Pulsed ESR Double Resonance (PELDOR) Spectroscopy: Application to spin-labeled peptides

Abstract

The applicability of a new pulsed ESR technique (PELDOR) for obtaining the weak dipoledipole interactions between spin labels is demonstrated, from which the distances up to several tens angstrom can be derived. The results of the spin labeled trichogin GA IV analogues studies are discussed in this chapter. The intramolecular distances between spin labels are estimated for a series of frozen solutions of double-labeled trichogin GA IV analogues. The distances for 27or 310 helical conformations of the trichogin peptides are obtained. It is shown that the particular peptide chain conformation and its fraction depend on peptide structure and the polar properties of a solvent. Byanalyzing of the intermolecular dipole-dipole interactions between spin labels the aggregates of these peptides have been revealed in a series of frozen weakly polar solutions. It is shown that the number of peptide molecules in aggregates tends to four. The 310 helical conformation is detected for the trichogin molecules inside the aggregates. An aggregate model of four 310-helical trichogin molecules has been proposed here.