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Publication Abstract from PubMed

Schizorhodopsins (SzRs), a new rhodopsin family identified in Asgard archaea, are phylogenetically located at an intermediate position between type-1 microbial rhodopsins and heliorhodopsins. SzRs work as light-driven inward H(+) pumps as xenorhodopsins in bacteria. Although E81 plays an essential role in inward H(+) release, the H(+) is not metastably trapped in such a putative H(+) acceptor, unlike the other H(+) pumps. It remains elusive why SzR exhibits different kinetic behaviors in H(+) release. Here, we report the crystal structure of SzR AM_5_00977 at 2.1 A resolution. The SzR structure superimposes well on that of bacteriorhodopsin rather than heliorhodopsin, suggesting that SzRs are classified with type-1 rhodopsins. The structure-based mutagenesis study demonstrated that the residues N100 and V103 around the beta-ionone ring are essential for color tuning in SzRs. The cytoplasmic parts of transmembrane helices 2, 6, and 7 are shorter than those in the other microbial rhodopsins, and thus E81 is located near the cytosol and easily exposed to the solvent by light-induced structural change. We propose a model of untrapped inward H(+) release; H(+) is released through the water-mediated transport network from the retinal Schiff base to the cytosol by the side of E81. Moreover, most residues on the H(+) transport pathway are not conserved between SzRs and xenorhodopsins, suggesting that they have entirely different inward H(+) release mechanisms.

Crystal structure of schizorhodopsin reveals mechanism of inward proton pumping.,Higuchi A, Shihoya W, Konno M, Ikuta T, Kandori H, Inoue K, Nureki O Proc Natl Acad Sci U S A. 2021 Apr 6;118(14). pii: 2016328118. doi:, 10.1073/pnas.2016328118. PMID:33790007^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.