ESR spectra reflect local and global mobility in a short spin-labeled peptide throughout the alpha-helix----coil transition.

摘要: A series of short alanine-based synthetic peptides (16 or 17 residues) have previously been shown to exhibit an anomalously high degree alpha-helicity [Marqusee, S., et al. (1989) Proc. Natl. Acad. Sci. U.S.A. 86, 5286-5290; Marqusee, & Baldwin, R.L. (1987) 84, 8898-8902]. These are ideal models for extracting position-dependent structural and dynamic information. Using the methanethiosulfonate nitroxide spin label (MTSSL), we labeled analogue salt-bridge-stabilized "i+4" peptide, called "i+4c", which has a specific attachment site created by replacing central alanine with cysteine. Circular dichroism (CD) spectra demonstrate that i+4c-MTSSL peptide retains nearly same helicity as original i+4 peptide. The ESR indicate no significant aggregation. were acquired throughout helix-coil transition temperature variation. From motionally narrowed spectra, extracted rotational correlation times label. Parallel measurements circular enabled us relate these parameters directly fractional helicity. For comparison, followed similar procedure MTSSL-labeled glutathione (GS-MTSSL), tripeptide does not form alpha-helix. Our results interpreted in terms local tumbling volume, V(L), reflects portion reorients At helicity, V(L) is volume expected 17-residue helix.