The X-ray structure of the plant like 5-aminolaevulinic acid dehydratase from Chlorobium vibrioforme complexed with the inhibitor laevulinic acid at 2.6 A resolution

Leighton Coates*, Gordon Beaven, Peter T. Erskine, Samuel I. Beale, Yael J. Avissar, Raj Gill, Fiyaz Mohammed, Steve P. Wood, Peter Shoolingin-Jordan, Jon B. Cooper

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

5-Aminolaevulinic acid dehydratase (ALAD), an early enzyme of the tetrapyrrole biosynthesis pathway, catalyses the dimerisation of 5-aminolaevulinic acid to form the pyrrole, porphobilinogen. ALAD from Chlorobium vibrioforme is shown to form a homo-octameric structure with 422 symmetry in which each subunit adopts a TIM-barrel fold with a 30 residue N-terminal arm extension. Pairs of monomers associate with their arms wrapped around each other. Four of these dimers interact principally via their arm regions to form octamers in which each active site is located on the surface. The active site contains two invariant lysine residues (200 and 253), one of which (Lys253) forms a Schiff base link with the bound substrate analogue, laevulinic acid. The carboxyl group of the laevulinic acid forms hydrogen bonds with the side-chains of Ser279 and Tyr318. The structure was examined to determine the location of the putative active-site magnesium ion, however, no evidence for the metal ion was found in the electron density map. This is in agreement with previous kinetic studies that have shown that magnesium stimulates but is not required for activity. A different site close to the active site flap, in which a putative magnesium ion is coordinated by a glutamate carboxyl and five solvent molecules may account for the stimulatory properties of magnesium ions on the enzyme.

Original languageEnglish
Pages (from-to)563-70
Number of pages8
JournalJournal of Molecular Biology
Volume342
Issue number2
Early online date22 Jul 2004
DOIs
Publication statusPublished - 10 Sept 2004

Keywords

  • Allosteric Site
  • Catalytic Domain
  • Chlorobium/chemistry
  • Dimerization
  • Levulinic Acids/chemistry
  • Magnesium/metabolism
  • Porphobilinogen Synthase/antagonists & inhibitors
  • X-Ray Diffraction

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