title: Thermodynamic analysis of the chemotactic protein from Escherichia coli, CheY.
abstract: CheY, the 129 amino acid chemotactic protein from Escherichia coli, is a good model for studies of folding of parallel alpha/beta proteins. We report here the thermodynamic characterization of the wild-type CheY at different pH values and in different buffers and denaturation conditions. The denaturation of CheY by urea monitored by circular dichroism and fluorescence fits the two-state unfolding model. The stability of the protein is ionic strength dependent, probably due to the presence of three Asp residues in very close proximity in its active site. The presence of a Mg2+ ion, which seems to interact with Asp 13 in the active site, stabilizes the native structure by up to 6.9 kJ mol-1. The CheY maximum stability (31.7 +/- 2.1 kJ mol-1), without magnesium, is reached at pH 5.1. Analysis of scanning calorimetry data has shown that temperature-induced unfolding of CheY is not a two-state process and proceeds through a highly populated intermediate state, corresponding to protein dimers, as was subsequently confirmed by direct cross-linking experiments. According to circular dichroism, fluorescence, nuclear magnetic resonance, and ANS binding experiments, this "intermediate dimer" at pH 2.5 exhibits all known characteristics of the "molten globule" state. The reversible dimerization of "molten globules" might explain such peculiarities as the increased stability or the cooperative unfolding found for the molten globule state of some proteins.
authors.affiliation: European Molecular Biology Laboratory, Heidelberg, Germany.
authors.forename: V V
authors.initials: VV
authors.lastname: Filimonov
authors.forename: J
authors.initials: J
authors.lastname: Prieto
authors.forename: J C
authors.initials: JC
authors.lastname: Martinez
authors.forename: M
authors.initials: M
authors.lastname: Bruix
authors.forename: P L
authors.initials: PL
authors.lastname: Mateo
authors.forename: L
authors.initials: L
authors.lastname: Serrano
mesh_terms: D000817:Anilino Naphthalenesulfonates / Q000378:metabolism; D001426:Bacterial Proteins; D001483:Base Sequence; D002021:Buffers; D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D004926:Escherichia coli / Q000737:chemistry*; D029968:Escherichia coli Proteins; D005456:Fluorescent Dyes / Q000378:metabolism; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D013058:Mass Spectrometry; D008565:Membrane Proteins / Q000737:chemistry* / Q000235:genetics / Q000302:isolation & purification; D000072236:Methyl-Accepting Chemotaxis Proteins; D008956:Models, Chemical; D008969:Molecular Sequence Data; D008970:Molecular Weight; D016296:Mutagenesis; D009994:Osmolar Concentration; D011489:Protein Denaturation; D017510:Protein Folding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry; D017421:Sequence Analysis; D012997:Solvents; D013050:Spectrometry, Fluorescence; D013816:Thermodynamics
chemical_list: D000817:Anilino Naphthalenesulfonates; D001426:Bacterial Proteins; D002021:Buffers; D029968:Escherichia coli Proteins; D005456:Fluorescent Dyes; D008565:Membrane Proteins; D000072236:Methyl-Accepting Chemotaxis Proteins; D011994:Recombinant Proteins; D012997:Solvents; C000607606:cheY protein, E coli; C027132:1-anilino-8-naphthalenesulfonate