Succinyl-CoA : 3-ketoacid CoA transferase (SCOT): Cloning of the human SCOT gene, tertiary structural modeling of the human SCOT monomer, and characterization of three pathogenic mutations

The activity of succinyl-CoA:3-ketoacid CoA transferase (SCOT; locus symbol OXCT; EC 2.8.3.5) is the main determinant of the ketolytic capacity of tis sues. Hereditary SCOT deficiency causes episodic ketoacidosis. Here we desc ribe the human SCOT gene, which spans more than 100 kb and contains 17 exon s, on chromosome 5p13. We report pathogenic missense mutations in three SCO T-deficient patients designated GS04, 05, and 06, GS04 is a G219E/G324E com pound; GS05 is a V221M homozygote, and GS06 is a G324E homozygote. We const ructed a tertiary structural model of human SCOT by homology modeling based on the known structure of Acidaminococcus fermentans glutaconate CoA trans ferase. The model predicts that V221 and G219 are on the dimerizing surface , whereas G324 is near the active site. SCOT activity was reduced to a comp arable degree in all three patients, but in a transient expression assay in SCOT-deficient fibroblasts, cDNAs containing G219E and G324E produced no d etectable activity, whereas V221M constructs yielded similar to 10% of the control peptide level and detectable specific activity, Interestingly, GS05 had the mildest clinical course reported to date and detectable levels of SCOT protein in fibroblasts. (C) 2000 Academic Press.