Molecular basis of proteolytic cleavage regulation by the extracellular matrix receptor dystroglycan

The dystrophin glycoprotein complex (DGC), anchored by the transmembrane protein dystroglycan, functions to mechanically link the extracellular matrix to the actin cytoskeleton to drive critical aspects of development and adult homeostasis. Breaking this connection via mutation of the actin adaptor protein dystrophin or impaired glycosylation of dystroglycan are strongly associated with diseases such as Muscular Dystrophy, yet cleavage of the dystroglycan protein by matrix metalloproteinases (MMPs) remains an understudied mechanism to disrupt the DGC. We solved X-ray structures of the membrane-adjacent domain of dystroglycan to understand the molecular underpinnings of dystroglycan MMP cleavage regulation. Dystroglycan proteolysis occurs within the versatile SEAL domain, which supports proteolysis in diverse receptors to facilitate mechanotransduction, protection of cell membranes, and even viral entry. The structure reveals a c-terminal extension of the SEAL domain that buries the MMP cleavage site by packing into a hydrophobic pocket, a unique mechanism of MMP cleavage regulation. We further demonstrate that structure-guided and disease-associated mutations disrupt proteolytic regulation using a new cell-surface proteolysis assay. Finally, we find that disruption of proteolysis leads to altered cellular mechanics and migration using high-throughput DNA tension probe and wound healing assays. These findings highlight that disrupted proteolysis is a relevant mechanism for breaking the DGC link to contribute to disease pathogenesis and may offer new therapeutic avenues for dystroglycanopathies. ### Competing Interest Statement The authors have declared no competing interest.