Study of the allosteric potentiation mechanism of the α9α10 cholinergic nicotinic receptor by extracellular calcium

SOFIA GALLINO; PATRICIO O. CRAIG; JUAN BOFFI; PAOLA PLAZAS; A BELEN ELGOYHEN

Congreso; XXXVII Congreso Anual de la Sociedad Argentina de Investigaciones en Neurociencias; 2022

The α9α10 nicotinic cholinergic receptor (nAChR) is an ion channel that is composed of α9 and α10 subunits. Each nAChR subunit comprises a large extracellular amino-terminal domain, four transmembrane domains (TM1-TM4), a long cytoplasmic loop between TM3 and TM4 and a C-terminal domain. One of the functional differences between α9 and α9α10 nAChRs is the modulation of their ACh-evoked responses by extracellular Ca2+. While α9 nAChRs responses are blocked by Ca2+, ACh-evoked currents through α9α10 nAChRs are potentiated by Ca2+ in the micromolar range and blocked at millimolar concentrations. In order to identify the structural determinants responsible for these differences, we generated chimeric and mutant α10 subunits, expressed them in Xenopus oocytes and performed electrophysiological recordings under two electrode voltage clamp. Our results suggest that the TM2-TM3 loop of the α10 subunit contains key structural determinants for the potentiation of the α9α10 nAChR by Ca2+.Moreover, to elucidate the mechanism of this potentiation by extracellular Ca2+ we performed molecular dynamics simulations of the interaction of Ca2+ with different nAChRs models. The result shows that both heteromeric α9α10 and homomeric α9 nAChRs exhibit similar Ca2+ binding in the environment of their TM2-TM3 loops. Therefore, our hypothesis is that the TM2-TM3 loop of the α10 subunit contributes with structural determinants that are key for the gating of the α9α10 nAChR in the presence of Ca2+