Comparative model of a GABAA receptor based on the crystal structure of human β3 homopentamer.

MARÍA JULIA AMUNDARAIN; FERNANDO ZAMARREÑO; JUAN FRANCISCO VISO; MARCELO DANIEL COSTABEL

Salto

Congreso; Latin American Crosstalk in Biophysics and Physiology; 2015

Seccional Biofísica de la Sociedad Uruguaya de Biociencias

Gamma-Aminobutyric acid type A receptors, GABAARs, are the major inhibitory neurotransmitter receptors in the mammalian central nervous system. They are members of the Cys-loop family of pentameric ligand gated ion channels and assemble as a combination of multiple subunits. GABAARs are chloride-permeable and are controlled by a variety of compounds which include GABA, benzodiazepines, neurosteroids and anesthetics among others. Dysfunctional GABAARs are implicated in multiple human diseases. The 3D structure of membrane proteins is particularly difficult to obtain. Only recently it has been published the crystal structure of β3 homopentameric human GABAAR, the first member of this sub-family tobe solved so far. We used this structure as a template for homology modeling of the most abundant heteromeric GABAAR channel, the α1β2Gamma2 subtype. We made use of PROMALS to make multiple alignments of the subunits with sequences from other family members and the crystalized homopentamer. In addition, we performed manual adjustments to the alignments in relevant regions by taking into account structural information based on previous studies. The model was executed with MODELLER it comprises both the extracellular and transmembrane domains. Several steps of refinement were applied in order to get a reliable model to carry out further studies. We are particularly interested in studying the Benzodiazepines binding site with a high level of detail. This region is located in the extracellular domain between the α1 and 2 subunits.Finally we performed electrostatic analysis, normal modes calculations and stereochemistry tests to evaluate the quality of the model. Furthermore, we compared our model with previous published models with the aim of assessing the differences between closed and open conformations, as well as the improvements of using the chosen template.We would like to thank CONICET and Universidad Nacional del Sur.