A case of the Rett syndrome with acute encephalopathy induced during calcium hopantenate treatment

Hereditary and acquired diseases of acyl-coenzyme A metabolism

Coenzyme A (CoA) sequestration, toxicity or redistribution (CASTOR) is predicted to occur in many hereditary and acquired conditions in which the degradation of organic acyl esters of CoA is impaired. The resulting accumulation of CoA esters and reduction of acetyl-CoA and free CoA (CoASH) will then trigger a cascade of reactions leading to clinical disease. Most conditions detected by expanded neonatal screening are CASTOR diseases. We review acyl-CoA metabolism, including CoASH synthesis, transesterification of acyl-CoAs to glycine, glutamate or l-carnitine and hydrolysis of CoA esters. Because acyl-CoAs do not cross biological membranes, their main toxicity is intracellular, primarily within mitochondria. Treatment measures directed towards removal of circulating metabolites do not address this central problem of intracellular acyl-CoA accumulation. Treatments usually involve the restriction of dietary precursors and administration of agents like l-carnitine and glycine, which can accept the transfer of acyl groups from acyl-CoA, liberating CoASH. Many hereditary CASTOR patients are chronically ill, with persistent symptoms and continuously abnormal metabolites in blood and urine despite good compliance with treatment. Conversely, asymptomatic patients are also common in hereditary CASTOR conditions. Future challenges include the understanding of pathophysiologic mechanisms in CASTOR diseases, the discovery of reliable predictors of outcome in individual patients and the establishment of therapeutic trials with sufficient numbers of patients to permit solid therapeutic conclusions.

The Structure of the Pantothenate Kinase·ADP·Pantothenate Ternary Complex Reveals the Relationship between the Binding Sites for Substrate, Allosteric Regulator, and Antimetabolites

Pantothenate kinase catalyzes the first step in the biosynthesis of coenzyme A, the major acyl group carrier in biology. In bacteria, regulation of pantothenate kinase activity is a major factor in controlling intracellular coenzyme A levels, and pantothenate analogs are growth-inhibiting antimetabolites. We have extended the structural information on Escherichia coli pantothenate kinase by determining the structure of the enzyme.ADP. pantothenate ternary complex. Pantothenate binding induces a significant conformational change in amino acids 243-263, which form a "lid" that folds over the open pantothenate binding groove. The positioning of the substrates suggests the reaction proceeds by a concerted mechanism that involves a dissociative transition state, although the negative charge neutralization of the gamma-phosphate by Arg-243, Lys-101, and Mg(2+) coupled with hydrogen bonding of the C1 of pantothenate to Asp-127 suggests different interpretations of the phosphoryl transfer mechanism of pantothenate kinase. N-alkylpantothenamides are substrates for pantothenate kinase. Modeling these antimetabolites into the pantothenate active site predicts that they bind in the same orientation as pantothenate with their alkyl chains interacting with the hydrophobic dome over the pantothenate pocket, which is also accessed by the beta-mercaptoethylamine moiety of the allosteric regulator, coenzyme A. These structural/biochemical studies illustrate the intimate relationship between the substrate, allosteric regulator, and antimetabolite binding sites on pantothenate kinase and provide a framework for studies of its catalysis and feedback regulation.