Identification of proteolytic cleavage sites by quantitative proteomics

Area of Science:

• Proteomics
• Biochemistry
• Molecular Biology

Background:

• Identifying natural substrates and cleavage sites is crucial for understanding proteolytic pathways.
• Existing methods may lack sensitivity or specificity in complex biological samples.

Purpose of the Study:

• To develop a novel quantitative proteomics strategy for identifying proteolytic cleavage sites and substrates.
• To validate the new method using caspase-3 and demonstrate its sensitivity in complex biological matrices.

Main Methods:

• Proteins are guanidinated to block lysine residues, allowing N-terminal labeling with amine-specific isobaric tag for relative and absolute quantitation (iTRAQ) reagents.
• Peptides are digested, analyzed by MALDI-TOF/TOF mass spectrometry, and iTRAQ-labeled neoepitopes are identified by signature ions.
• A specific data acquisition strategy was developed for analyzing iTRAQ-tagged N-terminal peptides.

Main Results:

• The method successfully identified 10 caspase-3 cleavage sites in recombinant E. coli proteins.
• High sensitivity was demonstrated by detecting spiked caspase-cleaved substrates in human cell lysates.
• Proteolytic cleavage products were identified during cell-free apoptosis induction.

Conclusions:

• This novel application of iTRAQ technology provides a sensitive and specific approach for detecting proteolytic cleavage events and identifying substrates.
• The method advances the study of proteolytic pathways and has potential applications in biomarker discovery and disease research.