title: How fast is protein hydrophobic collapse?
abstract: One of the most recurring questions in protein folding refers to the interplay between formation of secondary structure and hydrophobic collapse. In contrast with secondary structure, it is hard to isolate hydrophobic collapse from other folding events. We have directly measured the dynamics of protein hydrophobic collapse in the absence of competing processes. Collapse was triggered with laser-induced temperature jumps in the acid-denatured form of a simple protein and monitored by fluorescence resonance energy transfer between probes placed at the protein ends. The relaxation time for hydrophobic collapse is only approximately equal to 60 ns at 305 K, even faster than secondary structure formation. At higher temperatures, as the protein becomes increasingly compact by a stronger hydrophobic force, we observe a slowdown of the dynamics of collapse. This dynamic hydrophobic effect is a high-temperature analogue of the dynamic glass transition predicted by theory. Our results indicate that in physiological conditions many proteins will initiate folding by collapsing to an unstructured globule. Local motions will presumably drive the following search for native structure in the collapsed globule.
authors.affiliation: Department of Chemistry and Biochemistry, Center for Biomolecular Structure and Organization, University of Maryland, College Park, MD 20742, USA.
authors.forename: Mourad
authors.initials: M
authors.lastname: Sadqi
authors.forename: Lisa J
authors.initials: LJ
authors.lastname: Lapidus
authors.forename: Victor
authors.initials: V
authors.lastname: Muñoz
mesh_terms: D055592:Biophysical Phenomena; D001703:Biophysics; D031541:Fluorescence Resonance Energy Transfer; D006863:Hydrogen-Ion Concentration; D057927:Hydrophobic and Hydrophilic Interactions; D007655:Ketoglutarate Dehydrogenase Complex / Q000737:chemistry; D008958:Models, Molecular; D019906:Nuclear Magnetic Resonance, Biomolecular; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D011506:Proteins / Q000737:chemistry*; D013816:Thermodynamics
chemical_list: D011506:Proteins; D007655:Ketoglutarate Dehydrogenase Complex