Native nano-DESI images intact kidney proteins
Ammonium-acetate nano-DESI mass spectrometry imaging maps folded proteins and a noncovalent S100-A6 dimer in rat kidney at finer spatial scale than LESA.
Source
Native Mass Spectrometry Imaging of Proteins and Protein Complexes by Nano-DESI
Study at a glance
- Design
- Animal / in-vitro — Native nano-DESI MS imaging of proteins/complexes on rat kidney sections
- N
- 10 μm rat kidney sections; imaging method development — no cohort N
- Population
- Rat kidney tissue sections and protein standards
- Outcome
- Spatial detection of native proteins and noncovalent complexes
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What they did
The authors built a custom nano-DESI source on an Orbitrap Eclipse and sampled protein standards plus 10 μm rat kidney sections from ammonium acetate with a small amount of C8E4 detergent. They acquired ion images at 20 μm/s with 200 μm line spacing, then used location-targeted tandem MS and proton-transfer charge reduction to identify native proteins in situ.
What they found
Native nano-DESI resolved kidney anatomy more finely than prior LESA imaging (typical LESA spots ~600 μm). They identified proteins not seen by native LESA, including the noncovalent S100-A6 homodimer, ALBP, and PEBP1. The largest species detected was the RidA trimer at 42.6 kDa. Images took about 7 h per section.
The limits
What it doesn't show
The work is method development on one rat kidney, not a biological hypothesis test. Protein signals are weak versus lipids, so higher spatial resolution would likely cost intensity. PTCR and oversampling were not fully validated as native-protein imaging strategies.
Key terms
- Native mass spectrometry
- MS of proteins from near-physiological solutions so noncovalent structure and complexes can survive into the gas phase.
- nano-DESI
- Nanospray desorption electrospray ionization: a liquid junction continuously samples a surface into a mass spectrometer.
- Mass spectrometry imaging
- Spatially resolved MS that maps molecular ions across a tissue or surface.
- LESA
- Liquid extraction surface analysis, an earlier droplet-based ambient sampling method with coarser spatial resolution.
- PTCR
- Proton-transfer charge reduction, used here to simplify overlapping protein charge-state envelopes.
Flashcards
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Common questions
Why use ammonium acetate instead of organic/acid solvents?
Nondenaturing aqueous ammonium acetate keeps proteins folded so native charge states and complexes can be observed.
What complex was newly identified in kidney?
The noncovalent homodimer of S100-A6, plus ALBP and PEBP1 that LESA had missed.
What limited earlier native MSI?
LESA sampling spots of about 600 μm diameter and 1 mm pixels, too coarse for fine tissue features.
What is the heaviest native assembly reported?
The RidA trimer at 42.6 kDa.
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