Confirmation of the solution structure of tyrocidine a using perturbation of proton relaxation rates by nitroxide spin labels

Abstract

The spin–lattice relaxation rate enhancements of the protons of tyrocidine A upon addition of 2,2,6,6-tetramethylpiperidin-1-oxyl (TEMPO) were analysed in solution and were shown to be consistent with the peptide conformation. The effects on tyrocidine A proton spin–lattice relaxation rates for three TEMPO derivatives in two different solvents have also been studied in order to obtain information about the influence of TEMPO substituents on nitroxide-biomolecule interactions. The neutral free radical TEMPO exhibits less specificity in its interaction with tyrocidine A than its derivatives and, hence, it is the most suitable probe for generally investigating conformational moieties of biomolecules in solution. By corollary, charged nitroxides should be probes of the microenvironment surrounding the specific site of interaction.