title: Solute effects on spin labels at an aqueous-exposed site in the flap region of HIV-1 protease.
abstract: The effects of solutes on spin-label mobility and protein conformation have been investigated with X-band continuous-wave and pulsed electron paramagnetic resonance (EPR) spectroscopy for spin labels attached to an aqueous-exposed site in the beta-hairpin flap region of HIV-1 protease. Specifically, we examined the effects of glycerol, sucrose, PEG3000, and Ficoll400 for four commonly used nitroxide spin labels and found that the largest perturbations to the EPR line shapes occur for solutions containing PEG3000 and glycerol. From comparisons of the spectral line shapes and distance distribution profiles of spin-labeled HIV-1 protease with and without inhibitor, it was concluded that solutes such as glycerol and PEG3000 alter the line shapes of the spin label in the beta-hairpin flaps of HIV-1 PR by modulation of spin-label mobility through changes in preferential interactions with the solutes. It is noteworthy that the high osmolality of the 40% glycerol solution did not alter the conformation of the flaps as determined from pulsed EPR distance measurements.
authors.affiliation: Department of Chemistry, University of Florida, P.O. Box 117200, Gainesville, Florida 32611, USA.
authors.forename: Luis
authors.initials: L
authors.lastname: Galiano
authors.forename: Mandy E
authors.initials: ME
authors.lastname: Blackburn
authors.forename: Angelo M
authors.initials: AM
authors.lastname: Veloro
authors.forename: Marco
authors.initials: M
authors.lastname: Bonora
authors.forename: Gail E
authors.initials: GE
authors.lastname: Fanucci
mesh_terms: D001665:Binding Sites; D004578:Electron Spin Resonance Spectroscopy; D005362:Ficoll / Q000737:chemistry*; D005990:Glycerol / Q000737:chemistry*; D016333:HIV Protease / Q000737:chemistry* / Q000378:metabolism*; D009589:Nitrogen Oxides / Q000737:chemistry; D009994:Osmolar Concentration; D011092:Polyethylene Glycols / Q000737:chemistry*; D011487:Protein Conformation; D013113:Spin Labels; D013395:Sucrose / Q000737:chemistry*; D013997:Time Factors; D014783:Viscosity; D014867:Water / Q000737:chemistry
chemical_list: D009589:Nitrogen Oxides; D013113:Spin Labels; D014867:Water; D005362:Ficoll; D011092:Polyethylene Glycols; D013395:Sucrose; D016333:HIV Protease; C514803:p16 protease, Human immunodeficiency virus 1; D005990:Glycerol