The Interactions between Calcium-Dependent Regulator Protein of Cyclic Nucleotide Phosphodiesterase and Microtubule Proteins I. Effect of Calcium-Dependent Regulator Protein on the Calcium Sensitivity of Microtubule Assembly

Abstract

We examined the effect of porcine brain Ca²⁺ -depenent regulator (CDR) protein on microtubule (MT) assembly from microtubular proteins isolated from porcine brain by temperature- dependent cycles of assembly-disassembly. CDR exhibited a potent inhibitory effect on MT assembly in the presence of Ca whereas it had little or no effect on the extent of MT assembly in the absence of Ca²⁺ The increase in KCl concentration greatly potentiated the Ca²⁺ dependent inhibitory effect of CDR. The effect of CDR was reversible in a Ca²⁺ concentration-dependent manner, and the extent of inhibition by CDR at a fixed concentration of free Ca was roughly proportional to the concentration of CDR. Moreover, the Ca con centration required for the half-maximal inhibition of MT assembly from a fixed concentration of purified rnicrotubular proteins (PMP) decreased with increasing CDR concentration. On the basis of these results, together with data on the Ca association of CDR and tubulin (J. Biochem., accompanying paper), we propose the following model; Ca²⁺+CDR ⇌ Ca²⁺−CDR Ca²⁺−CDR+tubulin ⇌ Ca²⁺−CDR−tubulin (nonpolymerizable)