GLYCOLIPID-PROTEIN INTERACTION IN THE MECHANISM OF SIGNAL-TRANSDUCTION - STUDIES WITH A PHOTOACTIVABLE GANGLIOSIDE ANALOG

An increasing body of evidence suggests that glycolipid domains are pr esent on the plasma membrane surface of mammalian cells and play a key role in signal transduction. We have investigated the modulation of g lycolipid-protein interaction consequent to a specific event occurring at the plasma membrane. For this purpose, a new photoactivable, radio active derivative of G(M1) ganglioside, carrying a phenyldiazirine fat ty acid labelled with I-125, has been used with rat cerebellar granule cells in culture. Upon incubation of photoactivable G(M1) with the ce lls followed by illumination, several proteins become radioactive and mere detectable on the two dimensional-electrophoresis, which points t o their interaction with the ganglioside. Upon addition of cytotoxic d oses of glutamate, known to induce indirectly the activation of protei n kinase C (PKC), one of the proteins crosslinked by photoactivable G( M1) in control cells of molecular mass about 92 kDa and pI about 4, wa s not anymore detectable; this suggests its exclusion from the glycoli pid domains. On the contrary, another protein, of about 15 kDa and pI 6.5, previously not crosslinked, was interacting with the ganglioside derivative after glutamate treatment. Comparable effects were exerted by phorbol-2-myristate-3-acetate, which directly induces the activatio n of PKC. These results show that PKC activation, a key step of inboun d trans-membrane signalling, affects the interaction between glycolipi ds and proteins at the plasma membrane surface, possibly within a mixe d domain. The dynamic modulation of ganglioside-protein interaction ma y affect the involvement of glycolipid domains in membrane-located eve nts such as signal transmission and lipid/protein sorting.