Conserved amphipathic helices near the N-terminus and C-terminus of the alpha subunit of cranin (dystroglycan)

Cranin (dystroglycan) is a ubiquitously expressed extracellular matrix receptor, synthesized as a single precursor, which is cleaved into an extracellular subunit (alpha) and a transmembrane subunit (beta). The primary sequence of cranin (dystroglycan) is known from cDNA cloning, and the protein has been strongly implicated in morphogenesis, cell adhesion and human disease. Nevertheless, the domain structure of the alpha subunit has not been well studied; although the protein binds to matrix proteins, to the beta subunit, to cell surfaces, and possibly to other membrane proteins such as sarcoglycans, the domains responsible for mediating these interactions remain unknown. Here I report computer analyses that identify two distinctive amphipathic alpha-helical regions near the N-terminus and C-terminus of the alpha subunit, which are conserved in all species for which sequence information is currently available. This finding should stimulate and guide experimental studies designed to understand how the alpha subunit is associated with the cell surface and with its various ligands.