GABA A receptors are pentameric ligand-gated ion channels involved in fast inhibitory neurotransmission and are allosterically modulated by the anxiolytic, anticonvulsant, and sedative-hypnotic benzodiazepines. Here we show that the prokaryotic homolog ELIC also is activated by GABA and is modulated by benzodiazepines with effects comparable to those at GABA A receptors. Crystal structures reveal important features of GABA recognition and indicate that benzodiazepines, depending on their concentration, occupy two possible sites in ELIC. An intrasubunit site is adjacent to the GABA-recognition site but faces the channel vestibule. A second intersubunit site partially overlaps with the GABA site and likely corresponds to a low-affinity benzodiazepine-binding site in GABA A receptors that mediates inhibitory effects of the benzodiazepine flurazepam. Our study offers a structural view how GABA and benzodiazepines are recognized at a GABA-activated ion channel.

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Influenza is an infectious disease that represents an important public health burden, with high impact on the global morbidity, mortality, and economy. The poor protection and the need of annual updating of the anti-influenza vaccine, added to the rapid emergence of viral strains resistant to current therapy make the need for antiviral drugs with novel mechanisms of action compelling. In this regard, the viral RNA polymerase is an attractive target that allows the design of selective compounds with reduced risk of resistance. In previous studies we showed that the inhibition of the polymerase acidic protein-basic protein 1 (PA-PB1) interaction is a promising strategy for the development of anti-influenza agents. Starting from the previously identified 3-cyano-4,6-diphenyl-pyridines, we chemically modified this scaffold and explored its structure-activity relationships. Noncytotoxic compounds with both the ability of disrupting the PA-PB1 interaction and antiviral activity were identified, and their mechanism of target binding was clarified with molecular modeling simulations.

The actions of a novel, potent 5-HT 3 receptor ligand, [2-chloro-(4-methylpiperazine-1-yl)quinoxaline (VUF10166)], were examined at heterologously expressed human 5-HT 3 A and 5-HT 3 AB receptors. VUF10166 displaced [3 H]granisetron binding to 5-HT 3 A receptors expressed in human embryonic kidney cells with high affinity (K i ϭ 0.04 nM) but was less potent at 5-HT 3 AB receptors (K i ϭ 22 nM). Dissociation of [3 H]granisetron in the presence of VUF10166 was best fit with a single time constant (t 1/2 ϭ 53 min) at 5-HT 3 A receptors, but with two time constants (t 1/2 ϭ 55 and 2.4 min) at 5-HT 3 AB receptors. Electrophysiological studies in oocytes revealed that VUF10166 inhibited 5-HT-induced responses at 5-HT 3 A receptors at nanomolar concentrations, but inhibition and recovery were too slow to determine an IC 50 . At 5-HT 3 AB receptors, inhibition and recovery were faster, yielding an IC 50 of 40 nM. Cysteine substitutions in the complementary (Ϫ), but not the principal (ϩ), face of the 5-HT 3 B subunit produced heteromeric receptors in which the actions of VUF10166 resembled those at homomeric receptors. At 5-HT 3 A receptors, VUF10166 at higher concentrations also behaved as a partial agonist (EC 50 ϭ 5.2 M; R max ϭ 0.24) but did not elicit significant responses at 5-HT 3 AB receptors at Յ100 M. Thus, we propose that VUF10166 binds to the common AϩAϪ site of both receptor types and to a second AϩBϪ modulatory site in the heteromeric receptor. The ability of VUF10166 to distinguish between 5-HT 3 A and 5-HT 3 AB receptors could help evaluate differences between these receptor types and has potential therapeutic value.

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