title: High-resolution, real-space imaging of conformational structures of poly-L-proline helixes.
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 degrees 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 degrees is also observed.
authors.affiliation: Department of Physics, Rice University, Houston, TX 77251-1892.
authors.forename: N J
authors.initials: NJ
authors.lastname: Zheng
authors.forename: G
authors.initials: G
authors.lastname: Rau
authors.forename: C F
authors.initials: CF
authors.lastname: Hazelwood
authors.forename: C
authors.initials: C
authors.lastname: Rau
mesh_terms: D016252:Microscopy, Scanning Tunneling / Q000379:methods*; D010455:Peptides; D011487:Protein Conformation
chemical_list: D010455:Peptides; C011083:polyproline