FD COAT PROTEIN-STRUCTURE IN MEMBRANE ENVIRONMENTS - STRUCTURAL DYNAMICS OF THE LOOP BETWEEN THE HYDROPHOBIC TRANS-MEMBRANE HELIX AND THE AMPHIPATHIC INPLANE HELIX

By performing multidimensional solution NMX experiments on micelle sam ples it was possible to determine the structure of the membrane-bound form of fd coat protein based on short-range distance and dihedral ang le constraints using distance geometry and simulated annealing calcula tions. Its dynamics were described by N-15 relaxation measurements (T- 1, T-2, heteronuclear nuclear Overhauser enhancement (NOE)) fitted wit h the Lipari-Szabo model-free formalism adapted for the transmembrane and in-plane helices of a membrane protein. The overall correlation ti me of the protein in micelles was found to be similar to 9 ns, and the local motion of each backbone N-H vector was described by an order pa rameter and an effective correlation time. The 50 residue protein has an amphipathic alpha-helix (residues 7 to 16) and a hydrophobic alpha- helix (residues 27 to 44), which were found to be approximately perpen dicular on the basis of NOEs in the residues that connect the two heli ces. The residues connecting the helices are of particular interest in membrane proteins, and in this case the loop consists of two turns. T he relaxation data show the presence of an extra motion in the amphipa thic alpha-helix on the nanosecond timescale and additional flexibilit y of several residues in the loop connecting the two helices. (C) 1997 Academic Press Limited.