Short‐chain mono‐carboxylates as negative modulators of allosteric transitions in Gloeobacter violaceus ligand‐gated ion channel, and impact of a pre‐β5 strand (Loop Ω) double mutation on crotonate, not butyrate effect

Abstract

AbstractUsing the bacterial proton‐activated pentameric receptor‐channel Gloeobacter violaceus ligand‐gated ion channel (GLIC): (1) We characterize saturated, mono‐carboxylates as negative modulators of GLIC (as previously shown for crotonate; Alqazzaz et al., Biochemistry, 2016, 55, 5947). Butyrate and crotonate have indistinguishable properties regarding negative modulation of wt GLIC. (2) We identify a locus in the pre‐β5 strand (Loop Ω) whose mutation inverses the effect of the mono‐carboxylate crotonate from negative to positive modulation of the allosteric transitions, suggesting an involvement of the pre‐β5 strand in coupling the extracellular orthotopic receptor to pore gating. (3) As an extension to the previously proposed “in series” mechanism, we suggest that a orthotopic/orthosteric site—vestibular site—Loop Ω—β5‐β6 “sandwich”—Pro‐Loop/Cys‐Loop series may be an essential component of orthotopic/orthosteric compound‐elicited gating control in this pentameric ligand‐gated ion channel, on top of which compounds targeting the vestibular site may provide modulation.