title: Kinetics of the self-aggregation and film formation of poly-L-proline at high temperatures explored by circular dichroism spectroscopy.
abstract: Poly-L-proline has been used as a model system for various purposes over a period of more than 60 years. Its relevance among the protein/peptide community stems from its use as a reference system for determining the conformational distributions of unfolded peptides and proteins, its use as a molecular ruler, and from the pivotal role of proline residues in conformational transitions and protein-protein interactions. While several studies indicate that polyproline can aggregate and precipitate in aqueous solution, a systematic study of the aggregation process is still outstanding. We found, by means of UV-circular dichroism and IR measurements, that polyproline is predominantly monomeric at room temperature at millimolar concentrations. Upon heating, the polypeptide stays in its monomeric state until the temperature reaches a threshold of ca. 60 degrees C. At higher temperatures, the peptide aggregates as a film on the inside surface of the employed cuvette. The process proceeds on a time scale of 10(3) s and can best be described by a bi-exponential relaxation function. The respective CD and IR spectra are qualitatively different from the canonical spectra of polyproline in aqueous solution, and are indicative of a highly packed state.
authors.affiliation: Department of Chemistry, Drexel University, Philadelphia, PA 19104, USA.
authors.forename: Lonna
authors.initials: L
authors.lastname: Tooke
authors.forename: Laura
authors.initials: L
authors.lastname: Duitch
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Measey
authors.forename: Reinhard
authors.initials: R
authors.lastname: Schweitzer-Stenner
mesh_terms: D002942:Circular Dichroism; D006358:Hot Temperature; D007700:Kinetics; D010455:Peptides / Q000737:chemistry*; D013499:Surface Properties; D013997:Time Factors
chemical_list: D010455:Peptides; C011083:polyproline