MerMAIDs: A novel family of metagenomically discovered, marine, anion-conducting and intensely desensitizing channelrhodopsins

Abstract

20(J.W.) 21 MerMAID1 as a model. Replacement of Cl − with Br − or NO 3 − resulted in negative reversal potential 131 shifts (Figs. 2d and S4b), thus revealing nonselective anion conductivity, as previously reported 132 for other ACRs 21,23 . In contrast, substitution of Na + with NMDG + , Ca 2+ , or Mg 2+ had only a slight 133 effect on reversal potentials ( Fig. 2d and S4b), thereby excluding a substantial contribution by 134 cations as charge carriers. 135Rhodopsin function often commonly involves de-and reprotonation of internal amino acids, and 136 pH changes can significantly affect photocurrent amplitude and kinetics 4,9,18,19 . We therefore 137 investigated the effect of extra-and intracellular pH (pH e and pH i ) changes on MerMAID1. 138 Variation of pHe between 6.0 and 8.0 slightly altered the photocurrent amplitude ( Fig. S4c) but not 139 the reversal potential ( Figs. 2d and S4d), thus excluding proton transport. Neither pH i nor pH e 140 (2002). 595

Convergent evolution of animal and microbial rhodopsins

“…In 1999, microbial rhodopsin genes were found in the eukaryotic fungus Neurospora crassa. 79,80 Since then, more than millions of microbial rhodopsins have been identied from not only archaea but also bacteria, eukaryotic microorganisms, and viruses with a variety of distinct molecular functions, 1,10,11 such as outward proton pumps, [81][82][83][84] inward proton pumps, [85][86][87] cation channels, [88][89][90] anion channels, 91,92 inward chloride pumps, 93,94 outward sodium pumps, 95,96 a sulfate transporter, 97 transcriptional regulators, 98,99 and enzymes (e.g., histidine kinase and adenylyl/ guanylyl cyclases) 100,101 (Fig. 5A).…”