title: Coulomb forces control the density of the collapsed unfolded state of barstar.
abstract: Although it has been recently shown that unfolded polypeptide chains undergo a collapse on transfer from denaturing to native conditions, the forces determining the dynamics and the size of the collapsed form have not yet been understood. Here, we use single-molecule fluorescence resonance energy transfer experiments on the small protein barstar to characterize the unfolded chain in guanidinium chloride (GdmCl) and urea. The unfolded protein collapses on decreasing the concentration of denaturants. Below the critical concentration of 3.5 M denaturant, the collapse in GdmCl leads to a more dense state than in urea. Since it is known that GdmCl suppresses electrostatic interactions, we infer that Coulomb forces are the dominant forces acting in the unfolded barstar under native conditions. This hypothesis is clearly buttressed by the finding of a compaction of the unfolded barstar by addition of KCl at low urea concentrations.
authors.affiliation: Institute of Biochemistry and Biotechnology, Kurt-Mothes Strasse 3, 06120 Halle, Germany. hagen.hofmann@biochemtech.uni-halle.de
authors.forename: Hagen
authors.initials: H
authors.lastname: Hofmann
authors.forename: Ralph P
authors.initials: RP
authors.lastname: Golbik
authors.forename: Maria
authors.initials: M
authors.lastname: Ott
authors.forename: Christian G
authors.initials: CG
authors.lastname: Hübner
authors.forename: Renate
authors.initials: R
authors.lastname: Ulbrich-Hofmann
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000235:genetics; D031541:Fluorescence Resonance Energy Transfer; D005456:Fluorescent Dyes / Q000378:metabolism; D014644:Genetic Variation; D019791:Guanidine / Q000494:pharmacology; D016297:Mutagenesis, Site-Directed; D010957:Plasmids; D011489:Protein Denaturation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D055672:Static Electricity; D014508:Urea / Q000494:pharmacology
chemical_list: D001426:Bacterial Proteins; D005456:Fluorescent Dyes; C057438:barstar protein, Bacillus amyloliquefaciens; D014508:Urea; D019791:Guanidine