title: X-linked sideroblastic anemia due to carboxyl-terminal ALAS2 mutations that cause loss of binding to the β-subunit of succinyl-CoA synthetase (SUCLA2).
abstract: Mutations in the erythroid-specific aminolevulinic acid synthase gene (ALAS2) cause X-linked sideroblastic anemia (XLSA) by reducing mitochondrial enzymatic activity. Surprisingly, a patient with the classic XLSA phenotype had a novel exon 11 mutation encoding a recombinant enzyme (p.Met567Val) with normal activity, kinetics, and stability. Similarly, both an expressed adjacent XLSA mutation, p.Ser568Gly, and a mutation (p.Phe557Ter) lacking the 31 carboxyl-terminal residues also had normal or enhanced activity, kinetics, and stability. Because ALAS2 binds to the β subunit of succinyl-CoA synthetase (SUCLA2), the mutant proteins were tested for their ability to bind to this protein. Wild type ALAS2 bound strongly to a SUCLA2 affinity column, but the adjacent XLSA mutant enzymes and the truncated mutant did not bind. In contrast, vitamin B6-responsive XLSA mutations p.Arg452Cys and p.Arg452His, with normal in vitro enzyme activity and stability, did not interfere with binding to SUCLA2 but instead had loss of positive cooperativity for succinyl-CoA binding, an increased K(m) for succinyl-CoA, and reduced vitamin B6 affinity. Consistent with the association of SUCLA2 binding with in vivo ALAS2 activity, the p.Met567GlufsX2 mutant protein that causes X-linked protoporphyria bound strongly to SUCLA2, highlighting the probable role of an ALAS2-succinyl-CoA synthetase complex in the regulation of erythroid heme biosynthesis.
authors: Department of Genetics and Genomic Sciences, Mount Sinai School of Medicine, New York, New York 10029, USA.
authors: David F
authors: DF
authors: Bishop
authors: Vassili
authors: V
authors: Tchaikovskii
authors: A Victor
authors: AV
authors: Hoffbrand
authors: Marie E
authors: ME
authors: Fraser
authors: Steven
authors: S
authors: Margolis
mesh_terms: D000624:5-Aminolevulinate Synthetase / Q000235:genetics / Q000378:metabolism*; D000328:Adult; D019943:Amino Acid Substitution; D000756:Anemia, Sideroblastic / Q000201:enzymology / Q000235:genetics; D004795:Enzyme Stability / Q000235:genetics; D040181:Genetic Diseases, X-Linked / Q000201:enzymology / Q000235:genetics; D006418:Heme / Q000096:biosynthesis / Q000235:genetics; D006801:Humans; D008297:Male; D020125:Mutation, Missense; D011485:Protein Binding; D046351:Protoporphyria, Erythropoietic / Q000201:enzymology / Q000235:genetics; D013389:Succinate-CoA Ligases / Q000235:genetics / Q000378:metabolism*; D025101:Vitamin B 6 / Q000235:genetics / Q000378:metabolism
chemical_list: D006418:Heme; D025101:Vitamin B 6; D000624:5-Aminolevulinate Synthetase; C480079:ALAS2 protein, human; D013389:Succinate-CoA Ligases; C518788:SUCLA2 protein, human