A NOVEL, MULTILAYER STRUCTURE OF A HELICAL PEPTIDE

X-ray diffraction analysis at 1.5 Angstrom resolution has confirmed th e helical conformation of a de novo designed 18-residue peptide. Howev er, the crystal structure reveals the formation of continuous molecula r layers of parallel-packed amphiphilic helices as a result of much mo re extensive helix-helix interactions than predicted. The crystal pack ing arrangement, by virtue of distinct antiparallel packing interactio ns, segregates the polar and apolar surfaces of the helices into discr ete and well-defined interfacial regions. An extensive ''ridges-into-g rooves'' interdigitation characterizes the hydrophobic interface, wher eas an extensive network of salt bridges and hydrogen bonds dominates the corresponding hydrophilic interface.