The appendage domain of alpha-adaptin is a high affinity binding site for dynamin.

Dynamin is a GTPase that appears to be required for endocytosis. Even though this molecule is known to be in surface-coated pits, the identity of the resident coat proteins that account for this localization is not known. Here we show that dynamin is one of three synaptic terminal proteins that bind with specificity to the appendage domain of alpha-adaptin. Binding is sensitive to both salt and pH levels but is not affected by nucleotides. Using recombinant dynamin expressed in SF9 cells, we estimate that the binding affinity is approximately 200 nM. Binding does not require GTP, and the GTPase activity of dynamin is not stimulated by this interaction. These results suggest that the COOH terminus of alpha-adaptin may be a domain within AP2 that mediates the initial interactions between dynamin and surface-coated pits. This may be an essential step in the regulation of coated pit budding.