The X-ray structure of yeast 5-aminolaevulinic acid dehydratase complexed with substrate and three inhibitors

The structures of 5-aminolaevulinic acid dehydratase (ALAD) complexed with substrate (5-aminolaevulinic acid) and three inhibitors: laevulinic acid, s uccinylacetone and 4-keto-5-aminolaevulinic acid, have been solved at high resolution. The ligands all bind by forming a covalent link with Lys263 at the active site. The structures define the interactions made by one of the two substrate moieties that bind to the enzyme during catalysis. All of the inhibitors induce a significant ordering of the flap covering the active s ite. Succinylacetone appears to be unique by inducing a number of conformat ional changes in loops covering the active site, which may be important for understanding the co-operative properties of ALAD enzymes. Succinylacetone is produced in large amounts by patients suffering from the hereditary dis ease type I tyrosinaemia and its potent inhibition of ALAD also has implica tions for the pathology of this disease. The most intriguing result is that obtained with 4-keto-5-aminohexanoic acid, which seems to form a stable ca rbinolamine intermediate with Lys263. It appears that we have defined the s tructure of an intermediate of Schiff base formation that the substrate for ms upon binding to the P-site of the enzyme. (C) 2001 Academic Press.