Beta-pleated sheets in oligopeptide crystals.

Many oligopeptide crystals show the beta-pleated sheet structures. Both parallel and antiparallel chain pleated sheets are found, and also both ideal (flat) and heavily twisted sheets are found. The structural parameters, such as the T (NC alpha C') angles, the torsion angles (phi and psi), the fiber axis periods, the hydrogen bond lengths, and the interchain spacings, are studied. Some of them deviate significantly from those proposed by Pauling & Corey ()Proc. Natl. Acad. Sci. US (1953), 39, 253-256). In the heavily twisted sheets, the twists are large than those in the globular proteins, and each two neighboring chains are almost perpendicular with each other, preserving the beta-sheet type hydrogen bond system. The torsion angles in the twisted sheets are rather close to those of the poly (L-proline) II helix. It also is discussed that the T (NA alpha C') angles sometimes deviate by almost 5 degrees from the standard value depending on the structures of the main and side chains.