LIPID PEPTIDE INTERFACE - VALINE CONFORMATION AND DYNAMICS IN THE GRAMICIDIN CHANNEL

High-resolution dynamic and structural characterizations have been ach ieved for each of the valine side chains of the gramicidin channel whi le solubilized in hydrated lipid bilayers. The characterizations have been achieved by H-2 NMR spectra of both oriented and unoriented sampl es obtained at 36 and 5 degrees C, respectively. Powder patterns displ aying intermediate time frame averaging provide dynamic information, a nd quadrupole splittings from aligned samples provide orientational co nstraints for the side chain structure, Librational amplitudes for eac h site throughout the side chain have also been characterized. Val(6) and Val(8) are shown to be fixed in rotameric states, potentially cons training two of the indole rings and the functionally important indole dipole moment orientations. Val(1) and Val(7) undergo three-state jum p motions, The jump frequencies increase from the microsecond to nanos econd time frame upon increasing the temperature through the lipid pha se transition. For the same temperature range, there is no evidence fo r changes in conformational state populations. Despite small differenc es in the substate populations for the two residues, the motions may b e loosely coupled as indicated by the high-resolution structure.