High-Resolution, Real-Space Imaging of Conformational Structures of Poly-L-Proline Helixes

Authors

N. J. Zheng, Rice University
G. Rau, Baylor College of Medicine
C. F. Hazlewood, Baylor College of Medicine
C. Rau, Rice University

Abstract

In 1954, Edsall postulated that the imino-acid proline, which is a frequently found constituent of protein molecules, is a key determinant to the three-dimensional architecture of proteins. It not only should play a fundamental role in stabilizing helical structures of polypeptides, it should allow for sharp bends and even for a complete reversal of the direction of a helix looping back on itself. No direct evidence has yet been published to prove this prediction. Using scanning tunneling microscopy, we have presented high-resolution, real-space images of two conformations of poly-L-proline, where one structure clearly exhibits the predicted 180° back-folding behavior. The measured length, 1.89 nm, of the repeating unit cells agrees with available X-ray data for poly-L-proline I with cis-peptide bonds. We further observe aggregated poly-L-proline II, consisting of highly-ordered, periodically and parallel-linked trans-peptide chains which are 2.4 nm apart from each other. Stacking of these aggregates with their orientation rotated by 90° is also observed.

Recommended Citation

Zheng, N. J.; Rau, G.; Hazlewood, C. F.; and Rau, C. (1991) "High-Resolution, Real-Space Imaging of Conformational Structures of Poly-L-Proline Helixes," Scanning Microscopy: Vol. 5: No. 3, Article 5.
Available at: https://digitalcommons.usu.edu/microscopy/vol5/iss3/5