Sequence-specific liquid crystallinity of collagen model peptides. I. Transmission electron microscopy studies of interfacial collagen gels

The conformation, crystal structure and self-assembly behavior of three pep tides with collagen-like repetitive sequences [(1) peptide GAPGPP: (Glu)(5) (Gly-Ala-Pro-Gly-Pro-Pro)(6)(Glu)(5); (2) peptide GVPGPP: (Glu)(5)(Gly-Val- Pro-Gly-Pro-Pro)(6)(Glu)(5); and (3) peptide GAPGPA: (Glu)(5)(Gly-Ala-Pro-G ly-Pro-Ala)(6)(Glu)(5)] were compared. The peptides were characterized usin g transmission Electron microscopy, electron diffraction, environmental sca nning electron microscopy, and Fourier transform ir spectroscopy in order t o determine how the molecular geometry dictated by each sequence affects th e spontaneous generation of long-range ordered structures. Samples of each peptide, at ambient temperature and at 5 degrees C, were examined as films dried from aqueous solution, air-water interfacial films, and chloroform-wa ter interfacial films, Peptide GAPGPP prepared at 5 degrees C and dried fro m bulk solution, was found to have a collagen-like triple-helical structure . A sinusoidally textured gel, suggestive of cholesteric behavior was obser ved for peptides GAPGPP and GVPGPP at the aqueous chloroform interface at 5 degrees C. Peptide GAPGPA also formed a gel, but less reproducibly and the sinusoidal texture was not as well defined. The periodicities of the sinus oidal textures were reproducibly 10 mu m for peptide GAPGPP, 7 mu m for pep tide GVPGPP, and 6 mu m for peptide GAPGPA. The differences in rile periodi city of the banded structure and in the crystallization behavior of the thr ee peptides is attributed to differences in the symmetry of the preferred p acking arrangement for each peptide, as evidenced by electron diffraction f rom crystallites that coexist with the sinusoidal gel. These differences ar e believed to be a measure of the effective symmetry and shape of the molec ular cross section. (C) 2000 John Wiley & Sons, Inc.