Regulation of microtubule cold stability by calmodulin-dependent and -independent phosphorylation.

Publisher Website
Google Scholar
Abstract
Cold-labile [beef brain] microtubule protein can be rendered cold-stable by addition of a fraction containing a small number of polypeptides that are derived from cold-stable microtubules. These polypeptides can be obtained from purified cold-stable microtubules by passage through a DEAE-cellulose (DE-52) ion exchange column from which they emerge in the 1st eluate fraction. The stabilizing actiivty of these proteins is abolished by phosphorylation catalyzed by 2 types of protein kinases, one dependent on calmodulin and the other independent of that regulatory protein. The calmodulin-dependent reaction appears to phosphorylate mainly 2 polypeptides, 56 and 72 kilodaltons; the reaction is blocked by trifluoperazine. The calmodulin-independent reaction appears to phosphorylate different cold-stable microtubule-associated proteins. That reaction is observed only in purified material obtained from vigorously homogenized brain tissue. Gentle homogenization yields cold-stable microtubules that are responsive only to the calmodulin-dependent protein kinase. A distinguishing feature of the calmodulin-independnt reaction is that it does not occur on polypeptides while they are bound to the microtubules.