title: Experimental identification of downhill protein folding.
abstract: Theory predicts the existence of barrierless protein folding. Without barriers, folding should be noncooperative and the degree of native structure should be coupled to overall protein stability. We investigated the thermal unfolding of the peripheral subunit binding domain from Escherichia coli's 2-oxoglutarate dehydrogenase multienzyme complex (termed BBL) with a combination of spectroscopic techniques and calorimetry. Each technique probed a different feature of protein structure. BBL has a defined three-dimensional structure at low temperatures. However, each technique showed a distinct unfolding transition. Global analysis with a statistical mechanical model identified BBL as a downhill-folding protein. Because of BBL's biological function, we propose that downhill folders may be molecular rheostats, in which effects could be modulated by altering the distribution of an ensemble of structures.
authors.affiliation: Department of Chemistry and Biochemistry and Center for Biomolecular Structure and Organization, University of Maryland, College Park, MD 20742, USA.
authors.forename: Maria M
authors.initials: MM
authors.lastname: Garcia-Mira
authors.forename: Mourad
authors.initials: M
authors.lastname: Sadqi
authors.forename: Niels
authors.initials: N
authors.lastname: Fischer
authors.forename: Jose M
authors.initials: JM
authors.lastname: Sanchez-Ruiz
authors.forename: Victor
authors.initials: V
authors.lastname: Muñoz
mesh_terms: D000217:Acyltransferases / Q000737:chemistry*; D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D004926:Escherichia coli / Q000201:enzymology; D005453:Fluorescence; D031541:Fluorescence Resonance Energy Transfer; D006863:Hydrogen-Ion Concentration; D007655:Ketoglutarate Dehydrogenase Complex / Q000737:chemistry*; D008956:Models, Chemical; D008958:Models, Molecular; D009097:Multienzyme Complexes / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D021122:Protein Subunits; D013696:Temperature; D013816:Thermodynamics
chemical_list: D009097:Multienzyme Complexes; D021122:Protein Subunits; D007655:Ketoglutarate Dehydrogenase Complex; D000217:Acyltransferases; C021515:dihydrolipoamide succinyltransferase