title: TMEM16B, a novel protein with calcium-dependent chloride channel activity, associates with a presynaptic protein complex in photoreceptor terminals.
abstract: Photoreceptor ribbon synapses release glutamate in response to graded changes in membrane potential evoked by vast, logarithmically scalable light intensities. Neurotransmitter release is modulated by intracellular calcium levels. Large Ca(2+)-dependent chloride currents are important regulators of synaptic transmission from photoreceptors to second-order neurons; the molecular basis underlying these currents is unclear. We cloned human and mouse TMEM16B, a member of the TMEM16 family of transmembrane proteins, and show that it is abundantly present in the photoreceptor synaptic terminals in mouse retina. TMEM16B colocalizes with adaptor proteins PSD95, VELI3, and MPP4 at the ribbon synapses and contains a consensus PDZ class I binding motif capable of interacting with PDZ domains of PSD95. Furthermore, TMEM16B is lost from photoreceptor membranes of MPP4-deficient mice. This suggests that TMEM16B is a novel component of a presynaptic protein complex recruited to specialized plasma membrane domains of photoreceptors. TMEM16B confers Ca(2+)-dependent chloride currents when overexpressed in mammalian cells as measured by halide sensitive fluorescent protein assays and whole-cell patch-clamp recordings. The compartmentalized localization and the electrophysiological properties suggest TMEM16B to be a strong candidate for the long sought-after Ca(2+)-dependent chloride channel in the photoreceptor synapse.
authors.affiliation: Institut für Humangenetik, Universität Regensburg, 93053 Regensburg, Germany. heidi.stoehr@klinik.uni-regensburg.de
authors.forename: Heidi
authors.initials: H
authors.lastname: Stöhr
authors.forename: Julia B
authors.initials: JB
authors.lastname: Heisig
authors.forename: Peter M
authors.initials: PM
authors.lastname: Benz
authors.forename: Simon
authors.initials: S
authors.lastname: Schöberl
authors.forename: Vladimir M
authors.initials: VM
authors.lastname: Milenkovic
authors.forename: Olaf
authors.initials: O
authors.lastname: Strauss
authors.forename: Wendy M
authors.initials: WM
authors.lastname: Aartsen
authors.forename: Jan
authors.initials: J
authors.lastname: Wijnholds
authors.forename: Bernhard H F
authors.initials: BH
authors.lastname: Weber
authors.forename: Heidi L
authors.initials: HL
authors.lastname: Schulz
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000818:Animals; D000075368:Anoctamins; D002118:Calcium / Q000378:metabolism; D002461:Cell Line, Transformed; D018118:Chloride Channels / Q000502:physiology*; D003001:Cloning, Molecular; D000076122:Disks Large Homolog 4 Protein; D004558:Electric Stimulation; D005123:Eye / Q000166:cytology; D015870:Gene Expression; D051528:Guanylate Kinases; D006801:Humans; D066298:In Vitro Techniques; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D008164:Luminescent Proteins / Q000235:genetics; D008564:Membrane Potentials / Q000235:genetics / Q000502:physiology; D008565:Membrane Proteins / Q000737:chemistry / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008958:Models, Molecular; D009474:Neurons / Q000166:cytology*; D054731:PDZ Domains / Q000502:physiology; D018408:Patch-Clamp Techniques; D010786:Photoreceptor Cells / Q000166:cytology*; D017729:Presynaptic Terminals / Q000378:metabolism*; D012160:Retina / Q000166:cytology; D013569:Synapses / Q000378:metabolism*; D014162:Transfection
chemical_list: C521849:ANO2 protein, human; D048868:Adaptor Proteins, Signal Transducing; D000075368:Anoctamins; D018118:Chloride Channels; D000076122:Disks Large Homolog 4 Protein; C501447:Dlg4 protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; C114672:Lin7c protein, mouse; D008164:Luminescent Proteins; D008565:Membrane Proteins; C477071:Mpp4 protein, mouse; D051528:Guanylate Kinases; D002118:Calcium