In situ mass spectrometry analysis of intact proteins and protein complexes from biological substrates.

Oliver J. Hale,Helen J. Cooper

doi:10.1042/bst20190793

Abstract

Advances in sample preparation, ion sources and mass spectrometer technology have enabled the detection and characterisation of intact proteins. The challenges associated include an appropriately soft ionisation event, efficient transmission and detection of the often delicate macromolecules. Ambient ion sources, in particular, offer a wealth of strategies for analysis of proteins from solution environments, and directly from biological substrates. The last two decades have seen rapid development in this area. Innovations include liquid extraction surface analysis, desorption electrospray ionisation and nanospray desorption electrospray ionisation. Similarly, developments in native mass spectrometry allow protein–protein and protein–ligand complexes to be ionised and analysed. Identification and characterisation of these large ions involves a suite of hyphenated mass spectrometry techniques, often including the coupling of ion mobility spectrometry and fragmentation techniques. The latter include collision, electron and photon-induced methods, each with their own characteristics and benefits for intact protein identification. In this review, recent developments for in situ protein analysis are explored, with a focus on ion sources and tandem mass spectrometry techniques used for identification.

Highlights

Analysis of proteins in situ has become a focus in the development of many mass spectrometer technologies, especially ion sources
mass spectrometry imaging (MSI) has typically been the realm of matrix-assisted laser desorption/ ionisation (MALDI) MS [1], an ionisation technique that is usually performed under vacuum conditions; MALDI MSI generally requires complementary methods to identify the proteins detected since MALDI-generated protein ions are predominantly in low charge states and are not amenable to efficient fragmentation for top-down identification [2]
Developments in soft and ambient ionisation techniques that do produce highly charged ions are showing their value for intact protein analysis, and without the time-consuming sample preparation required for MALDI

Summary

Review Article

Ion sources and mass spectrometer technology have enabled the detection and characterisation of intact proteins. Developments in native mass spectrometry allow protein–protein and protein–ligand complexes to be ionised and analysed. Identification and characterisation of these large ions involves a suite of hyphenated mass spectrometry techniques, often including the coupling of ion mobility spectrometry and fragmentation techniques. The latter include collision, electron and photon-induced methods, each with their own characteristics and benefits for intact protein identification. Recent developments for in situ protein analysis are explored, with a focus on ion sources and tandem mass spectrometry techniques used for identification

Introduction

Ambient ionisation

Liquid junction surface sampling

Desorption techniques

Intact protein identification