Crystal structure of schizorhodopsin reveals mechanism of inward proton pumping
Akimitsu Higuchi, Wataru Shihoya, Masae Konno, Tatsuya Ikuta, Hideki Kandori, Keiichi Inoue, Osamu Nureki
Abstract
Significance We present a high-resolution structure of schizorhodopsin (SzR), a new rhodopsin family identified in Asgard archaea. SzRs work as light-driven inward H + pumps as bacterial xenorhodopsins. Although SzRs are phylogenetically located at an intermediate position between type-1 microbial rhodopsins and heliorhodopsins, the structure of SzR resembles that of bacteriorhodopsin. Notably, the cytoplasmic parts of the transmembrane helices in SzR are shorter than those in other microbial rhodopsin, and thus the putative H + acceptor E81 is located near the cytosol. Thus, we propose a model of untrapped inward H + release through a water-mediated transport network, which is different from xenorhodopsins, suggesting essential insights into the convergent evolution of the same molecular function in Asgard archaea and bacteria.