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Cell. 2016 Nov 17;167(5):1252-1263.e10. doi: 10.1016/j.cell.2016.10.053.

The C. elegans Taste Receptor Homolog LITE-1 Is a Photoreceptor.

Author information

1
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.
2
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.
3
Life Sciences Institute and Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48109, USA.
4
Departments of Structural Biology and Developmental Neurobiology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA.
5
Department of Pharmacology, Case Western Reserve University, Cleveland, OH 44106, USA.
6
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.
7
Life Sciences Institute and Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI 48109, USA. Electronic address: shawnxu@umich.edu.

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.

KEYWORDS:

chemosensation; chemosensory; neuron; photopigment; photosensation; photosensory

PMID:
27863243
PMCID:
PMC5388352
DOI:
10.1016/j.cell.2016.10.053
[Indexed for MEDLINE]
Free PMC Article

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