A continuous fluorimetric assay for tumor necrosis factor-alpha converting enzyme

Area of Science:

• Biochemistry
• Enzymology
• Drug Discovery

Background:

• Fluorogenic peptide substrates are crucial for protease activity monitoring.
• Screening small-molecule libraries requires robust assays for protease inhibitors.

Purpose of the Study:

• To identify and characterize a novel fluorogenic substrate for tumor necrosis factor-alpha converting enzyme (TACE).
• To validate a fluorimetric assay for TACE activity.
• To investigate the kinetic properties and substrate specificity of TACE.

Main Methods:

• Design and synthesis of a capped fluorogenic peptide substrate (LAQAVRSSSR).
• Enzymatic cleavage assays monitored by fluorescence enhancement.
• High-performance liquid chromatography (HPLC) for assay validation.
• Kinetic analysis (kcat, S0.5, Hill coefficient) and substrate specificity studies.

Main Results:

• A 10-amino-acid peptide substrate with specific N- and C-terminal capping groups showed an 11-fold fluorescence enhancement upon cleavage at the A-V bond.
• The fluorimetric assay was validated by HPLC.
• Substrate hydrolysis exhibited positive cooperativity (Hill coefficient = 1.5), unlike the uncapped peptide (Michaelis-Menten kinetics).
• The capped substrate demonstrated enhanced catalytic efficiency (kcat = 21.6 s⁻¹, S0.5 = 342 μM) and a 64-fold increase in kcat due to capping.
• TACE showed a preference for the A-V scissile bond but also efficiently cleaved F-V, A-I, and A-L bonds.

Conclusions:

• A novel, highly sensitive fluorogenic substrate for TACE activity has been developed.
• The capped substrate facilitates efficient and accurate TACE activity monitoring.
• The study provides insights into TACE substrate specificity and catalytic mechanisms, including positive cooperativity.