Elucidation of the Interaction Loci of the Human Pyruvate Dehydrogenase Complex E2·E3BP Core with Pyruvate Dehydrogenase Kinase 1 and Kinase 2 by H/D Exchange Mass Spectrometry and Nuclear Magnetic Resonance

The human pyruvate dehydrogenase complex (PDC) comprises three principal catalytic components for its mission: E1, E2, and E3. The core of the complex is a strong subcomplex between E2 and an E3-binding protein (E3BP). The PDC is subject to regulation at E1 by serine phosphorylation by four kinases (PDK1-4), an inactivation reversed by the action of two phosphatases (PDP1 and -2). We report H/D exchange mass spectrometric (HDX-MS) and nuclear magnetic resonance (NMR) studies in the first attempt to define the interaction loci between PDK1 and PDK2 with the intact E2·E3BP core and their C-terminally truncated proteins. While the three lipoyl domains (L1 and L2 on E2 and L3 on E3BP) lend themselves to NMR studies and determination of interaction maps with PDK1 and PDK2 at the individual residue level, HDX-MS allowed studies of interaction loci on both partners in the complexes, PDKs, and other regions of the E2·E3BP core, as well, at the peptide level. HDX-MS suggested that the intact E2·E3BP core enhances the binding specificity of L2 for PDK2 over PDK1, while NMR studies detected lipoyl domain residues unique to interaction with PDK1 and PDK2. The E2·E3BP core induced more changes on PDKs than any C-terminally truncated protein, with clear evidence of greater plasticity of PDK1 than of PDK2. The effect of L1L2S paralleled HDX-MS results obtained with the intact E2·E3BP core; hence, L1L2S is an excellent candidate with which to define interaction loci with these two PDKs. Surprisingly, L3S' induced moderate interaction with both PDKs according to both methods.