Trifluoroethanol stabilizes a helix-turn-helix motif in equine infectious-anemia-virus trans-activator protein.
The solution structure of the 75-amino-acid trans-activator (Tat) protein of the equine infectious-anemia virus in trifluoroethanol-containing solution was determined by two-dimensional and three-dimensional nuclear magnetic resonance spectroscopy, resulting in a total of 838 nuclear-Over-hauser-enhancement distance restraints, and restrained molecular-dynamics simulations. In contrast to the recently determined structure of this protein in trifluoroethanol-free pH 6.3 solution, the hydrophobic core and the adjacent basic RNA-binding region of the protein showed well-defined alpha-helical secondary structure in trifluoroethanol-containing solution. The helical regions comprise those parts of the molecule whose helix-forming tendencies were noted earlier in trifluoroethanol-free solution. Two helices (Gln38-Arg43 and Asp48-Ala64) are connected by a tight type-II turn centered at the strictly conserved Gly46 leading to a helix-turn-helix motif in the core and basic region of the protein. A third helix (Thr9-Asn13) is located in the less well defined N-terminal part of the protein. These observations may support the notion that the protein adopts a helical structure in the RNA-binding region on complex formation. Although the secondary-structure elements become better defined in trifluoroethanol-containing solution, the opposite is true for the hydrophobically stabilized tertiary structure. This adds a caveat to studies of protein structures in trifluoroethanol-containing solution in general.
Lehrstuhl für Biopolymere und Bayreuther Institut für Makromolekülforschung (BIMF), Universität Bayreuth, Germany.
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D000595:Amino Acid Sequence; D004355:Drug Stability; D015696:Gene Products, tat / Q000737:chemistry* / Q000235:genetics; D018257:Helix-Loop-Helix Motifs / Q000235:genetics; D004860:Infectious Anemia Virus, Equine / Q000737:chemistry* / Q000235:genetics; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012996:Solutions; D013816:Thermodynamics; D014270:Trifluoroethanol
D015696:Gene Products, tat; D012996:Solutions; D014270:Trifluoroethanol