Chemistry Proposal Defense Seminar – Haley Schramm

About the event

Title: Quantitative Evaluation of Ion-Solvation Using Simultaneous Selective Ion Clustering and Hydrogen/Deuterium Exchange

Abstract: Ion mobility spectrometry (IMS) offers a complementary gas-phase separation to mass spectrometry (MS). Coupling the techniques has gained traction as a tool for structural biology to make inferences on conformational landscapes of gas-phase biopolymers. While ion mobility is a comparatively low-resolution method, separation capacity can be increased by ion-neutral clustering via a reactive drift gas dopant. Clusters with organic vapors have been found to be site-specific and structurally selective offering a useful tool for gas-phase ion structures. Another established ion-neutral reaction for structural determination is gas-phase hydrogen/deuterium exchange (HDX). Analyte ion hydrogens may exchange for deuterium if they are accessible on the surface, and a shift in the isotopic window can be measured by MS. While most structural studies of biopolymers focus on native state structures, sampling nonnative intermediates offers insight into structural transitions pertinent to the folding process and protein conformational diseases such as Alzheimer’s disease. Initial folding experiments found that some transitions were stabilized by localized solvation using thermodynamic parameters. Here, a new method to probe the thermodynamics of local solvation with simultaneous HDX is presented. Foundational studies with amino acids using an atmospheric pressure drift tube IMS with deuterated methanol demonstrates increased deuterium incorporation with less intrinsic error than alternative methods for quantitative HDX kinetics of gas-phase ions. Many derivatized amino acids are commercially available allowing for further fundamental experiments probing site-specific evaluation of HDX and ion-neutral clustering. Results from the foundational experiments can then be applied to larger species such as peptides and proteins. While organic solvents have shown to destabilize native-like secondary structures in solution, preliminary work in the gas-phase between peptides and organic solvents showed to selectively stabilize charge states for various peptides. By deriving thermodynamic parameters for the localized solvation and complementary HDX kinetics, energy landscapes linking native and non-native peptide and protein structures can be generated with increased speed and tunability.