Dr. Baldwin proposes to measure, for the first time, exchange rates of individual peptide NH protons within single, isolated alpha- helices. A nuclear magnetic resonance (NMR) technique will be used, based on 15N spectral editing of the one-dimensional proton spectrum. A single peptide NH will be 15N-labeled by chemical synthesis of the peptide, and 15N spin echo difference spectroscopy will be used to give the 1H spectrum of the single 15N-labeled peptide NH. A trial experiment demonstrating the feasibility of this approach has been made. The new method will be used to test the basic assumptions of helix-random coil transition theory, and also to provide background information about exchange rates of amide protons in single alpha-helices, for use in interpreting data on protein folding intermediates. %%% The proposed experiments will provide a new technique for obtaining structural information about short peptides, for example, when the peptide is complexed with a specific receptor. Currently there is wide interest in " peptide libraries", both in the biotechnology field and in biomedical science generally. Methodologies have been developed for synthesizing astronomical numbers of different short peptide sequences and then for selecting a small number of sequences that can bind specifically to a receptor in a signal transduction pathway. This method will provide an important tool for characterizing the structure of a peptide in a peptide-receptor complex. As pointed out above, the method also has direct application to the problem of characterizing structures of kinetic intermediates on the pathway of protein folding.
