Ganglioside-binding proteins in skeletal and cardiac muscle

Several ganglioside-binding proteins have been identified in guinea pig skeletal and cardiac muscle. In the cytosolic fractions of both tissues, a 130-kD protein was found to have the highest propensity to bind lucifer yellow CH-labelled GM1. This binding could be abolished by prior incubation of the protein with GM2. Polysialogangliosides including GD1a, GD1b, GT1b, and GQ1b were less effective. The 130-kD protein migrated as a doublet with apparent isoelectric points (pI) of 6.3 and 6.5, respectively, in isoelectric focusing gel, but as a single species with an apparent Mr of 43,000 in SDS-polyacrylamide gel. Both the ganglioside-binding and the immunological properties of the 43-kD subunit protein were different from those of rabbit skeletal muscle actin. Cardiac muscle extract also contained a 77-kD minor ganglioside-binding protein that was absent in skeletal muscle. This protein had an apparent pI of 5.4 and migrated as a 39-kD species in SDS gels. By contrast, only the particulate fraction of skeletal muscle was found to contain a 180-kD major ganglioside-binding protein. Binding of fluorescent GM1 to this protein was blocked by pre-incubation of the protein with GM1 or GM2. The 180-kD protein migrated as a 98-kD species in SDS gels. However, its propensity to bind lucifer yellow CH-GM1 was at least 10 times greater than that of rabbit skeletal muscle phosphorylase b (Mr = 97,400). The apparent pI (6.5) of the 180-kD protein also was slightly higher than that of rabbit phosphorylase. Tissue distribution studies revealed that both the 130-kD and the 180-kD major ganglioside-binding proteins were muscle specific. It is, therefore, possible that these two proteins may play some unique roles in ganglioside-related functions in muscle tissues.