Dynamin is a membrane-associated GTPase that binds to GTP, microtubules, and phospholipids. Northern blot analysis has shown dynamin to be present in most tissues but at an amount about 20-fold lower than that in brain. There are at least two distinct dynamin genes in mammals. Transcripts of both dynamin genes are alternatively spliced at two or more sites. The first site is identical in both dynamins, whereas, the second site differs. The two gene products are known as Dynamin I and Dynamin II and show 79% identity. Dynamin I is expressed almost exclusively in the central nervous system while Dynamin II expression is ubiquitous. The two proteins are highly homologous in the N-terminal region, while the C-terminal domain shows significant divergence. The GTPase activity of Dynamin I is stimulated several fold by binding to microtubules, phospholipids, and membranous vesicles. Dynamin I is a good substrate of PKC in vitro as well as in vivo in resting nerve terminals. In vitro, phosphorylation occurs at the C-terminus of Dynamin I and this enhances the GTPase activity more than 10-fold. However, Dynamin II is not a substrate of PKC and its activity does not appear to be affected by phosphorylation. These data suggest that the function of the common N-terminal domain between Dynamin I and II may be differentially specified by distinct C-terminal domains.
