Characterization of the transmembrane molecular architecture of the dystroglycan complex in Schwann cells

We have demonstrated previously 1) that the dystroglycan complex, but not t he sarcoglycan complex, is expressed in peripheral nerve, and 2) that alpha -dystroglycan is an extracellular laminin-a-binding protein anchored to bet a-dystroglycan in the Schwann cell membrane. In the present study, we inves tigated the transmembrane molecular architecture of the dystroglycan comple x in Schwann cells. The cytoplasmic domain of beta-dystroglycan was co-loca lized with Dp116, the Schwann cell-specific isoform of dystrophin, in the a baxonal Schwann cell cytoplasm adjacent to the outer membrane, beta-dystrog lycan bound to Dp116 mainly via the 15 C-terminal amino acids of its cytopl asmic domain, but these amino acids were not solely responsible for the int eraction of these two proteins. Interestingly, the beta-dystroglycan-precip itating antibody precipitated only a small fraction of alpha-dystroglycan a nd did not precipitate laminin and Dp116 from the peripheral nerve extracts . Our results indicate 1) that Dp116 is a component of the submembranous cy toskeletal system that anchors the dystroglycan complex in Schwann cells, a nd 2) that the dystroglycan complex in Schwann cells is fragile compared wi th that in striated muscle cells. We propose that this fragility may be att ributable to the absence of the sarcoglycan complex in Schwann cells.