title: Calcium-insensitive splice variants of mammalian E1 subunit of 2-oxoglutarate dehydrogenase complex with tissue-specific patterns of expression.
abstract: The 2-oxoglutarate dehydrogenase (OGDH) complex is an important control point in vertebrate mitochondrial oxidative metabolism, including in the citrate cycle and catabolism of alternative fuels including glutamine. It is subject to allosteric regulation by NADH and the ATP/ADP ratio, and by Ca(2+) through binding to the E1 subunit. The latter involves a unique Ca(2+)-binding site which includes D(114)ADLD (site 1). Here, we describe three splice variants of E1 in which either the exon expressing this site is replaced with another exon (loss of site 1, LS1) or an additional exon is expressed leading to the insertion of 15 amino acids just downstream of site 1 (Insert), or both changes occur together (LS1/Insert). We show that all three variants are essentially Ca(2+)-insensitive. Comparison of massive parallel sequence (RNA-Seq) databases demonstrates predominant expression of the Ca(2+)-sensitive archetype form in heart and skeletal muscle, but substantial expression of the Ca(2+)-insensitive variants in brain, pancreatic islets and other tissues. Detailed proteomic and activity studies comparing OGDH complexes from rat heart and brain confirmed the substantial difference in expression between these tissues. The evolution of OGDH variants was explored using bioinformatics, and this indicated that Ca(2+)-sensitivity arose with the emergence of chordates. In all species examined, this was associated with the co-emergence of Ca(2+)-insensitive variants suggesting a retained requirement for the latter in some settings. Tissue-specific expression of OGDH splice variants may thus provide a mechanism that tunes the control of the enzyme to the specialized metabolic and signalling needs of individual cell types.
authors.affiliation: School of Biochemistry, Biomedical Sciences Building, University Walk, University of Bristol, Bristol BS8 1TD, U.K. r.denton@bristol.ac.uk.
authors.forename: Richard M
authors.initials: RM
authors.lastname: Denton
authors.affiliation: Section of Cell Biology and Functional Genomics, Department of Medicine, ICTEM Building, Hammersmith Campus, Imperial College, du Cane Road, London W12 ONN, U.K.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Pullen
authors.affiliation: School of Biochemistry, Biomedical Sciences Building, University Walk, University of Bristol, Bristol BS8 1TD, U.K.
authors.forename: Craig T
authors.initials: CT
authors.lastname: Armstrong
authors.affiliation: School of Biochemistry, Biomedical Sciences Building, University Walk, University of Bristol, Bristol BS8 1TD, U.K.
authors.forename: Kate J
authors.initials: KJ
authors.lastname: Heesom
authors.affiliation: Section of Cell Biology and Functional Genomics, Department of Medicine, ICTEM Building, Hammersmith Campus, Imperial College, du Cane Road, London W12 ONN, U.K.
authors.forename: Guy A
authors.initials: GA
authors.lastname: Rutter
mesh_terms: D017398:Alternative Splicing / Q000502:physiology*; D000818:Animals; D002262:Carboxy-Lyases / Q000096:biosynthesis* / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D006801:Humans; D007655:Ketoglutarate Dehydrogenase Complex / Q000096:biosynthesis* / Q000235:genetics; D008297:Male; D009928:Organ Specificity / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar
chemical_list: D007655:Ketoglutarate Dehydrogenase Complex; D002262:Carboxy-Lyases; C021474:2-oxoglutarate decarboxylase
keywords: RNA-Seq; allosteric regulation; brain; citrate cycle; heart; proteomic analysis