Nitroxide Side-Chain Dynamics in a Spin-Labeled Helix-Forming Peptide Revealed by High-Frequency (139.5-GHz) EPR Spectroscopy

• Published in: Journal of magnetic resonance (1997) Vol. 139; no. 2; pp. 281 - 286
• Main Authors: Bennati, M., Gerfen, G.J., Martinez, G.V., Griffin, R.G., Singel, D.J., Millhauser, G.L.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.08.1999
• Subjects: Amino Acid Sequence; anisotropic motion; Anisotropy; Electron Spin Resonance Spectroscopy; EPR; high frequency; peptide; Peptides - chemistry; Protein Conformation; side-chain dynamics; Spin Labels; Temperature; side-chain dynamics; peptide; high frequency; anisotropic motion; EPR
• ISSN: 1090-7807; 1096-0856
• DOI: 10.1006/jmre.1999.1769

High-frequency electron paramagnetic resonance (EPR) spectroscopy has been performed on a nitroxide spin-labeled peptide in fluid aqueous solution. The peptide, which follows the single letter sequence , was reacted with the methanethiosulfonate spin label at the cysteine sulfur. The spin sensitivity of high-frequency EPR is excellent with less than 20 pmol of sample required to obtain spectra with good signal-to-noise ratios. Simulation of the temperature-dependent spectral lineshapes reveals the existence of local anisotropic motion about the nitroxide N–O bond with a motional anisotropy τ⊥/τ∥ (≡ N) approaching 2.6 at 306 K. Comparison with previous work on rigidly labeled peptides suggests that the spin label is reorienting about its side-chain tether. This study demonstrates the feasibility of performing 140-GHz EPR on biological samples in fluid aqueous solution.