title: Rotational dynamics of HIV-1 nucleocapsid protein NCp7 as probed by a spin label attached by peptide synthesis.
abstract: 2,2,6,6-Tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid (TOAC) spin label was attached at the N-terminal position to interrogate the dynamics of the HIV-1 nucleocapsid Zn-finger protein, NCp7. NCp7 is a 6.4-kDa 55-mer critical to the recognition, packaging, and efficient reverse transcription of viral RNA that has stem-loop structures, such as the RNA stem-loop 3 used in this work. The NCp7, made by solid-phase peptide synthesis with TOAC incorporated into the alpha-carbon backbone at the N-terminal "0" position, showed analytical purity and biological activity. Electron Paramagnetic Resonance (EPR) spectra of the N-terminal TOAC indicated rapid temperature-sensitive motion of the probe (< or =0.33 ns correlation time) on the flexible N-terminal segment. This N-terminal TOAC-NCp7 reported a RNA-NCp7 interaction at a 1:1 ratio of NCp7 to RNA, which caused the tumbling time to be slowed from about 0.3 ns to about 0.5 ns. NCp7 is a largely disordered protein that adapts to its RNA targets. However, as shown by circular dichroism, > or =90% trifluoroethanol [(TFE), an alpha-helix enhancer] caused the TOAC-NCp7 without zinc in its fingers to change to a fully helical conformation, while the TOAC spin label was concurrently reporting a tumbling time of well over a nanosecond, as the N-terminal TOAC became inflexibly enfolded. Even with TFE present, the existence of intact Zn-finger regions in NCp7 prevented complete formation of helical structure, as shown by circular dichroism, and decreased the N-terminal TOAC tumbling time, as shown by EPR. This study demonstrated TOAC at the N-terminal of NCp7 to be a reporter for the considerable conformational lability of NCp7. (
authors.affiliation: Department of Biochemistry, Molecular Biology, and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA.
authors.forename: Zhiwen
authors.initials: Z
authors.lastname: Zhang
authors.forename: Xiangmei
authors.initials: X
authors.lastname: Xi
authors.forename: Charles P
authors.initials: CP
authors.lastname: Scholes
authors.forename: Christine B
authors.initials: CB
authors.lastname: Karim
mesh_terms: D000595:Amino Acid Sequence; D004578:Electron Spin Resonance Spectroscopy; D015497:HIV-1 / Q000737:chemistry; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D012399:Rotation; D015032:Zinc / Q000378:metabolism; D016335:Zinc Fingers; D054301:gag Gene Products, Human Immunodeficiency Virus / Q000737:chemistry*
chemical_list: C071884:NCP7 protein, Human immunodeficiency virus 1; D054301:gag Gene Products, Human Immunodeficiency Virus; D015032:Zinc