title: Variation in the organization and subunit composition of the mammalian pyruvate dehydrogenase complex E2/E3BP core assembly.
abstract: Crucial to glucose homoeostasis in humans, the hPDC (human pyruvate dehydrogenase complex) is a massive molecular machine comprising multiple copies of three distinct enzymes (E1-E3) and an accessory subunit, E3BP (E3-binding protein). Its icosahedral E2/E3BP 60-meric 'core' provides the central structural and mechanistic framework ensuring favourable E1 and E3 positioning and enzyme co-operativity. Current core models indicate either a 48E2+12E3BP or a 40E2+20E3BP subunit composition. In the present study, we demonstrate clear differences in subunit content and organization between the recombinant hPDC core (rhPDC; 40E2+20E3BP), generated under defined conditions where E3BP is produced in excess, and its native bovine (48E2+12E3BP) counterpart. The results of the present study provide a rational basis for resolving apparent differences between previous models, both obtained using rhE2/E3BP core assemblies where no account was taken of relative E2 and E3BP expression levels. Mathematical modelling predicts that an 'average' 48E2+12E3BP core arrangement allows maximum flexibility in assembly, while providing the appropriate balance of bound E1 and E3 enzymes for optimal catalytic efficiency and regulatory fine-tuning. We also show that the rhE2/E3BP and bovine E2/E3BP cores bind E3s with a 2:1 stoichiometry, and propose that mammalian PDC comprises a heterogeneous population of assemblies incorporating a network of E3 (and possibly E1) cross-bridges above the core surface.
authors.affiliation: School of Life Sciences, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, UK.
authors.forename: Swetha
authors.initials: S
authors.lastname: Vijayakrishnan
authors.forename: Philip
authors.initials: P
authors.lastname: Callow
authors.forename: Margaret A
authors.initials: MA
authors.lastname: Nutley
authors.forename: Donna P
authors.initials: DP
authors.lastname: McGow
authors.forename: David
authors.initials: D
authors.lastname: Gilbert
authors.forename: Peter
authors.initials: P
authors.lastname: Kropholler
authors.forename: Alan
authors.initials: A
authors.lastname: Cooper
authors.forename: Olwyn
authors.initials: O
authors.lastname: Byron
authors.forename: J Gordon
authors.initials: JG
authors.lastname: Lindsay
mesh_terms: D000818:Animals; D002417:Cattle; D051047:Dihydrolipoyllysine-Residue Acetyltransferase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli; D008956:Models, Chemical; D011485:Protein Binding; D011487:Protein Conformation; D011994:Recombinant Proteins
chemical_list: D011994:Recombinant Proteins; D051047:Dihydrolipoyllysine-Residue Acetyltransferase