title: O2 penetration and proton burial depth in proteins: applicability to fold family recognition.
abstract: Paramagnetically induced relaxation effects of O2 and the nitroxide 4-hydroxy TEMPO were measured for the amide protons of perdeuterated rubredoxin from the hyperthermophilic archaeon Pyrococcus furiosus and the mesophilic bacterium Clostridium pasteurianum. For both O2 and the impermeant nitroxide, the induced relaxation at the static solvent inaccessible amide sites is dominated by long-range interactions with the paramagnetic species in the bulk aqueous phase. The upper bound of O2 solubility in the internal matrix of the rubredoxins is one-tenth that of the bulk aqueous phase. Furthermore, the difference between the oxygen solubilities inside the two rubredoxins is at most 1% that of bulk water O2 solubility, suggesting that there are only modest differences in this measure of fluidity for the mesophile vs hyperthermophile protein interiors. Calculations based on the assumption of a paramagnet uniformly distributed on the protein exterior yield accurate predictions at nearly all amide sites for the minimum relaxation value observed from either the O2 or nitroxide data. Model calculations indicate that the readily obtained paramagnetically induced relaxation effects should prove effective in recognition of structural homology for proteins that are too widely diverged for sequence-based recognition.
authors.affiliation: Wadsworth Center and Department of Biomedical Sciences, University at Albany-SUNY, Empire State Plaza, Albany, New York 12201-0509, USA.
authors.forename: Griselda
authors.initials: G
authors.lastname: Hernández
authors.forename: Ching-Ling
authors.initials: CL
authors.lastname: Teng
authors.forename: Robert G
authors.initials: RG
authors.lastname: Bryant
authors.forename: David M
authors.initials: DM
authors.lastname: LeMaster
mesh_terms: D001426:Bacterial Proteins; D003497:Cyclic N-Oxides / Q000737:chemistry; D019906:Nuclear Magnetic Resonance, Biomolecular / Q000379:methods; D010100:Oxygen / Q000737:chemistry* / Q000378:metabolism; D017510:Protein Folding; D020027:Pyrococcus furiosus / Q000737:chemistry / Q000378:metabolism; D012416:Rubredoxins / Q000737:chemistry* / Q000378:metabolism; D013113:Spin Labels
chemical_list: D001426:Bacterial Proteins; D003497:Cyclic N-Oxides; D012416:Rubredoxins; D013113:Spin Labels; C077196:rubredoxin protein, Clostridium pasteurianum; D010100:Oxygen; C001803:tempol