3.E.1.1.14
Synechocystis halorhodopsin of 234 aas and 7 TMSs.  The 3-D structure is known (Astashkin et al. 2022). MRs can pump various monovalent ions like Na⁺, K⁺, Cl^-, I-, and NO₃^-. The only characterized MR proposed to pump sulfate in addition to halides belongs to the cyanobacterium Synechocystis sp. PCC 7509 and is named Synechocystis halorhodopsin (SyHR).  Astashkin et al. 2022 presented the crystal structure of SyHR in the ground state, the structure of its sulfate-bound form as well as two photoreaction intermediates, the K and O states. The data reveal the molecular origin of the unique properties of the protein (exceptionally strong chloride binding and proposed pumping of divalent anions) and sheds light on the mechanism of anion release and uptake in cyanobacterial halorhodopsins. The unique properties of SyHR highlight its potential as an optogenetics tool and may help engineer different types of anion pumps with applications in optogenetics (Astashkin et al. 2022).