|2vd6, resolution 2.00Å ()|
|Ligands:||, , , ,|
Human adenylosuccinate lyase in complex with its substrate N6-(1,2- Dicarboxyethyl)-AMP, and its products AMP and fumarate.
Adenylosuccinate lyase (ASL) catalyzes two beta-elimination reactions in purine biosynthesis, leading to the question of whether the two substrates occupy the same or different active sites. Kinetic studies of Bacillus subtilis and human ASL with a new substrate analog, adenosine phosphonobutyric acid, 2'(3'), 5'-diphosphate (APBADP), show that it acts as a competitive inhibitor with respect to either substrate (K(I) approximately 0.1 microM), indicating that the two substrates occupy the same active site. Binding studies show that both the B. subtilis and human ASLs bind up to 4 mol of APBADP per mole of enzyme tetramer and that both enzymes exhibit cooperativity: negative for B. subtilis ASL and positive for human ASL. Mutant B. subtilis ASLs, with replacements for residues previously identified as critical for catalysis, bind the substrate analog similarly to wild-type ASL. Two serines in a flexible loop of ASL have been proposed to play roles in catalysis because they are close to the substrate in the crystal structure of Escherichia coli ASL. We have now mutated the corresponding serines to alanines in B. subtilis and human ASL to evaluate their involvement in enzyme function. Kinetic data reveal that human Ser(289) and B. subtilis Ser(262) and Ser(263) are essential for catalysis, while the ability of these Ser mutants to bind APBADP suggests that they do not contribute to substrate affinity. Although these serines are not visible in the crystal structure of human adenylosuccinate lyase complexed with substrate or products (PDB #2VD6), they may be interacting with the active sites.
Effect of a new non-cleavable substrate analog on wild-type and serine mutants in the signature sequence of adenylosuccinate lyase of Bacillus subtilis and Homo sapiens., Sivendran S, Colman RF, Protein Sci. 2008 Jul;17(7):1162-74. Epub 2008 May 9. PMID:018469177
From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.
[PUR8_HUMAN] Defects in ADSL are the cause of adenylosuccinase deficiency (ADSL deficiency) [MIM:103050]. ADSL deficiency is an autosomal recessive disorder characterized by the accumulation in the body fluids of succinylaminoimidazole-carboxamide riboside (SAICA-riboside) and succinyladenosine (S-Ado). Most children display marked psychomotor delay, often accompanied by epilepsy or autistic features, or both, although some patients may be less profoundly retarded. Occasionally, growth retardation and muscular wasting are also present.