The GTP- and Phospholipid-Binding Protein TTD14 Regulates Trafficking of the TRPL Ion Channel in Drosophila Photoreceptor Cells.
Recycling of signaling proteins is a common phenomenon in diverse signaling pathways. In photoreceptors of Drosophila, light absorption by rhodopsin triggers a phospholipase Cβ-mediated opening of the ion channels transient receptor potential (TRP) and TRP-like (TRPL) and generates the visual response. The signaling proteins are located in a plasma membrane compartment called rhabdomere. The major rhodopsin (Rh1) and TRP are predominantly localized in the rhabdomere in light and darkness. In contrast, TRPL translocates between the rhabdomeral plasma membrane in the dark and a storage compartment in the cell body in the light, from where it can be recycled to the plasma membrane upon subsequent dark adaptation. Here, we identified the gene mutated in trpl translocation defective 14 (ttd14), which is required for both TRPL internalization from the rhabdomere in the light and recycling of TRPL back to the rhabdomere in the dark. TTD14 is highly conserved in invertebrates and binds GTP in vitro. The ttd14 mutation alters a conserved proline residue (P75L) in the GTP-binding domain and abolishes binding to GTP. This indicates that GTP binding is essential for TTD14 function. TTD14 is a cytosolic protein and binds to PtdIns(3)P, a lipid enriched in early endosome membranes, and to phosphatidic acid. In contrast to TRPL, rhabdomeral localization of the membrane proteins Rh1 and TRP is not affected in the ttd14P75L mutant. The ttd14P75L mutation results in Rh1-independent photoreceptor degeneration and larval lethality suggesting that other processes are also affected by the ttd14P75L mutation. In conclusion, TTD14 is a novel regulator of TRPL trafficking, involved in internalization and subsequent sorting of TRPL into the recycling pathway that enables this ion channel to return to the plasma membrane.
Department of Biosensorics, Institute of Physiology, University of Hohenheim, Stuttgart, Germany.
Alexander C
AC
Cerny
Department of Biosensorics, Institute of Physiology, University of Hohenheim, Stuttgart, Germany.
André
A
Altendorfer
Department of Biosensorics, Institute of Physiology, University of Hohenheim, Stuttgart, Germany.
Krystina
K
Schopf
Department of Biosensorics, Institute of Physiology, University of Hohenheim, Stuttgart, Germany.
Karla
K
Baltner
Department of Biosensorics, Institute of Physiology, University of Hohenheim, Stuttgart, Germany.
Nathalie
N
Maag
Department of Cell and Matrix Biology, Institute of Zoology, Johannes Gutenberg-University of Mainz, Mainz, Germany.
Elisabeth
E
Sehn
Department of Cell and Matrix Biology, Institute of Zoology, Johannes Gutenberg-University of Mainz, Mainz, Germany.
Uwe
U
Wolfrum
Department of Biosensorics, Institute of Physiology, University of Hohenheim, Stuttgart, Germany.
Armin
A
Huber
D000818:Animals; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D003624:Darkness; D029721:Drosophila Proteins / Q000235:genetics* / Q000378:metabolism; D004331:Drosophila melanogaster; D005123:Eye / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000235:genetics*; D008027:Light; D008565:Membrane Proteins / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D017956:Photoreceptor Cells, Invertebrate / Q000378:metabolism*; D021381:Protein Transport / Q000235:genetics*; D012243:Rhodopsin / Q000378:metabolism; D015398:Signal Transduction; D050051:Transient Receptor Potential Channels / Q000235:genetics* / Q000378:metabolism
D029721:Drosophila Proteins; D008565:Membrane Proteins; D050051:Transient Receptor Potential Channels; C074192:trpl protein, Drosophila; D012243:Rhodopsin; D019204:GTP-Binding Proteins; C000607993:TTD14 protein, Drosophila