Variation in the organization and subunit composition of the mammalian pyruvate dehydrogenase complex E2/E3BP core assembly

Vijayakrishnan, Swetha, Callow, Philip, Nutley, Margaret A., McGow, Donna P., Gilbert, David, Kropholler, Peter, Cooper, Alan, Byron, Olwyn and Lindsay, J. Gordon (2011) Variation in the organization and subunit composition of the mammalian pyruvate dehydrogenase complex E2/E3BP core assembly. Biochemical Journal, 437 (3), 565-574. (doi:10.1042/BJ20101784). (PMID:21627584)

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.

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Contributors

Author: Peter Kropholler

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