcW gene product of E. coli. The structure of the binary complex with NADPH reveals the first view of the structural basis of specificity for NADH: the negatively charged carboxylate group of E179 destabilizes the binding of the 2'-phosphate group of NADPH sterically and electrostatically, thereby accounting for the lack of enzyme activity with this cofactor.

Figure 1.
Figure 1. Pathways of l-fucose and l-rhamnose metabolism in E. coli. Lactaldehyde dehydrogenase generates l-lactate, which is converted to pyruvate for entry into the central metabolic processes of the cell. Figure 1. Pathways of l-fucose and l-rhamnose metabolism in E. coli. Lactaldehyde dehydrogenase generates l-lactate, which is converted to pyruvate for entry into the central metabolic processes of the cell.

Figure 2.
Figure 2. The NAD^+-dependent oxidation of lactaldehyde to lactate catalyzed by lactaldehyde dehydrogenase. Figure 2. The NAD^+-dependent oxidation of lactaldehyde to lactate catalyzed by lactaldehyde dehydrogenase.

The above figures are reprinted from an Open Access publication published by Elsevier: J Mol Biol (2007, 366, 481-493) copyright 2007.