ИСТИНА

Gamma-aminobutyric acid type A receptors (GABAAR) are the most important inhibitory transmitter receptors in the brain. We have found earlier that mefenanic acid (MFA) strongly potentiates GABA-induced currents in acutely isolated rat Purkinje cells. At concentration of 3-100 µM MFA increased the amplitude of currents with EC50 15.5 µM and maximal potentiation up to 700%. The further growth of MFA concentration caused an inhibitory effect on GABAAR which was dependent on membrane voltage. In this study, we combined electrophysiological and modeling approaches to study the mechanisms of MFA interaction with GABAAR. We have found that potentiating effects of MFA and general anesthetic etomidate (ETM) were non-additive, suggesting that MFA acts through the binding site targeted by etomidate. There are experimental data indicating that etomidate efficacy strongly depends on mutations of α1 M236 and β2 M286 residues. We have built a homology model of the open GABAAR based on the GluCl X-ray structure (3RIF) and used Monte-Carlo energy minimization (MCM) to predict the MFA binding site. We imposed distant constraints to find the ETM and MFA binding modes in the transmembrane β(+)/α(-) interface. Both ETM and MFA form H-bonds with β2 M2 R269, N265 residues and van-der-Waals contacts with hydrophobic residues β2 M3 Met286, Phe289 and α1 M1 Leu232, Pro233, Met236. In order to find an inhibitory site we pulled (and simultaneously rotated) MFA through the pore. Our calculations predict the existence of two binding sites located at 6 and 31 Å of the pore depth. In the upper site MFA interacts with charged and polar residues (20′-21′) and with hydrophobic residues (16′). In the lower site MFA interacts with hydrophobic residues from -2′, 2′ and 5′ rings and with polar residues (2′, 6′). The complete pore occlusion in the upper site is achieved by binding of two MFA molecules simultaneously. Supported by Russian Foundation for Basic Research 15-04-02010 and 17-04-00817.