Direct Analysis of Proteins from Solutions with High Salt Concentration Using Laser Electrospray Mass Spectrometry

Abstract

The detection of lysozyme, or a mixture of lysozyme, cytochrome c, and myoglobin, from solutions with varying salt concentrations (0.1 to 250 mM NaCl) is compared using laser electrospray mass spectrometry (LEMS) and electrospray ionization-mass spectrometry (ESI-MS). Protonated protein peaks were observed up to a concentration of 250 mM NaCl in the case of LEMS. In the case of ESI-MS, a protein solution with salt concentration > 0.5 mM resulted in predominantly salt-adducted features, with suppression of the protonated protein ions. The constituents in the mixture of proteins were assignable up to 250 mM NaCl for LEMS and were not assignable above a NaCl concentration of 0.5 mM for ESI. The average sodium adducts (< n >) bound to the 7+ charge state of lysozyme for LEMS measurements from salt concentrations of 2.5, 25, 50, and 100 mM NaCl are 1.71, 5.23, 5.26, and 5.11, respectively. The conventional electrospray measurements for lysozyme solution containing salt concentrations of 0.1, 1, 2, and 5 mM NaCl resulted in < n > of 2.65, 6.44, 7.57, and 8.48, respectively. LEMS displays an approximately two orders of magnitude higher salt tolerance in comparison with conventional ESI-MS. The non-equilibrium partitioning of proteins on the surface of the charged droplets is proposed as the mechanism for the high salt tolerance phenomena observed in the LEMS measurements. Graphical Abstract ᅟ.

Speciation Studies of Bifunctional 3-Hydroxy-4-Pyridinone Ligands in the Presence of Zn2+ at Different Ionic Strengths and Temperatures

“…The observation of the sodium and potassium adducts is very common in ESI-MS spectra, possible due to background impurities and to the considerable presence, in some cases, of ionic medium NaCl in solution [32]. Furthermore, an intensity decrease of the [ H ( L5 ) + H] + peak with ionic strength increase was noticed, in particular at I = 1.00 mol L −1 , due to a signal suppression attributable to the ionic medium effect, leading to a significant salt-adducted species formation [33,34,35].…”

Native Mass Spectrometry of Membrane Proteins

“…Matrix-assisted laser desorption/ionization (MALDI) has been limited for native MS because it typically uses denaturing sample preparation conditions such as organic matrices and drying, requiring covalent cross-linking to stabilize noncovalent complexes for analysis . Recently, studies have demonstrated the capability for MALDI to preserve noncovalent interactions for proteins using liquid matrices. , Other laser-based methods that have been shown to preserve native-like protein features include desorption by impulsive vibrational excitation (DIVE) and laser electrospray ionization (LEMS), but these techniques have not been applied to membrane proteins to our knowledge.…”

Rapid detection and quantification of aminoglycoside phosphorylation products using direct‐infusion high‐resolution and ultra‐high‐performance liquid chromatography/mass spectrometry

“…A more recent development, ambient ionization, pioneered with the development of desorption ionization mass spectrometry (DESI), has been shown to tolerate highly complex samples without a chromatographic separation due to the unique sample introduction and ionization mechanism of the technique . This development impelled various ambient ionization techniques to include electrospray laser desorption ionization (ELDI), laser ablation electrospray ionization (LAESI), and laser electrospray mass spectrometry (LEMS), which have all demonstrated high tolerance for complex samples without separation or sample preparation. It should be noted that these techniques are just beginning extensive validation investigations and considerable research is needed to confirm their abilities to identify and quantitate trace level analytes from complex biological samples without sample preparation or separation.…”