Relative protein quantification by isobaric SILAC with immonium ion splitting (ISIS)

Area of Science:

• Proteomics
• Mass Spectrometry
• Biochemistry

Background:

• Metabolic labeling techniques, such as stable isotope labeling with amino acids in cell cultures (SILAC), are crucial for quantitative proteome profiling.
• Classical SILAC relies on predictable mass differences introduced by heavy/light isotopic amino acids for relative protein quantification via mass spectrometry.
• Existing methods require distinct mass shifts for peptide correlation and quantification.

Purpose of the Study:

• To present an alternative SILAC approach utilizing isobaric labeling with distinct isotopic labels (13C or 15N) for relative protein quantification.
• To validate the efficacy and sensitivity of this novel isobaric SILAC method for proteome analysis.
• To compare the performance of isobaric SILAC with established techniques like 2D DIGE.

Main Methods:

• Culturing cells in media with isobaric amino acid forms labeled with 13C or 15N.
• Generating distinct immonium ions (separated by 1 amu) upon fragmentation of labeled peptides from mixed samples.
• Utilizing immonium ion intensities for relative protein quantification and employing a fast scan event for enhanced sensitivity.

Main Results:

• Achieved high labeling coverage (97%) for tryptic peptides using valine, isoleucine, and leucine.
• Demonstrated reliable quantification of protein mixtures with known ratios.
• Obtained quantitative data from melanoma cell lines consistent with 2D DIGE analysis.

Conclusions:

• The developed isobaric SILAC method effectively quantifies proteins by leveraging distinct immonium ion fragmentation patterns.
• This approach combines SILAC's features with the benefits of isobaric labeling schemes, enhancing sensitivity and quantification accuracy.
• The method shows promise for proteomic studies, offering a valuable alternative for quantitative analysis.