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.
Mammalian Ca2+ channel, Flower, homologue, isoform a (Yao et al., 2009).
Flower of Homo sapiens (Q9UGQ2)
Insect Ca2+ channel, Flower (194 aas; 4 putative TMSs)
Flower of Drosophila melanogaster (Q95T12)
Roundworm Flower homologue (166aas)
Flower homologue of Caenorhabditis elegans (Q93533)
Flower homologue of 175 aas and 3 putative TMSs
Flower homologue of Capsaspora owczarzaki
Flower homologue of 193 aas
Fower homologue of Salpingoeca rosetta
Flatworm Flower homologue (195aas)
Flower homologue of Schistosoma japonicum (Q5DFV8)
Fungal flower homologue (149aas)
Flower homologue of Aspergillus flavus (B8N1Q6)
The yeast Tvp18p protein of 102 aas and 2 TMSs.
Tvp180 of Saccharomyces cerevisiae
Uncharacterized protein of 127 aas and 4 TMSs
UP of Blastocystis hominis
Uncharacterized protein of 151 aas and 3-4 putative TMSs.
UP of Ectocarpus siliculosus (Brown alga)
Uncharacterized protein of 176 aas and 3 TMSs
UP of Dictyostelium fasciculatum
Uncharacterized protein of 154 aas and 3 TMSs
UP of Dictyostelium discoideum