Improved Detection of Tryptic Peptides from Tissue Sections Using Desorption Electrospray Ionization Mass...

Area of Science:

• Mass Spectrometry Imaging
• Proteomics
• Biochemistry

Background:

• Desorption Electrospray Ionization Mass Spectrometry Imaging (DESI-MSI) is typically used for small molecules, with limited protein and peptide detection.
• Previous DESI-MSI studies faced challenges in data deconvolution, limiting the number and spatial resolution of detected species.
• Differences in ion detection between DESI-MSI and Matrix-Assisted Laser Desorption/Ionization (MALDI) for non-peptide molecules are known and extend to proteomic species.

Purpose of the Study:

• To evaluate the potential of DESI-MSI for enhanced detection and spatial localization of tryptic peptides in tissue sections.
• To investigate the impact of ion mobility separation on resolving spectral overlap and improving multiply charged peptide detection.
• To compare the spatial localization of peptide ions detected by DESI-MSI and MALDI.

Main Methods:

• Tissue sections of mouse and rat brain were analyzed using DESI-MSI with a heated inlet (approx. 450 °C).
• Ion mobility separation was employed to resolve spectral overlap and enhance detection of multiply charged peptide ions.
• Tryptic peptides were identified and spatially mapped at 50 μm (mouse brain) and 100 μm (rat brain) pixel sizes, with tentative protein assignment via LC-MS data.

Main Results:

• DESI-MSI successfully detected a larger number of tryptic peptides from tissue sections with improved spatial resolution compared to prior studies.
• Ion mobility separation significantly improved the detection of multiply charged peptide species and resolved spectral overlap.
• Spatial localization of peptide ions by DESI-MSI was comparable to MALDI, with some unique detections by DESI-MSI, particularly low m/z multiply charged species.

Conclusions:

• DESI-MSI, enhanced with ion mobility separation and a heated inlet, demonstrates significant potential for high-resolution proteomic analysis directly from tissue.
• This refined DESI-MSI approach expands its utility to the detection of a broader range of proteomic species, including multiply charged peptides.
• The technique offers comparable spatial localization to MALDI while potentially detecting species missed by other methods, paving the way for advanced spatial proteomics.