Rotational diffusion and intermolecular collisions of a spin labeled alpha-helical peptide determined by electron spin echo spectroscopy

• Published in: Biophysical journal Vol. 63; no. 4; pp. 917 - 925
• Main Authors: Miick, S.M., Millhauser, G.L.
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Elsevier Inc 01.10.1992; Biophysical Society; The Biophysical Society
• Subjects: Alanine; Amino Acid Sequence; Biological and medical sciences; conformation; Conformational dynamics in molecular biology; electron spin echo spectroscopy; Fundamental and applied biological sciences. Psychology; helix; Mathematics; Models, Structural; Molecular biophysics; Molecular Sequence Data; peptides; Peptides - chemistry; Protein Structure, Secondary; Spectrum Analysis - methods; Intermolecular interaction; Spin labelling; Reorientation diffusion; Peptides; EPR spectrometry; Molecular dynamics; Molecule molecule collision; Spin echo; Helical structure
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/S0006-3495(92)81690-9

Short peptides that are composed mainly of alanine have recently been shown to form alpha-helices in aqueous solution at low temperature (Marqusee, S., and R. L. Baldwin. 1987. Proc. Natl. Acad. Sci. 84:8898–8902; Marqusee, S., V. H. Robbins, and R. L. Baldwin. 1989. Proc. Natl. Acad. Sci. USA. 86:5286–5290). These peptides are excellent models for probing structure and dynamics in isolated helical domains. In previous work we have designed and synthesized spin labeled analogs of these helix-forming peptides and we have shown that these analogs retain the folding characteristics of the parent peptide (Todd, A. P., and G. L. Millhauser. 1991. Biochemistry. 30:5515–5523). Using conventional continuous wave electron spin resonance (CW ESR) we have further shown that local motion is more pronounced near the helix amino terminus than in the central region as the peptide is thermally unfolded (Miick, S. M., A. P. Todd, and G. L. Millhauser. 1991. Biochemistry. 30:9498–9503). In this present work we use electron spin echo (ESE) spectroscopy to further refine our understanding of the solution dynamics of the 3K-8 peptide, which is a 16-mer with a nitroxide spin label attached at position 8. We find that the spin echo decays are well described by a single exponential function and that the determined correlation times are close to those previously derived from CW experiments. Variable concentration ESE experiments have directly revealed Heisenberg spin exchange (HSE) interactions and we find that the interpeptide collision rate is near to that expected for a free species in solution.