Solution conformations of human growth hormone releasing factor: comparison of the restrained molecular dynamics and distance geometry methods for a system without long-range distance data

A series of three-dimensional structures of the 1-29 fragment of human growth hormone releasing factor in trifluoroethanol have been determined by molecular dynamics and distance geometry methods. The resulting structures satisfy information from nuclear Overhauser effect (NOE) distance data and an empirical potential energy function. Although the polypeptide was found to have an ordered structure in all simulations, the NOE data were not sufficient for global convergence to a unique three-dimensional geometry. Several satisfactory structures have been determined, all of which are extended conformations consisting of a short beta-strand and two alpha-helices (residues 6-13 and residues 16-29) connected by short segments of less well defined secondary structure. Because of the lack of NOE data connecting the helix segments, their relative orientation is not uniquely determined.