title: Reshaping the folding energy landscape by chloride salt: impact on molten-globule formation and aggregation behavior of carbonic anhydrase.
abstract: During chemical denaturation different intermediate states are populated or suppressed due to the nature of the denaturant used. Chemical denaturation by guanidine-HCl (GuHCl) of human carbonic anhydrase II (HCA II) leads to a three-state unfolding process (Cm,NI=1.0 and Cm,IU=1.9 M GuHCl) with formation of an equilibrium molten-globule intermediate that is stable at moderate concentrations of the denaturant (1-2 M) with a maximum at 1.5 M GuHCl. On the contrary, urea denaturation gives rise to an apparent two-state unfolding transition (Cm=4.4 M urea). However, 8-anilino-1-naphthalene sulfonate (ANS) binding and decreased refolding capacity revealed the presence of the molten globule in the middle of the unfolding transition zone, although to a lesser extent than in GuHCl. Cross-linking studies showed the formation of moderate oligomer sized (300 kDa) and large soluble aggregates (>1000 kDa). Inclusion of 1.5 M NaCl to the urea denaturant to mimic the ionic character of GuHCl leads to a three-state unfolding behavior (Cm,NI=3.0 and Cm,IU=6.4 M urea) with a significantly stabilized molten-globule intermediate by the chloride salt. Comparisons between NaCl and LiCl of the impact on the stability of the various states of HCA II in urea showed that the effects followed what could be expected from the Hofmeister series, where Li+ is a chaotropic ion leading to decreased stability of the native state. Salt addition to the completely urea unfolded HCA II also led to an aggregation prone unfolded state, that has not been observed before for carbonic anhydrase. Refolding from this state only provided low recoveries of native enzyme.
authors.affiliation: IFM-Department of Chemistry, Linköping University, SE-581 83 Linköping, Sweden.
authors.forename: Kristina
authors.initials: K
authors.lastname: Borén
authors.forename: Hannah
authors.initials: H
authors.lastname: Grankvist
authors.forename: Per
authors.initials: P
authors.lastname: Hammarström
authors.forename: Uno
authors.initials: U
authors.lastname: Carlsson
mesh_terms: D000817:Anilino Naphthalenesulfonates / Q000737:chemistry; D024402:Carbonic Anhydrase II / Q000737:chemistry*; D003432:Cross-Linking Reagents / Q000737:chemistry; D029968:Escherichia coli Proteins / Q000737:chemistry; D006801:Humans; D018021:Lithium Chloride / Q000737:chemistry*; D011487:Protein Conformation; D011489:Protein Denaturation; D017510:Protein Folding; D012965:Sodium Chloride / Q000737:chemistry*; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics; D014364:Tryptophan / Q000737:chemistry; D014508:Urea / Q000737:chemistry
chemical_list: D000817:Anilino Naphthalenesulfonates; D003432:Cross-Linking Reagents; D029968:Escherichia coli Proteins; D012965:Sodium Chloride; D014364:Tryptophan; D014508:Urea; D024402:Carbonic Anhydrase II; D018021:Lithium Chloride