The interaction between a Na+-channel toxin and brain microtubule proteins in vitro

The aim of this work was to characterize the interaction of the Na+-channel toxin, purified from venom of the scorpion Leiurus quinquestriatus, with microtubule proteins in vitro. The toxin enhanced microtubule assembly, causing the formation of microtubule 'bundles'. It interacted with the Na+-channel 270 kDa subunit and was subsequently found to be unrelated to high molecular weight microtubule-associated protein with respect to apparent molecular weight and toxin binding. However, the radiolabelled toxin bound to tubulin, although with a much lower affinity than that published for the reconstituted Na+-channel. This binding appears to occur in the carboxy terminal 4 kDa region of tubulin. These results may reflect a secondary action of the toxin involved in binding to its receptors in the neural plasma membrane.