“…The residues at these positions play critical roles in other types of microbial rhodopsins. Furthermore, there is a substantial correlation between the function and motif types especially in ion-pumping rhodopsins [2,16]: e.g., DTD/DTE/DTK/DTG/DTS: outward H + pump [10,[17][18][19], TSA/TSD/TTD/NTQ: inward Cl − pump [20][21][22][23], NDQ: outward H + pump [5], FSD/FSE: inward H + pump, etc. Interestingly, xenorhodopsins (XeR), a group of inward H +pumping rhodopsins [24], show diversified motifs (DSX/DTX where X is A, I, L, M S, or T).…”