Matrix-assisted ionization mass spectrometry in targeted protein analysis - An initial evaluation

Area of Science:

• Analytical Chemistry
• Biochemistry
• Mass Spectrometry

Background:

• Matrix-assisted ionization (MAI) is an emerging ionization technique for mass spectrometry (MS).
• MAI exhibits reduced matrix effects compared to electrospray ionization (ESI).
• These characteristics make MAI suitable for targeted protein analysis in biological samples.

Purpose of the Study:

• To evaluate matrix-assisted ionization coupled with selected reaction monitoring mass spectrometry (MAI-SRM-MS) for targeted protein quantification.
• To assess the applicability of MAI-SRM-MS using a bottom-up proteomic approach with stable isotopic labeled peptides as internal standards.
• To investigate the performance of MAI-SRM-MS in complex biological matrices.

Main Methods:

• Utilized a triple quadrupole mass analyzer with a nanoESI source in selected reaction monitoring (SRM) mode.
• Employed the bottom-up proteomic strategy with stable isotopic labeled peptides as internal standards (IS).
• MAI matrix consisted of 3-nitrobenzonitrile in acetonitrile, mixed with aqueous samples at a 1:3 ratio.

Main Results:

• Established SRM settings for electrospray ionization (ESI-SRM-MS) were transferable to MAI-SRM-MS for most peptides.
• Internal standards effectively corrected quantification across various digest levels (RSD ≤28%) and in complex matrices like diluted urine and serum.
• Sufficient dilution was necessary to mitigate signal suppression from biological matrices.

Conclusions:

• MAI-SRM-MS demonstrates significant potential for simple, rapid, and user-friendly targeted protein determination via the bottom-up approach.
• Further validation is required before clinical implementation of MAI-SRM-MS.
• The technique's robustness in handling biological samples warrants continued investigation.