Atmospheric Pressure Ultraviolet Laser Desorption and Ionization from Liquid Samples for Native Mass Spectrometry.

Oliver J Hale,Rainer Cramer

doi:10.1021/acs.analchem.9b03875

Oliver J Hale, Rainer Cramer

Open Access

https://doi.org/10.1021/acs.analchem.9b03875

Copy DOI

Journal: Analytical Chemistry	Publication Date: Oct 25, 2019
Citations: 6	License type: cc-by

Affiliation: University of Reading

Abstract

Understanding protein structure is vital for evaluating protein interactions with drugs, proteins, and other ligands. Native mass spectrometry (MS) is proving to be invaluable for this purpose, enabling analysis of “native-like” samples that mimic physiological conditions. Native MS is usually performed by electrospray ionization (ESI) with its soft ionization processes and the generation of multiply charged ions proving favorable for conformation retention and high mass analysis, respectively. There is scope to expand the currently available toolset, specifically to other soft ionization techniques such as soft laser desorption, for applications in areas like high-throughput screening and MS imaging. In this Letter, observations made from native MS experiments using an ultraviolet (UV) laser-based ion source operating at atmospheric pressure are described. The ion source is capable of producing predominately multiply charged ions similar to ESI. Proteins and protein complexes were analyzed from a native-like sample droplet to investigate the technique. Ion mobility-mass spectrometry (IM-MS) measurements showed that folded protein conformations were detected for ions with low charge states. This observation indicates the source is suitable for native MS analysis and should be further developed for higher mass analysis in the future.

Highlights

Understanding protein structure is vital for evaluating protein interactions with drugs, proteins, and other ligands
In this Letter, we demonstrate native mass spectrometry (MS) analysis of the monomeric protein hen egg white lysozyme (HEWL) and other proteins using a simple atmospheric pressure (AP)-MALDI ion source with a low-cost UV laser, generating multiply charged MALDI protein ions on a commercial high-performance QTOF instrument with ion mobility separation
It is reasonable to suggest that the laser in the AP-MALDI ion source used here plays a fundamentally limited role in the ionization itself but is practically an extremely convenient and highly controllable method of introducing small, nebulized volumes of liquid sample to the heated inlet. This initial report of native-like sample analysis with a UV-APMALDI ion source presents an alternative to the usual electrospray ionization (ESI) MS methodologies used for native MS

Summary

Introduction

Understanding protein structure is vital for evaluating protein interactions with drugs, proteins, and other ligands. Ion mobility-mass spectrometry (IM-MS) measurements showed that folded protein conformations were detected for ions with low charge states. This observation indicates the source is suitable for native MS analysis and should be further developed for higher mass analysis in the future. The soft ionization techniques electrospray ionization (ESI) and nanoESI are used extensively for analysis of samples in “native-like” conditions by mass spectrometry (native MS). As present under physiological conditions, may be preserved This is important for ion mobility-mass spectrometry (IM-MS) instruments, which are capable of gas-phase evaluation of the 3-dimensional protein ion structure.[3,4] Values for collisional cross sections (CCSs) may be determined from IM-MS experiments, allowing ion conformations to be compared between systems and techniques. Liquid extraction surface analysis (LESA) has been demonstrated for the analysis of native proteins directly from tissue sections.[6]

Methods

Results

Conclusion