1.A.9.9.2
Cys-loop ligand-gated pentameric cation channel of 320 aas and 4 C-terminal TMSs sTeLIC (Hu et al. 2018); from a bacterial endosymbiont of Tevnia jerichonana (vent Tica). 28% identical to ELIC (TC# 1.A.9.9.1).  The crystal structure has been determined in a wide open state, revealing a cavity for modulation.  It is gated by alkaline pH. Two charged restriction rings are present in the vestibule. Functional characterization shows sTeLIC to be a cationic channel activated at alkaline pH. It is inhibited by divalent cations, but not by quaternary ammonium ions such as tetramethylammonium. Hu et al. 2018 also found that sTeLIC is allosterically potentiated by the aromatic amino acids, Phe and Trp, as well as their derivatives, such as 4-bromo-cinnamate, whose cocrystal structure reveals a vestibular binding site equivalent to, but more deeply buried than, the one already described for benzodiazepines in ELIC. The channel is regulated by a semi-conserved cationic-lipid binding site, where the residue involved is the tryptophan, W206 (Sridhar et al. 2021).