Microtubule-associated protein autophosphorylation alters in vitro microtubule dynamic instability

Abstract

While phosphorylation of high-molecular-weight microtubule-associated proteins (MAPs) alters the assembly properties of microtubules in vitro, virtually nothing is known about the influence of MAP phosphorylation on the time-scale of microtubule polymer length redistribution, The latter has been used as an index of microtubule assembly/disassembly turnover as predicted by the dynamic instability model (Mitchison, T.M. and Kirschner, M.W. (1984) Nature 312, 237–242). We have now determined that under conditions leading to the incorporation of 8–10 mol phosphoryl groups per mol MAP-2 (and about 0.2 mol phosphoryl groups per mol MAP-1 and tau), we can reproducibly observe significant acceleration in the polymer length redistribution process in a manner consistent will greater microtubule dynamic instability. We have also found that MAP phosphorylation resulted in more extensive release of MAPs from microtubules as a function of increasing salt concentration. These results are consistent with a weakening of MAP-microtubule interactions upon phosphorylation