Using a bioluminescence resonance energy transfer caspase biosensor to study caspase-3 cleavage site specificity

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Apoptosis involves a caspase cascade, with caspase-3 central to the process.
• Existing assays for caspase-3 activity often use peptides, limiting protein substrate insights.
• Understanding caspase-3 substrate specificity is crucial for studying apoptosis.

Purpose of the Study:

• To develop and validate a novel protein-based biosensor for quantitative kinetic measurements of caspase-3 activity.
• To systematically determine the catalytic specificity of caspase-3 for different amino acids at the P4 position of its substrates.
• To assess the utility of the biosensor in live apoptotic cells.

Main Methods:

• Development of a recombinant protein-based double brilliance bioluminescence resonance energy transfer (BRET2) biosensor assay.
• Systematic evaluation of caspase-3 cleavage-site motif preferences using BRET2 biosensors with variations at the P4 position.
• Kinetic analysis (kcat/KM) of caspase-3 activity.
• Validation of the biosensor in apoptotic cells.

Main Results:

• The BRET2 biosensor assay provides robust and quantitative kinetic measurements of caspase-3 activity in vitro.
• Catalytic specificity (kcat/KM) for caspase-3 was determined for 18 out of 20 amino acids at the P4 position.
• The range of proteolytic efficacies observed was narrower than previously reported with peptide-based libraries.
• The biosensor demonstrated utility and robustness in live apoptotic cells.

Conclusions:

• The novel protein-based BRET2 biosensor is a valuable tool for studying caspase-3 kinetics and substrate specificity.
• This assay offers a more biologically relevant approach compared to traditional peptide-based methods.
• The biosensor's applicability in cellular contexts highlights its potential for apoptosis research.