GTPase involved in endocytosis
Dynamin was discovered because of its binding to microtubules. It was later shown not to function in the cytoskeleton
but in endocytosis. Dynamin is required for clathrin - mediated endocytosis. It contains a NH2 - terminal GTPase domain, a
middle pleckstrin - homology domain, and a COOH- terminal proline - rich sequence. The COOH - terminal sequence binds to
amphiphilin which contains a SH3 domain that recognizes the proline -rich sequence of dynamin. There are at least three isoforms
of dynamin: Dynamin 1 is enriched in synapses whereas dynamin 2 is ubiquitous and dynamin 3 is expressed in the testis. Neuronal
dynamin 1 is phosphorylated by protein kinase C and dephosphorylated by calcineurin during an action potential in the nerve
terminal. It is possible that the dephosphorylation provides a trigger for endocytosis.
movie structure clathrin
dynamin ; What is it? a large GTPase involved in the scission of nascent vesicles from parent membranes.
How do we think it works? Dynamin forms a helix around the neck of a nascent vesicle (like in the above movie). Cooperative
GTP hydrolysis results in the lengthwise extension of this helix, breaking the vesicle neck (but see below for an overview
of other plausible mechanisms).