Towards a breakthrough in applications of vibrational optical activity: an experimental study of the environmental effects on protein spectra
20 November 2018
Campus Groenenborger, V.008 - Groenenborgerlaan 171 - 2020 Antwerpen (route: UAntwerpen, Campus Groenenborger
Organization / co-organization:
Department of Chemistry
Evelien Van de Vondel
Christian Johannessen & Wouter Herrebout
PhD defence Evelien Van de Vondel - Faculty of Science, Department of Chemistry
The work in this thesis tried to expand the possible applications of VOA for the study of the structural properties of proteins. Until now, most systems studied with VOA are relatively simple. Firstly, the sensitivity of ROA towards small changes in the structural properties of proteins in crowded environments was explored, an important contribution towards the understanding of the behavior of intrinsically disordered proteins in physiological conditions. It was demonstrated that the structural effect, induced by the presence of crowding agents and determined by means of ROA, depends on the used crowding agent and its concentration. It was indicated that the effect of F70 on the structural properties of dP-Acas is a superposition of both the crowding effect, similar to the effect of D70, and a specific interaction, similar to the effect of sucrose. It was also demonstrated that the sensitivity of ROA towards small conformational changes is sufficient to track small structural changes throughout a titration with different concentrations of crowding agent. The use of a CID plot to interpret complicated ROA data was introduced, enabling the researcher to identify individual contributions to the spectrum, as long as this interpretation is performed with a critical eye, due to risk of over interpretation of the data.
Secondly, it was demonstrated that VCD is sensitive towards the higher order structural elements of fibrils in a nondestructive way, as VCD was sensitive towards the mutual alignment and the length of the fibrils of alpha-synuclein, amongst other through a manifestation of an enhanced signal. In a systematic study, using the peptide KLVFF and its halogenated derivatives, an enhancement of the ROA signal, without resonance with the laser, was also for the first time experimentally observed. Contrary to literature, it was determined that the enhanced signals in VOA most likely do not originate in the structure of the fibril architecture, as similar shapes in the VCD spectra were observed for different fibril architectures. However, the results suggest that the presence of an enhanced VCD spectrum can be a measure for the directional properties of the intermolecular bonds, e.g. the halogen bond for the presented data. This observation suggests that VCD is capable of identifying similarities on a molecular level between fibrils with different architectures in a non-destructive manner.
In conclusion, all results in this thesis indicate that both ROA and VCD are capable of analyzing complex samples, and providing information not accessible to other techniques.