Amphiphysin I and regulation of synaptic vesicle endocytosis.

Amphiphysin I, known as a major dynamin-binding partner localized on the collars of nascent vesicles, plays a key role in clathrin-mediated endocytosis (CME) of synaptic vesicles. Amphiphysin I mediates the invagination and fission steps of synaptic vesicles by sensing or facilitating membrane curvature and stimulating the GTPase activity of dynamin. Amphiphysin I may form a homodimer by itself or a heterodimer with amphiphysin II in vivo. Both amphiphysin I and II function as multilinker proteins in the clathrin-coated complex. Under normal physiological conditions, the functions of amphiphysin I and some other endocytic proteins are known to be regulated by phosphorylation and dephosphorylation. During hyperexcited conditions, the most recent data showed that amphiphysin I is truncated by the ca2-dependent protease calpain. Overexpression of the truncated form of amphiphysin I inhibited transferrin uptake and synaptic vesicle endocytosis (SVE). This suggests that amphiphysin I may be an important regulator for SVE when massive amounts of Ca2 flow into presynaptic terminals, a phenomenon observed in neurodegenerative disorders such as ischemia/anoxia, epilepsy, stroke, trauma and Alzheimer's disease. This review describes current knowledge regarding the general properties and functions of amphiphysin I as well as the functional regulations such as phosphorylation and proteolysis in nerve terminals.