Phosphatidylserine exposure is required for ADAM17 sheddase function

Area of Science:

• Biochemistry
• Cell Biology
• Molecular Biology

Background:

• ADAM17 (A Disintegrin and Metalloproteinase domain) is a key enzyme regulating cellular processes by cleaving transmembrane proteins.
• The precise mechanisms controlling ADAM17's sheddase activity and substrate targeting remain incompletely understood.

Purpose of the Study:

• To investigate the role of phosphatidylserine (PS) exposure in mediating ADAM17 sheddase activity.
• To identify the molecular interactions between ADAM17 and PS that facilitate substrate cleavage.

Main Methods:

• Utilized apoptosis-induced Raji cells, PS-manipulatable PSA-3 cells, and Scott syndrome lymphocytes lacking PS externalization.
• Employed soluble phosphorylserine and phosphorylcholine as inhibitors.
• Characterized the binding of the ADAM17 membrane proximal domain (MPD) to PS and phosphatidylcholine liposomes.
• Identified and mutated a cationic PS-binding motif within the ADAM17 MPD.

Main Results:

• PS exposure was tightly correlated with substrate shedding induced by various ADAM17 activators.
• Soluble PS, but not phosphorylcholine, inhibited ADAM17-mediated substrate cleavage.
• The isolated ADAM17 MPD specifically bound to PS liposomes.
• Mutation of a cationic PS-binding motif in the MPD abolished liposome binding and cellular substrate cleavage.

Conclusions:

• Surface exposure of phosphatidylserine is essential for ADAM17 to perform its sheddase function.
• A specific PS-binding motif within the ADAM17 MPD is critical for protease localization and activity.
• These findings suggest that PS acts as a docking site, directing ADAM17 to its substrates for cleavage.