title: Efficient coupling of catalysis and dynamics in the E1 component of Escherichia coli pyruvate dehydrogenase multienzyme complex.
abstract: Protein motions are ubiquitous and are intrinsically coupled to catalysis. Their specific roles, however, remain largely elusive. Dynamic loops at the active center of the E1 component of Escherichia coli pyruvate dehydrogenase multienzyme complex are essential for several catalytic functions starting from a predecarboxylation event and culminating in transfer of the acetyl moiety to the E2 component. Monitoring the kinetics of E1 and its loop variants at various solution viscosities, we show that the rate of a chemical step is modulated by loop dynamics. A cysteine-free E1 construct was site-specifically labeled on the inner loop (residues 401-413), and the EPR nitroxide label revealed ligand-induced conformational dynamics of the loop and a slow "open <--> close" conformational equilibrium in the unliganded state. An (19)F NMR label placed at the same residue revealed motion on the millisecond-second time scale and suggested a quantitative correlation of E1 catalysis and loop dynamics for the 200,000-Da protein. Thermodynamic studies revealed that these motions may promote covalent addition of substrate to the enzyme-bound thiamin diphosphate by reducing the free energy of activation. Furthermore, the global dynamics of E1 presumably regulate and streamline the catalytic steps of the overall complex by inducing an entirely entropic (nonmechanical) negative cooperativity with respect to substrate binding at higher temperatures. Our results are consistent with, and reinforce the hypothesis of, coupling of catalysis and regulation with enzyme dynamics and suggest the mechanism by which it is achieved in a key branchpoint enzyme in sugar metabolism.
authors.affiliation: Department of Chemistry, Rutgers, The State University of New Jersey, Newark, NJ 07102, USA.
authors.forename: Sachin
authors.initials: S
authors.lastname: Kale
authors.forename: Gözde
authors.initials: G
authors.lastname: Ulas
authors.forename: Jaeyoung
authors.initials: J
authors.lastname: Song
authors.forename: Gary W
authors.initials: GW
authors.lastname: Brudvig
authors.forename: William
authors.initials: W
authors.lastname: Furey
authors.forename: Frank
authors.initials: F
authors.lastname: Jordan
mesh_terms: D019943:Amino Acid Substitution / Q000235:genetics; D001665:Binding Sites / Q000235:genetics; D002384:Catalysis; D002942:Circular Dichroism; D004578:Electron Spin Resonance Spectroscopy; D029968:Escherichia coli Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D007700:Kinetics; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D011487:Protein Conformation; D017433:Protein Structure, Secondary / Q000235:genetics; D011768:Pyruvate Dehydrogenase Complex / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity / Q000235:genetics; D013816:Thermodynamics; D014783:Viscosity
chemical_list: D029968:Escherichia coli Proteins; D008024:Ligands; D011768:Pyruvate Dehydrogenase Complex; C453599:pyruvate dehydrogenase multienzyme complex E1