Vibrational circular dichroism of adenosine crystals.

Adenosine is one of the building blocks of nucleic acids and other biologically important molecules. Spectroscopic methods have been among the most utilized techniques to study adenosine and its derivatives. However, most of them deal with adenosine in solution. Here, we present the first vibrational circular dichroism (VCD) spectroscopic study of adenosine crystals in solid state. Highly regular arrangement of adenosine molecules in a crystal resulted in a strongly enhanced supramolecular VCD signal originating from long-range coupling of vibrations. The data suggested that adenosine crystals, in contrast to guanosine ones, do not imbibe atmospheric water. Relatively large dimensions of the adenosine crystals resulted in scattering and substantial orientational artifacts affecting the spectra. Several strategies for tackling the artifacts have been proposed and tested. Atypical features in IR absorption spectra of crystalline adenosine (e.g., extremely low absorption in mid-IR spectral range) were observed and attributed to refractive properties of adenosine crystals.

Glucagon-like peptide 1 aggregates into low-molecular-weight oligomers off-pathway to fibrillation.

The physical stability of peptide-based drugs is of great interest to the pharmaceutical industry. Glucagon-like peptide 1 (GLP-1) is a 31-amino acid peptide hormone, the analogs of which are frequently used in the treatment of type 2 diabetes. We investigated the physical stability of GLP-1 and its C-terminal amide derivative, GLP-1-Am, both of which aggregate into amyloid fibrils. While off-pathway oligomers have been proposed to explain the unusual aggregation kinetics observed previously for GLP-1 under specific conditions, these oligomers have not been studied in any detail. Such states are important as they may represent potential sources of cytotoxicity and immunogenicity. Here, we identified and isolated stable, low-molecular-weight oligomers of GLP-1 and GLP-1-Am, using size-exclusion chromatography. Under the conditions studied, isolated oligomers were shown to be resistant to fibrillation or dissociation. These oligomers contain between two and five polypeptide chains and they have a highly disordered structure as indicated by a variety of spectroscopic techniques. They are highly stable with respect to time, temperature, or agitation despite their noncovalent character, which was established using liquid chromatography-mass spectrometry and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These results provide evidence of stable, low-molecular-weight oligomers that are formed by an off-pathway mechanism which competes with amyloid fibril formation.