ELECTRON-MICROSCOPIC EVIDENCE FOR A MUCIN-LIKE REGION IN CHICK MUSCLEALPHA-DYSTROGLYCAN

alpha-Dystroglycan has been isolated from chicken cardiac muscle and i ts molecular weight was estimated to be approximate to 135 kDa. The av ian protein interacts with murine Engelbreth-Holm-Swarm (EHS) tumor la minin via interaction with the C-terminal LG4 and LG5 domains (fragmen t E3) of the laminin alpha-chain. This laminin binding is calcium-depe ndent and can be competed by heparin. Electron microscopy investigatio n on the shape of alpha-dystroglycan suggests that the core protein co nsists of two roughly globular domains connected by a segment which mo st likely corresponds to a mucin-like central region also predicted by sequence analysis on mammalian isoforms. This segment may act as a sp acer in the dystrophin-associated glycoproteins complex exposing the N -terminal domain of alpha-dystroglycan to laminin in the extracellular space.