Modeling Peptide-binding Interactions and Polymer-binding Interactions and their Role in Mass Spectrometry.

摘要

As a first project, collision-induced dissociation experiments were carried out using electrospray ionisation mass spectrometry on gas phase complexes involving different poly(methylmetacrylate) oligomers with three amino acids: glycine, leucine, and phenylalanine. After acquiring breakdown diagrams, RRKM modeling was used to fit the experimental data in order to obtain the 0 K activation energy (E0) and the entropy of activation (Delta ‡S). These thermodynamic data were then used to understand the competing dissociation channels observed (except for gas phase complexes involving glycine that had only one dissociation channel). Molecular dynamics simulated annealing calculations were carried on the gas phase complexes to understand further the energetic and entropic effects involved as well as the 3D conformation of these complexes. Valuable insight information was found on the 3D conformations, on a qualitative level. Using rotational constants and vibrational harmonic frequencies, it was possible to evaluate the entropy variation between the experimentally observed competing channels. Reasonable agreement was found between the experimental and theoretical variations of entropies. Finally, the proton affinity of poly(methylmetacrylate) oligomers is being discussed. Even though no absolute values for the proton affinity were found, the experimental and computational results help to understand the variation that accompanies the oligomers length.;The second project presents the development an efficient and reproducible screening method for identifying low molecular weight compounds that bind to amyloid beta peptides (Abeta) peptides using electrospray ionization mass spectrometry (ESI-MS). Low molecular weight (LMW) compounds capable of interacting with soluble Abeta may be able to modulate/inhibit the Abeta aggregation process and serve as potential disease-modifying agents for Alzheimer's disease. The present approach was used to rank the binding affinity of a library of compounds to Abeta1-40 peptide. The results obtained show that low molecular weight compounds bind similarly to Abeta1-42, Abeta1-40, as well as Abeta1-28 peptides and they underline the critical role of Abeta peptide charge motif in binding at physiological pH. Finally, some elements of structure-activity relationship (SAR) involved in the binding affinity of homotaurine to soluble Abeta peptides are discussed. As a third project, the gas phase binding of small molecules to the Abeta1-40 peptide generated by electrospray ionization has been explored with collision-induced dissociation mass spectrometry and kinetic rate theory. This project presents a simple procedure used to theoretically model the experimental breakdown diagrams for the Abeta1-40 peptide complexed with a series of aminosulfonate small molecules, namely homotaurine, 3-cyclohexylamino-2-hydroxy-1-propanesulfonic acid (CAPSO), 3-(1,3,4,9-tetrahydro-2H-beta-carbolin-2-yl) propane-1-sulfonic acid, 3-(1,3,4,9-tetrahydro-2H-beta-carbolin-2-yl)butane-1-sulfonic acid, and 3-(cyclohexylamino) propane-1-sulfonic acid. An alternative method employing an extrapolation procedure for the microcanonical rate constant, k(E), is also discussed.