Proteolytic cleavage of high-molecular-weight microtubule-associated proteins by the prostatic estramustine-binding...

The rat prostatic estramustine-binding protein was found to inhibit assembly of microtubules in a concentration-dependent manner. The inhibition was caused by a proteolytic cleavage of the high-molecular-weight microtubule associated proteins (MAPs), as judged by sodium dodecyl sulfate-gel electrophoresis. A proteolytic fragment with a molecular weight of 199 kDa appeared, which remained bound to the assembled microtubules. Fragments of lower molecular weights (170, 149 kDa) were also found, but they did not bind to the assembled microtubules. Fragments with identical molecular weights were also found after incubation of purified MAP2 with the estramustine-binding protein, indicating that the fragments derive from MAP2. No proteolysis of tubulin, albumin, or casein was found. The estramustine-binding protein was found to be a Zn2+-dependent protease; it was inhibited by EDTA and reactivated by addition of 1 mM Zn2+. Its proteolytic activity was not affected by binding of the antimitotic drug estramustine.