title: Probing water density and dynamics in the chaperonin GroEL cavity.
abstract: ATP-dependent binding of the chaperonin GroEL to its cofactor GroES forms a cavity in which encapsulated substrate proteins can fold in isolation from bulk solution. It has been suggested that folding in the cavity may differ from that in bulk solution owing to steric confinement, interactions with the cavity walls, and differences between the properties of cavity-confined and bulk water. However, experimental data regarding the cavity-confined water are lacking. Here, we report measurements of water density and diffusion dynamics in the vicinity of a spin label attached to a cysteine in the Tyr71 → Cys GroES mutant obtained using two magnetic resonance techniques: electron-spin echo envelope modulation and Overhauser dynamic nuclear polarization. Residue 71 in GroES is fully exposed to bulk water in free GroES and to confined water within the cavity of the GroEL-GroES complex. Our data show that water density and translational dynamics in the vicinity of the label do not change upon complex formation, thus indicating that bulk water-exposed and cavity-confined GroES surface water share similar properties. Interestingly, the diffusion dynamics of water near the GroES surface are found to be unusually fast relative to other protein surfaces studied. The implications of these findings for chaperonin-assisted folding mechanisms are discussed.
authors.affiliation: Department of Chemistry and Biochemistry, University of California Santa Barbara, California 93106, United States.
authors.forename: John M
authors.initials: JM
authors.lastname: Franck
authors.forename: Miri
authors.initials: M
authors.lastname: Sokolovski
authors.forename: Naama
authors.initials: N
authors.lastname: Kessler
authors.forename: Erez
authors.initials: E
authors.lastname: Matalon
authors.forename: Michal
authors.initials: M
authors.lastname: Gordon-Grossman
authors.forename: Song-I
authors.initials: SI
authors.lastname: Han
authors.forename: Daniella
authors.initials: D
authors.lastname: Goldfarb
authors.forename: Amnon
authors.initials: A
authors.lastname: Horovitz
mesh_terms: D001483:Base Sequence; D018835:Chaperonin 10 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D018834:Chaperonin 60 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D017510:Protein Folding; D013113:Spin Labels; D014867:Water / Q000378:metabolism
chemical_list: D018835:Chaperonin 10; D018834:Chaperonin 60; D029968:Escherichia coli Proteins; D013113:Spin Labels; D014867:Water