Native Ion Mobility-Mass Spectrometry Techniques for Characterizing the Structure and Lipid Binding of Bacterial Pore-Forming Toxins
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Date
2020-09-24
Authors
Wilson, Jesse
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Publisher
University of Oregon
Abstract
Membrane proteins constitute a large portion of the protein and protein complexes found across life and perform a diverse range of critical functions such as transport of molecules and signaling across lipid bilayers. However, due to the instability of membrane proteins in solution without a membrane-like environment and the heterogeneity of such samples, study of these types of complexes can be incredibly challenging using conventional techniques such as X-ray crystallography, nuclear magnetic resonance, or electron microscopy.
In the last couple of decades, native mass spectrometry with electrospray ionization has emerged as an alternative technique in structural biology for the study of soluble and membrane protein complexes alike. The unique advantage of native mass spectrometry is that non-covalent interactions can be retained from solution to the gas-phase environment of the mass spectrometer. Meaning that stoichiometry information from membrane proteins such as the oligomeric state and small molecule and lipid binding can be investigated based on the mass distributions of these complexes. When coupled with ion mobility spectrometry, not only is stoichiometry information obtained, but also size and shape information that can be utilized to better understand the structures of biomolecules from solution and compared to structures determined using the above-mentioned techniques.
Here, studies in native mass spectrometry technique development are presented in the investigation of bacterial transmembrane pore forming toxins. As membrane proteins, these complexes pose several challenges to native mass spectrometry due to the inherent heterogeneity and polydispersity in mass caused by the associated membrane mimetic used, such as detergent micelles or lipoprotein nanodiscs. Using native mass spectrometry αHL from Staphylococcus aureus is found to form both hexameric and heptameric complexes in solution simultaneously, while other structural techniques had predominantly identified the heptameric complex.
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Keywords
detergent micelle, ion mobility, membrane protein, nano-electrospray ionization, nanodisc, native mass spectrometry