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1.A.55 The Synaptic Vesicle-Associated Ca2+ Channel, Flower (Flower) Family

Synaptic vesicle (SV) exo- and endocytosis are tightly coupled to sustain neurotransmission in presynaptic terminals, and both are regulated by Ca2+. Ca2+ influx triggered by voltage-gated Ca2+ channels is necessary for SV fusion. However, extracellular Ca2+ has also been shown to be required for endocytosis. The intracellular Ca2+ levels (<1 μM) that trigger endocytosis are typically much lower than those (>10 μM) needed to induce exocytosis, and endocytosis is inhibited when the Ca2+ level exceeds 1 μM.  Yao et al., (2009) identified and characterized a 4 TMS transmembrane protein named 'Flower', associated with SVs that, upon SV fusion, localizes at periactive zones. Loss of Flower results in impaired intracellular resting Ca2+ levels and impaired endocytosis. Flower multimerizes and is able to form a channel to control Ca2+ influx. Yao et al. (2009) proposed that Flower functions as a Ca2+ channel to regulate synaptic endocytosis and hence couples exo- with endocytosis. Homologues may be present in various intrarcellular membranes.  The Flower family is also called the Cg6252-P Family.

References associated with 1.A.55 family:

Yao, C.K., Y.Q. Lin, C.V. Ly, T. Ohyama, C.M. Haueter, V.Y. Moiseenkova-Bell, T.G. Wensel, and H.J. Bellen. (2009). A synaptic vesicle-associated Ca2+ channel promotes endocytosis and couples exocytosis to endocytosis. Cell 138: 947-960. 19737521