STRUCTURE AND DYNAMICS OF THE NEUTROPHIL DEFENSINS NP-2, NP-5, AND HNP-1 - NMR-STUDIES OF AMIDE HYDROGEN-EXCHANGE KINETICS

The exchange kinetics for the slowly exchanging amide hydrogens in thr ee defensins, rabbit NP-2, rabbit NP-5, and human HNP-1, have been mea sured over a range of pH at 25 degrees C using 1D and 2D NMR methods. These NHs have exchange rates 10(2) to 10(5) times slower than rates f rom unstructured model peptides. The observed distribution of exchange rates under these conditions can be rationalized by intramolecular hy drogen bonding of the individual NHs, solvent accessibility of the NHs , and local fluctuations in structure. The temperature dependencies of NH chemical shifts (NH temperature coefficients) were measured for th e defensins and these values are consistent with the defensin structur e. A comparison is made between NH exchange kinetics, NH solvent acces sibility, and NH temperature coefficients of the defensins and other g lobular proteins. Titration of the histidine side chain in NP-2 was ex amined and the results are mapped to the three-dimensional structure. (C) 1994 Wiley-Liss, Inc.