PDBsum entry 1nwc

Oxidoreductase

PDB id: 1nwc

Contents

Protein chains

356 a.a. *

Waters ×366

* Residue conservation analysis

References listed in PDB file

Key reference

Title

Capture of an intermediate in the catalytic cycle of l-Aspartate-Beta-Semialdehyde dehydrogenase.

Authors

J.Blanco, R.A.Moore, R.E.Viola.

Ref.

Proc Natl Acad Sci U S A, 2003, 100, 12613-12617. [DOI no: 10.1073/pnas.1634958100]

PubMed id

14559965

Abstract

The structural analysis of an enzymatic reaction intermediate affords a unique opportunity to study a catalytic mechanism in extraordinary detail. Here we present the structure of a tetrahedral intermediate in the catalytic cycle of aspartate-beta-semialdehyde dehydrogenase (ASADH) from Haemophilus influenzae at 2.0-A resolution. ASADH is not found in humans, yet its catalytic activity is required for the biosynthesis of essential amino acids in plants and microorganisms. Diaminopimelic acid, also formed by this enzymatic pathway, is an integral component of bacterial cell walls, thus making ASADH an attractive target for the development of new antibiotics. This enzyme is able to capture the substrates aspartate-beta-semialdehyde and phosphate as an active complex that does not complete the catalytic cycle in the absence of NADP. A distinctive binding pocket in which the hemithioacetal oxygen of the bound substrate is stabilized by interaction with a backbone amide group dictates the R stereochemistry of the tetrahedral intermediate. This pocket, reminiscent of the oxyanion hole found in serine proteases, is completed through hydrogen bonding to the bound phosphate substrate.

Figure 4.
Fig. 4. Schematic representation of the ASADH active site with a bound hemithioacetal reaction intermediate. Interactions between ASA and phosphate and key active site residues are shown.

Figure 6.
Fig. 6. Proposed mechanism for the catalytic cycle of ASADH shown in reverse biological direction. (A) Tetrahedral intermediate derived from reaction with ASA. (B) Proposed acyl intermediate with trigonal planar geometry. (C) Second tetrahedral intermediate with covalently bound aspartyl phosphate.