The Role of Salt Bridges on Gas Phase Protein Structures

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The Chemical Measurement and Imaging Program in the Division of Chemistry, supports Professors Rachele Loo and Joseph Loo at the University of California-Los Angeles (UCLA). With growing interest in biotech and pharmaceutical fields to develop therapeutic protein-based drugs, the need to understand the exact structures of large biomolecules is expanding. Despite the growing interest in this field, there remains a large gap in the fundamental understanding of how the structure of a protein and/or protein complex dictates the measurements. This research seeks to fill this knowledge gap by detailing how making the measurement itself can change the protein or protein complex. Mass spectrometry (MS) techniques are used to analyze biological samples that are important to the pharmaceutical and biotechnology industries. The broader impacts of this work include providing fundamental knowledge of protein structure that are important to disease research in medicine. The research team designs chemical analysis laboratories for advanced high school students in South Los Angeles? Biotech Career Pathways Program. This program exposes students to life science careers and provides technical skills in viable STEM related fields used in biotechnology, medicine, and government regulatory agencies.The extent of stabilization that ion pairs (salt bridges) provide to gas phase proteins and protein complexes delivered by electrospray ionization (ESI)-MS is addressed by monitoring the charge state-dependent activation and dissociation behaviors of gas-phase complexes. Considerable evidence exists that not all opposing charges are neutralized in ESI; therefore, limited activation can reorient negatively charged side chains into positions well-placed to interact with cationic sites, replacing solvent molecule "glue" formerly stabilizing subunit interfaces with salt bridges. The goals of this research include demonstrating the means by which the opposite charge contributions to ESI-generated ions can be manipulated. The project also tests trends predicted by models; e.g., effects on gas phase cross-sections, on the products and charge-state distributions arising from collision induced dissociation of gas phase assemblies, and on the relationship between gas and solution phase structures of intrinsically-disordered proteins. The investigations test whether the charge state-dependent activation and dissociation behaviors observed in ESI-MS reflect how Coulomb repulsion destabilizes high charge state species.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.