THE ADHESION MOLECULE ON GLIA (AMOG) IS A HOMOLOG OF THE BETA-SUBUNIT OF THE NA,K-ATPASE

AMOG (adhesion molecule on glia) is a Ca2+-independent adhesion molecule which mediates selective neuron-astrocyte interaction in vitro (Antonicek, H., E. Persohn, and M. Schachner. 1987. J. Cell Biol. 104:1587-1595). Here we report the structure of AMOG and its association with the Na,K-ATPase. The complete cDNA sequence of mouse AMOG revealed 40% amino acid identity with the previously cloned β subunit of rat brain Na,K-ATPase. Immunoaffinity-purified AMOG and the β subunit of detergent-purified brain Na,K-ATPase had identical apparent molecular weights, and were immunologically cross-reactive. Immunoaffinity-purified AMOG was associated with a protein of 100,000 M(r). Monoclonal antibodies revealed that this associated protein comprised the α2 (and possibly α3) isoforms of the Na,K-ATPase catalytic subunit, but not α1. The monoclonal AMOG antibody that blocks adhesion was shown to interact with Na,K-ATPase in intact cultured astrocytes by its ability to increase ouabain-inhibited 86Rb+ uptake. AMOG-mediated adhesion occurred, however, both at 4°C and in the presence of ouabain, an inhibitor of the Na,K-ATPase. Both AMOG and the β subunit are predicted to be extracellularly exposed glycoproteins with single transmembrane segments, quite different in structure from the Na,K-ATPase α subunit or any other ion pump. We hypothesize that AMOG or variants of the β subunit of the Na,K-ATPase, tightly associated with an α subunit, are recognition elements for adhesion that subsequently link cell adhesion with ion transport.