Structure Characterization of a Disordered Peptide\nUsing In-Droplet Hydrogen/Deuterium Exchange Mass Spectrometry and\nMolecular Dynamics

In-droplet hydrogen/deuterium\nexchange (HDX)-mass spectrometry\n(MS) experiments have been conducted for peptides of highly varied\nconformational type. A new model is presented that combines the use\nof protection factors (PF) from molecular dynamics (MD) simulations\nwith intrinsic HDX rates (<i>k</i><sub>int</sub>) to obtain\na structure-to-reactivity calibration curve. Using the model, the\nrelationship of peptide structural flexibility and HDX reactivity\nfor different peptides is elucidated. Additionally, the model is used\nto describe the degree of conformational flexibility and structural\nbias for the disease-relevant Nt17 peptide; although highly flexible,\nintrinsically primed for facile conversion to α-helical conformation\nupon binding with molecular partners imparts significant in-droplet\nHDX protection for this peptide. In the future, a scale may be developed\nwhereby HDX reactivity is predictive of the degree of structural flexibility\nand bias (propensity to form 2° structural elements such as α-helix,\nβ-sheet, and β-turn) for intrinsically disordered regions\n(IDRs). Such structural resolution may ultimately be used for high-throughput\nscreening of IDR structural transformation(s) upon binding of ligands\nsuch as drug candidates.