Identification of an 80 kDa glycoprotein located at sites of close apposition between skeletal muscle cells.

An 80 kDa glycoprotein was isolated from adult frog skeletal muscle by concanavalin (Con A) affinity chromatography and electrophoretic separation by molecular mass. Characteristics of the 80 kDa glycoprotein are that it: 1) binds non-covalently to gelatin-agarose or some other protein(s) bound to gelatin-agarose, 2) does not bind wheat germ agglutinin, 3) appears only at 80 kDa in both reducing and non-reducing electrophoretic separations, 4) is present in skeletal muscle but absent in smooth muscle and cardiac muscle, 5) is not collagenase or hyaluronidase-sensitive, and 6) is antigenically similar to a protein in embryonic chicken skeletal muscle. It was used to generate a polyclonal antiserum which was affinity-purified and used for immunolocalization. Indirect immunofluorescence procedures showed the antigen to be present on the surface of the skeletal muscle cells and concentrated at sites where cells are closely apposed to one another. Preparations in which adult muscle cells were depleted of basement membrane and endomysial proteins did not reduce the amount of 80 kDa protein present in skeletal muscle. These data indicate that this is a cell surface glycoprotein that may mediate attachment of the cell to extracellular proteins at sites where adjacent skeletal muscle cells are apposed.