title: X-ray structure of 5-aminolaevulinate dehydratase, a hybrid aldolase.
abstract: 5-Aminolaevulinate dehydratase (ALAD) is a homo-octameric metallo-enzyme that catalyses the formation of porphobilinogen from 5-aminolaevulinic acid. The structure of the yeast enzyme has been solved to 2.3 A resolution, revealing that each subunit adopts a TIM barrel fold with a 39 residue N-terminal arm. Pairs of monomers wrap their arms around each other to form compact dimers and these associate to form a 422 symmetric octamer. All eight active sites are on the surface of the octamer and possess two lysine residues (210 and 263), one of which, Lys 263, forms a Schiff base link to the substrate. The two lysine side chains are close to two zinc binding sites one of which is formed by three cysteine residues (133, 135 and 143) while the other involves Cys 234 and His 142. ALAD has features at its active site that are common to both metallo- and Schiff base-aldolases and therefore represents an intriguing combination of both classes of enzyme. Lead ions, which inhibit ALAD potently, replace the zinc bound to the enzyme's unique triple-cysteine site.
authors.affiliation: School of Biological Sciences, University of Southampton, UK.
authors.forename: P T
authors.initials: PT
authors.lastname: Erskine
authors.forename: N
authors.initials: N
authors.lastname: Senior
authors.forename: S
authors.initials: S
authors.lastname: Awan
authors.forename: R
authors.initials: R
authors.lastname: Lambert
authors.forename: G
authors.initials: G
authors.lastname: Lewis
authors.forename: I J
authors.initials: IJ
authors.lastname: Tickle
authors.forename: M
authors.initials: M
authors.lastname: Sarwar
authors.forename: P
authors.initials: P
authors.lastname: Spencer
authors.forename: P
authors.initials: P
authors.lastname: Thomas
authors.forename: M J
authors.initials: MJ
authors.lastname: Warren
authors.forename: P M
authors.initials: PM
authors.lastname: Shoolingin-Jordan
authors.forename: S P
authors.initials: SP
authors.lastname: Wood
authors.forename: J B
authors.initials: JB
authors.lastname: Cooper
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D018360:Crystallography, X-Ray; D019281:Dimerization; D005634:Fructose-Bisphosphate Aldolase / Q000737:chemistry; D006801:Humans; D008239:Lysine / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D000623:Porphobilinogen Synthase / Q000737:chemistry* / Q000235:genetics; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics; D017386:Sequence Homology, Amino Acid
chemical_list: D005634:Fructose-Bisphosphate Aldolase; D000623:Porphobilinogen Synthase; D008239:Lysine