MODELING, REFINEMENT AND INCLUSION IN A LIPID BILAYER OF AN ACETYLCHOLINE RECEPTOR AND ITS INTERACTION WITH FREE FATTY ACIDS

AMUNDARAIN, MARÍA JULIA; OMAR JAURE; JUAN FRANCISCO VISO; FERNANDO ZAMARREÑO; MARCELO D. COSTABEL

Ciudad Autonoma de Buenos Aires

Congreso; Reunión Conjunta de Sociedades de Biociencias; XLVI Reunión Anual de la Sociedad Argentina de Biofísica; 2017

SAB-SAB-SAIC-SAIB-SAI-SAA-SAFE-SAFIS-SAH-SAP

The free fatty acids (FFAs) act as noncompetitive antagonistsof the nicotinic acetylcholine receptor (nAChR) and its site of ac-tion would be in the lipid-AChR interface being the key factor forreceptor blockade the position and isomery of the double bond ofthe FFAs. The nAChR is a ligand-triggered ion channel, is compo-sed of 4 different polypeptide chains in a pentameric arrangement(a2bgd). Each subunit has an extracellular N-terminal domain,four transmembrane domains and a small C-terminal domain.Because of the AChR is a membrane protein little high-resolutioninformation is available on its atomic structure. Our objective wasto obtain a computational model of AChR inserted in a lipid bilayerand to study its interaction with its lipid environment and its interac-tions with the different free fatty acids in study (cis-18:1 ω-6, cis ω-9, cis-18:1 ω-11 o cis-18:1 ω-13). We made use of MODELLER tomake multiple alignments of the subunits with sequences from otherfamily members. The development of the model and its refinement,that include both extracellular and transmembrane domains, wasalso carried out with MODELLER. Using CHARMM-GUI MembraneBuilder we built and simulated lipid bilayers (composed with a ra-tio 1:1:3 of cholesterol, POPA (palmitoyl oleoyl phosphatidylamine)and POPC (palmitoyl oleoyl phosphatidylcholine) respectively), withAChR incorporated to the membrane. We are particularly interestedin studying surrounding lipids to TM4 since previous studies suggestthat M4 helix acts as a lipid-sensor that relates the properties of thebilayer to the AChR. We replace the lipid membrane closest to TM4with one of the FFAs of interest using PYMOL.Finally, we performed electrostatic analysis, normal modes cal-culations and stereochemistry tests to evaluate the quality of themodel. We performed molecular dynamics with GROMACS for eachsystem built.