Development of Electrospray Ionization‐Mass Spectrometry for Analysis of Water Soluble and Membrane Proteins and Educational Protocols for an Analytical Chemistry Class

Native mass spectrometry (MS) is a branch of MS analysis in which the structure of the target analytes of interest are kept intact and remaining in their “native” functional structure (as much as possible). This approach was made possible by the development of electrospray ionization (ESI), a soft ionization technique that does not fragment the target analyte during the ionization process while inducing multiple charging. The multiply charged biomolecules, in turn, can be subjected to fragmentation via collisional activation with a non-reactive gas such as nitrogen. This approach of combining native MS with fragmentation-based analysis, termed native topdown MS analysis, can be applied to large biomolecules such as membrane proteins to gain structural insights. Membrane proteins present unique challenges to conventional high-resolution structural techniques due to their hydrophobic nature. However, they are responsible for various physiological phenomena and account for 60% of known druggable targets in the cell. Thus, there is a need for an approach that can overcome issues with membrane protein analysis while complementing other biophysical techniques used to probe protein structure. Here, how native top-down MS can play this role is presented. The effects of non-ionic saccharide-based detergents, a commonly used class of detergents for membrane protein solubilization, on the resulting charge states of soluble proteins is investigated to gain insights into the mechanism of ESI. The MS-fragmentation patterns from collisionally activated dissociation of membrane proteins and membrane protein-lipid complexes are compared. How new insights into the lipid binding sites can be gained by detecting lipid-bound MS-fragments is presented. The result of the study indicates that native top-down MS analysis can provide unique structural insights for membrane proteins and their non-covalent interactions. When the analytical goal is to investigate the atomic composition of the target analyte, an ionization approach in which the sample is fully atomized before MS analysis is preferred instead. Inductively coupled plasma ionization, which atomizes and ionizes the sample via a plasma, can be coupled with MS analysis (ICP-MS) to quantify heavy metal contamination in complex samples. A protocol for ICP-MS analysis of commercial fish products for mercury contamination detection developed to aid an analytical chemistry class for instruction of undergraduate chemistry students is presented