Correlation between self-association modes and GTPase activation of dynamin

The GTPase activity of dynamin is obligatorily coupled, by a mechanism yet unknown, to the internalization of clathrin-coated endocytic vesicles. Dyna min oligomerizes in vitro and in vivo and both its mechanical and enzymatic activities appear to be mediated by this self-assembly. In this study we d emonstrate that dynamin is characterized by a tetramer/monomer equilibrium with an equilibrium constant of 1.67 x 10(17) M-3. Stopped-flow fluorescenc e experiments show that the association rate constant for 2'(3')-O-N-methyl anthraniloyl (mant)GTP is 7.0 x 10(-5) M-1 s(-1) and the dissociation rate constant is 2.1 s(-1), whereas the dissociation rate constant for mantdeoxy GDP is 93 s(-1). We also demonstrate the cooperativity of dynamin binding a nd GTPase activation on a microtubule lattice. Our results indicate that dy namin self-association is not a sufficient condition for the expression of maximal GTPase activity, which suggests that dynamin molecules must be in t he proper conformation or orientation if they are to form an active oligome r.