Assessing the role of the ±/²-dystroglycan interface for the processing and maturation of the dystroglycan precursor

Dystroglycan (DG) is a receptor for several extracellular matrix proteins, including laminin, perlecan and agrin, that provides structural stability to the plasma membrane [1]. In skeletal muscle cells, DG is the central component of the dystrophin-glycoprotein-complex (DGC), a group of peripheral and membrane proteins that connects the extracellular matrix to dystrophin. Mutations in any of the DGC components are linked to distinct forms of muscular dystrophies characterized by disassembling of the whole complex followed by degeneration of muscle fibers [2]. DG is formed by two subunits, alpha and beta: _-DG is a highly glycosylated peripheral membrane protein that binds extracellular molecules while _-DG is a transmembrane protein whose cytosolic domain interacts with dystrophin linking DG to the actin cytoskeleton. The two DG subunits arise from a post-translational cleavage of a single DG precursor and remain associated via a non-covalent interaction. The molecular details of DG processing are still largely unknown. Recently, we showed that the correct formation of the _/_-DG interface is likely to stabilize the precursor and it is essential for its cleavage. Moreover, mutations hitting the _/_-DG binding epitopes inhibit the membrane targeting of mutant proteins that are retained in subcellular compartments [3]. At this stage, we widened the analysis of DG processing and maturation with the help of confocal microscopy to determine how single and multiple missense mutations located at the _/_-DG interface affect the assembly, targeting and function of the entire DG complex. We also analyzed the processing of wild-type and mutant DG precursors in the presence of different inhibitors of protein trafficking and glycosylation. In addition, a novel targeting vector for introducing multiple mutations of the _/_ interface in transgenic mice has been produced and it is currently used for preparing knock-in mice.Although no natural mutations are associated to the DG gene, a finest biochemical analysis of DG processing and maturation might be helpful to give new insights into congenital muscular dystrophies characterized by secondary defects of the _-DG glycosylation. References1. Ibraghimov-Beskrovnaya O., et al. (1992) Nature 355, 696-702.2.Barresi R. and Campbell K.P. (2006) J. Cell. Sci. 119, 199-207.3. Sciandra F. et al. (2009) FEBS J., 276, 4933-4945.