Tuba, a GEF for CDC42, links dynamin to actin regulatory proteins.

Tuba is a 178kD protein containing four NH2-terminal SH3 domains, a central Dbl homology (DH) domain followed by a BAR domain, and two COOH-terminal SH3 domains. The four NH2-terminal SH3 domains bind the GTPase dynamin, a protein critical for the fission of endocytic vesicles. The DH domain functions as a CDC42-specific guanine nucleotide exchange factor and is unique among DH domains because it is followed by a BAR domain rather than a PH domain. The COOH-terminal SH3 domain binds directly to N-WASP and Ena/VASP proteins, key regulatory proteins of the actin cytoskeleton, and recruits a larger protein complex comprising additional actin regulatory factors. The properties of Tuba provide new evidence for a functional link between dynamin, endocytosis, and actin. The presence of a BAR domain, rather than a PH domain, may reflect its action at high curvature regions of the plasma membrane. Its multiple binding sites for dynamin generate an exceptionally high avidity for this GTPase and make the NH2-terminal region of Tuba a very useful tool for the one-step purification of dynamin.