The 93-kDa glycine receptor-associated protein binds to tubulin

A peripheral membrane protein with a relative molecular mass of 93,000 Da is associated with cytoplasmic domains of the inhibitory glycine receptor of mammalian spinal cord. Here, evidence is given that this 93-kDa protein binds to polymerized tubulin. First, tubulin cofractionated with the 93-kDa protein upon affinity purification of the glycine receptor. Second, tubulin bound to the isolated 93-kDa protein in an overlay procedure. Third, in assays containing the purified glycine receptor, the 93-kDa protein as well as the glycine receptor α and β subunits coassembled with tubulin and microtubules. The interaction of the 93-kDa protein with tubulin displayed high affinity (K_D ap; 2.5 nM) and significant cooperativity (Hill coefficient ≈ 2.1) and approached a stoichiometry of ∼1:4 under saturating conditions. These data suggest that the 93-kDa protein anchors the glycine receptor at postsynaptic sites via binding to subsynaptic tubulin.