# Integrated Native Mass Spectrometry Imaging of Soluble and Membrane Proteins

## TL;DR

A new method allows simultaneous analysis of soluble and membrane proteins in tissue using mass spectrometry imaging, without special preparation.

## Contribution

A new nano-DESI mode enables combined analysis of soluble and membrane proteins in one experiment using a single tissue section.

## Key findings

- Elution profiles separate soluble and membrane protein signals during nano-DESI.
- The method works on kidney and brain tissues with quick data acquisition.
- Signal-to-noise improvements are achieved for imaging and mass spectrometry workflows.

## Abstract

Native ambient mass spectrometry enables the analysis
of intact
protein complexes directly from fresh frozen tissue sections together
with visualization of their spatial distribution as part of a mass
spectrometry imaging workflow. Native mass spectrometry imaging typically
employs nanospray-desorption electrospray ionization (nano-DESI),
a liquid junction sampling approach. Imaging of both soluble and membrane
proteins has been demonstrated by native nano-DESI but, crucially,
imaging of one protein type has always been at the expense of the
other, requiring tailored sample preparation and multiple tissue sections.
Here, we introduce a new mode of nano-DESI operation that combines
soluble and membrane protein analysis into a single experiment, requiring
no sample preparation and only a single tissue section, and which
is compatible with mass spectrometry imaging. Chromatography-like
separation of soluble and membrane protein signals, observed as varying
elution profiles, occurs when the nano-DESI probe is parked in a fixed
location on the tissue. The elution profiles of proteins in both kidney
and brain tissue were explored. The results show that elution profiles
are quick to record, offer insight into the classification of unknown
proteins detected from tissue and enable signal-to-noise improvements
to imaging and native top-down mass spectrometry workflows.