title: The C. elegans Taste Receptor Homolog LITE-1 Is a Photoreceptor.
abstract: Many animal tissues/cells are photosensitive, yet only two types of photoreceptors (i.e., opsins and cryptochromes) have been discovered in metazoans. The question arises as to whether unknown types of photoreceptors exist in the animal kingdom. LITE-1, a seven-transmembrane gustatory receptor (GR) homolog, mediates UV-light-induced avoidance behavior in C. elegans. However, it is not known whether LITE-1 functions as a chemoreceptor or photoreceptor. Here, we show that LITE-1 directly absorbs both UVA and UVB light with an extinction coefficient 10-100 times that of opsins and cryptochromes, indicating that LITE-1 is highly efficient in capturing photons. Unlike typical photoreceptors employing a prosthetic chromophore to capture photons, LITE-1 strictly depends on its protein conformation for photon absorption. We have further identified two tryptophan residues critical for LITE-1 function. Interestingly, unlike GPCRs, LITE-1 adopts a reversed membrane topology. Thus, LITE-1, a taste receptor homolog, represents a distinct type of photoreceptor in the animal kingdom.
authors.affiliation: College of Life Science and Technology, Collaborative Innovation Center for Brain Science, and Key Laboratory of Molecular Biophysics of MOE, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China; Life Sciences Institute and Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48109, USA.
authors.forename: Jianke
authors.initials: J
authors.lastname: Gong
authors.affiliation: Life Sciences Institute and Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48109, USA; Department of Pharmacology, Case Western Reserve University, Cleveland, OH 44106, USA.
authors.forename: Yiyuan
authors.initials: Y
authors.lastname: Yuan
authors.affiliation: Life Sciences Institute and Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48109, USA.
authors.forename: Alex
authors.initials: A
authors.lastname: Ward
authors.affiliation: Life Sciences Institute and Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48109, USA.
authors.forename: Lijun
authors.initials: L
authors.lastname: Kang
authors.affiliation: College of Life Science and Technology, Collaborative Innovation Center for Brain Science, and Key Laboratory of Molecular Biophysics of MOE, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China; Life Sciences Institute and Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48109, USA.
authors.forename: Bi
authors.initials: B
authors.lastname: Zhang
authors.affiliation: Departments of Structural Biology and Developmental Neurobiology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA.
authors.forename: Zhiping
authors.initials: Z
authors.lastname: Wu
authors.affiliation: Departments of Structural Biology and Developmental Neurobiology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA.
authors.forename: Junmin
authors.initials: J
authors.lastname: Peng
authors.affiliation: Department of Pharmacology, Case Western Reserve University, Cleveland, OH 44106, USA.
authors.forename: Zhaoyang
authors.initials: Z
authors.lastname: Feng
authors.affiliation: College of Life Science and Technology, Collaborative Innovation Center for Brain Science, and Key Laboratory of Molecular Biophysics of MOE, Huazhong University of Science and Technology, Wuhan, Hubei 430074, China. Electronic address: jfliu@mail.hust.edu.cn.
authors.forename: Jianfeng
authors.initials: J
authors.lastname: Liu
authors.affiliation: Life Sciences Institute and Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48109, USA. Electronic address: shawnxu@umich.edu.
authors.forename: X Z Shawn
authors.initials: XZS
authors.lastname: Xu
mesh_terms: D000818:Animals; D017173:Caenorhabditis elegans / Q000378:metabolism* / Q000528:radiation effects; D029742:Caenorhabditis elegans Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D017785:Photons; D011487:Protein Conformation; D014364:Tryptophan / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: D029742:Caenorhabditis elegans Proteins; D008565:Membrane Proteins; C532483:lite-1 protein, C elegans; D014364:Tryptophan
keywords: chemosensation; chemosensory; neuron; photopigment; photosensation; photosensory