Enhancement of Tryptic Peptide Signals from Tissue Sections Using MALDI IMS Postionization (MALDI-2)

Area of Science:

• Proteomics
• Analytical Chemistry
• Biotechnology

Background:

• Matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI IMS) enables multiplexed, unlabeled analyte mapping in tissues.
• Current limitations exist in sensitivity and depth of coverage for protein and peptide IMS.

Purpose of the Study:

• To improve sensitivity and depth of coverage for protein and peptide IMS.
• To demonstrate signal enhancement using a dual-laser approach (MALDI-2) for proteolytic peptides in human kidney tissue.

Main Methods:

• Proteins in thin human kidney tissue sections were digested in situ with trypsin.
• Conventional MALDI (MALDI-1) was augmented with a second ionizing laser (MALDI-2).
• Peptide and protein identification was performed using LC-MS/MS on tissue homogenate and matched to MALDI IMS data via in silico digestion.

Main Results:

• MALDI-2 resulted in a significant increase in identified unique peptides (2076 ± 362) compared to MALDI-1 (1337 ± 96).
• Protein identifications (requiring ≥2 peptides) increased from 276 ± 20 with MALDI-1 to 401 ± 60 with MALDI-2.
• MALDI-2 demonstrated enhanced sensitivity for spatial mapping of tryptic peptides.

Conclusions:

• MALDI-2 significantly enhances sensitivity for peptide and protein identification in MALDI IMS.
• The dual-laser approach substantially increases the number of proteins that can be identified and spatially mapped in tissue sections.