title: EspB from enterohaemorrhagic Escherichia coli is a natively partially folded protein.
abstract: The structural properties of EspB, a virulence factor of the Escherichia coli O157 type III secretion system, were characterized. Far-UV and near-UV CD spectra, recorded between pH 1.0 and pH 7.0, show that the protein assumes alpha-helical structures and that some tyrosine tertiary contacts may exist. All tyrosine side-chains are exposed to water, as determined by acrylamide fluorescence quenching spectroscopy. An increase in the fluorescence intensity of 8-anilinonaphthalene-1-sulfonate was observed at pH 2.0 in the presence of EspB, whereas no such increase in fluorescence was observed at pH 7.0. These data suggest the formation of a molten globule state at pH 2.0. Destabilization of EspB at low pH was shown by urea-unfolding transitions, monitored by far-UV CD spectroscopy. The result from a sedimentation equilibrium study indicated that EspB assumes a monomeric form at pH 7.0, although its Stokes radius (estimated by multiangle laser light scattering) was twice as large as expected for a monomeric globular structure of EspB. These data suggest that EspB, at pH 7.0, assumes a relatively expanded conformation. The chemical shift patterns of EspB 15N-1H heteronuclear single quantum correlation spectra at pH 2.0 and 7.0 are qualitatively similar to that of urea-unfolded EspB. Taken together, the properties of EspB reported here provide evidence that EspB is a natively partially folded protein, but with less exposed hydrophobic surface than traditional molten globules. This structural feature of EspB may be advantageous when EspB interacts with various biomolecules during the bacterial infection of host cells.
authors.affiliation: Department of Developmental Infectious Diseases, Research Institute, Osaka Medical Center for Maternal and Child Health, Japan.
authors.forename: Daizo
authors.initials: D
authors.lastname: Hamada
authors.forename: Tomoaki
authors.initials: T
authors.lastname: Kato
authors.forename: Takahisa
authors.initials: T
authors.lastname: Ikegami
authors.forename: Kayo N
authors.initials: KN
authors.lastname: Suzuki
authors.forename: Makoto
authors.initials: M
authors.lastname: Hayashi
authors.forename: Yoshikatsu
authors.initials: Y
authors.lastname: Murooka
authors.forename: Takeshi
authors.initials: T
authors.lastname: Honda
authors.forename: Itaru
authors.initials: I
authors.lastname: Yanagihara
mesh_terms: D020106:Acrylamide / Q000737:chemistry; D000595:Amino Acid Sequence; D000817:Anilino Naphthalenesulfonates / Q000737:chemistry; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry*; D002942:Circular Dichroism; D019453:Escherichia coli O157 / Q000737:chemistry*; D029968:Escherichia coli Proteins; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D011489:Protein Denaturation; D017510:Protein Folding; D017433:Protein Structure, Secondary; D017386:Sequence Homology, Amino Acid; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D014508:Urea / Q000737:chemistry
chemical_list: D000817:Anilino Naphthalenesulfonates; D001425:Bacterial Outer Membrane Proteins; C087863:EaeB protein, E coli; D029968:Escherichia coli Proteins; D020106:Acrylamide; C027132:1-anilino-8-naphthalenesulfonate; D014508:Urea