Cryo-EM structure of a nanobody-bound heliorhodopsin
Ruixue Xia1, Mingxia Sun2, Yang Lu1
1HIT Center for Life Sciences, School of Life Science and Technology, Faculty of Life Sciences and Medicine, Harbin Institute of Technology, Harbin, 150001, China.
Abstract:
Heliorhodopsins (HeRs) represent a distinct class of microbial rhodopsins (MRs) with an inverted membrane topology compared to other MRs. Previous structural studies have shown that HeRs lack a proton acceptor residue, and protons are never released from the protein. In this study, we present the cryo-electron microscopy (cryo-EM) structure of HeR bound to a nanobody. The structure reveals an acetate-like molecule in the Schiff base cavity (SBC) on the intracellular side of HeR under neutral condition. Structural comparisons and analyses suggest that the acetate molecule may function as a proton acceptor for the protonated retinal Schiff base (RSB) and act as a mediator for the intramolecular signaling transduction in HeR during light stimulation. These structural insights shed new light on the mechanism and function of HeR.
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