Protein structure evolution in liquid DESI as revealed by selective noncovalent adduct protein probing

Abstract

Previous experiments based on charge state distributions have suggested that liquid desorption electrospray ionization (DESI) is capable of preserving solution phase protein structure during transfer to the gas phase (Journal of the American Society for Mass Spectrometry 21 (2010) 1730-1736). In order to examine this possibility more carefully, we have utilized selective non-covalent adduct protein probing (SNAPP) to evaluate protein structural evolution in both liquid DESI and standard ESI under a variety of conditions. Experiments with cytochrome c (Cytc) demonstrated that methanol induced conformational shifts previously observed with ESI are also easily observed with liquid DESI. However, undesirable acid-induced unfolding becomes apparent at very high concentrations of methanol in liquid DESI due to acetic acid in the spray solvent, suggesting that there are conditions under which liquid DESI will not preserve solution phase structure. The effects of ammonium acetate buffer on liquid DESI SNAPP experiments were examined by monitoring structural changes in myoglobin. Heme retention and SNAPP distributions were both preserved better in liquid DESI than traditional ESI, suggesting superior performance for liquid DESI in buffered conditions. Finally, liquid DESI SNAPP was used to study the natively disordered proteins α, β, and γ synuclein with SNAPP. α-Synuclein, the main component of fibrils found in patients with Parkinson’s disease, yielded a significantly different SNAPP distribution compared to β and γ synuclein. This difference is indicative of highly accessible protonated basic side chains, a property known to promote fibril formation in proteins.

Integration of online digestion and electrolytic reduction with mass spectrometry for rapid disulfide-containing protein structural analysis

“…It would reduce signal intensity without using any organic solvent. Interestingly, DESI offers a solution to this problem by using methanol/water (50:50, v/v) containing 1.0% formic acid as the spray solvent [51,52]. Indeed, in this case, the DESI signal of the digested insulin in water containing 1% formic acid was found to be about 4 times higher than the signal of electrosonic spray ionization (ESSI [53], a variant form of electrospray ionization) of the same sample (spectra not shown).…”

Measuring Protein–Ligand Interactions Using Liquid Sample Desorption Electrospray Ionization Mass Spectrometry

“…It also allows for the development of submillisecond time-resolved mass spectrometry for the study of fast reaction kinetics. 31 Results from protein analysis by Julian’s group 32 and our lab 33 suggests that protein measurements by DESI can be enhanced by the liquid sample DESI option, especially for the analysis of native proteins because an acidic spray solvent can be used without denaturation of the protein structure.…”

Gas-phase microsolvation of ubiquitin: investigation of crown ether complexation sites using ion mobility-mass spectrometry

“…This agrees well with another study where CE complexes with ubiquitin lysine-to-asparagine mutants were analysed via selective noncovalent adduct protein probing mass spectrometry (SNAPP-MS). [40][41][42] Here, the authors investigate the changing adduct distribution in mass spectra for mutants with only one lysine replaced in the sequence and reveal that intramolecular interactions, such as salt bridges and hydrogen bonds, can hamper the coordination of 18C6 to protonated lysine residues. 29 …”