Controlled proteolysis of tubulin by subtilisin: localization of the site for MAP2 interaction

Abstract

The treatment of [pig brain] tubulin with subtilisin resulted in a significant decrease in the ability of tubulin to assemble. The addition of taxol reduced the efect of subtilisin on the assembly of digested protein. Limited proteolysis of tubulin by subtilisin affected simultaneously both .alpha.- and .beta.-subunits, and it resulted in the appearance of 2 major cleavage fragments (32 and 20 kilodaltons) or an alternative pattern yielding 2 fragments (48 and 4 kilodaltons). The smallest peptide (4 kilodaltons) and also the 20-kilodalton fragment are localized in the C-terminal region of the tubulin .alpha.-subunit. Digested tubulin can assemble into sheet-shaped polymers, which cannot incorporate MAP2 [microtubule-associated protein]. The isolated C-terminal fragments can bind to MAP2. The carboxyl-terminal domain of the tubulin molecule is probably the site for the MAP2 interaction.