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.

Huntingtin fibrils with different toxicity, structure, and seeding potential can be reversibly interconverted

“…4a, blue line). Similar transitions have been reported and interpreted in terms of temperature dependent oligomerization or film formation of the polyP peptides (Tooke et al, 2010). To test for film formation in our polyP preparations, we removed the liquid from the CD cuvette at high temperature and recorded the CD spectra ( Fig.…”

“…4a, red line). Much of CD spectrum remained after liquid removal indicating that the peptides no longer resided in solution but rather formed a film on the surface of the glass (Tooke et al, 2010). Interestingly, polyP film formation causes a red shift in the minimum of its CD spectrum that is reminiscent of the difference between T and N-fibrils.…”

Fibril polymorphism affects immobilized non-amyloid flanking domains of huntingtin exon1 rather than its polyglutamine core

“…The partly overlapping resonance frequencies expected for α-helices, β-sheet polyQ amyloid and PPII-helical oligoproline (oligoPro) are indicated in Fig. 2g (refs 13 , 37 , 41 , 42 , 43 , 44 ). The differentiating FTIR signals show most similarity to signals expected for the PRD, but an unambiguous assignment is challenging.…”

Exploring hydrophobicity limits of polyproline helix with oligomeric octahydroindole‐2‐carboxylic acid

“…The aggregation of polyproline structures has only been sporadically reported in the literature; however, in the case of oligo‐Oic peptides, this process is apparently driven by the hydrophobicity of the cyclohexane side chain decoration. The precipitate formed by the crude PO9 peptide was soluble in dichloromethane, similar to all of the other oligo‐Oic peptides studied here.…”