@article {70451,
	title = {The dark side of channelrhodopsins: intrinsic ion conductance of apo-opsins},
	journal = {Research Square},
	year = {2026},
	month = {2026 Jun 09},
	abstract = {<p>Opsins are known as proteins that bind retinal to form light-sensing rhodopsins, which mediate diverse forms of photoreception and are widely used for optogenetic control of cellular activity. Yet many opsins lack canonical retinal-binding features or, in their native biological contexts, are expressed where chromophore availability is limited, raising the question whether retinal-free opsins are silent. Here we show that retinal-free ion-transporting microbial opsins are not inert but adopt intrinsic, light-independent functional states alongside their canonical light-driven activity. Using developmental phenotyping in transgenic Drosophila melanogaster, electrophysiology in Xenopus oocytes and mammalian cells, together with structural and computational analyses, we demonstrate robust light-independent ion conductance in multiple channel-type opsins and an ion-pumping opsin. Structural modeling and molecular dynamics simulations reveal conformational rearrangements in transmembrane helices and internal water networks that are consistent with stabilization of apo-conductive states. Together, these findings establish apo-opsin activity as a defined functional state of microbial opsins, expand the current framework of rhodopsin biology, and highlight the need to consider chromophore-independent activity in both basic research and optogenetic applications.</p>
},
	doi = {10.21203/rs.3.rs-9039624/v1},
	url = {https://www.doi.org10.21203/rs.3.rs-9039624/v1},
	author = {Gao, Shiqiang and Zhang, Chong and Ma, Jie and Fukuda, Masahiro and Lin, Yiechang and Zhu, Mo and Duan, Xiao and Zhou, Lingbo and Zettner, Maximilian and Yang, Shang and Wang, Yanhui and Yu-Strzelczyk, Jing and Zheng, Qiang and Dannh{\"a}user, Sven and Kobayashi, Kazuhiro and Tajima, Seiya and Nakamura, Seiwa and Kim, Suhyang and Takeno, Yuka and Gee, Christine and Shi, Jiachen and He, Yuge and Kittel, Robert and Heckmann, Manfred and Nagel, Georg and Shen, Yin and Cory, Ben and Kato, Hideaki}
}
