Structure and function of a Notch-like proteolytic switch domain in the extracellular matrix receptor dystroglycan

Abstract

AbstractThe adhesion receptor dystroglycan provides a critical mechanical link between the extracellular matrix (ECM) and the actin cytoskeleton to help muscle cells withstand contraction and neural cells maintain the blood brain barrier. Disrupting the link is associated cancer and muscular dystrophy. Proteolysis of dystroglycan by matrix metalloproteinases (MMPs) provides a mechanism to break the mechanical anchor and is amplified in several pathogenic states, yet how MMP cleavage is regulated is largely unexplored. We solved the crystal structure of the extracellular membrane-adjacent domains of dystroglycan containing the MMP site and find the tandem Ig-like and SEA-like domains structurally interact in an L-shape to facilitate a permissive conformation for α/β auto-catalytic processing. The MMP cleavage site is located in a structural motif C-terminal to the SEA-like domain that folds back and nestles into a pocket within the SEA-like domain to protect the cleavage site from MMPs. We then show while the intact proteolytic switch domain is resistant to MMP cleavage, structurally disruptive muscular dystrophy-related mutations sensitize dystroglycan to proteolysis in secreted constructs and the full-length receptor. Intriguingly, previously uncharacterized cancer-associated mutations that map to the proteolytic switch domain similarly lead to increases in proteolysis. Taken together, this study demonstrates dystroglycan proteolysis is conformationally regulated and mutations in the domain lead to enhanced proteolysis.