Resumen de Molecular dynamics simulations of seven-transmembrane receptors
Arnau Cordomi Montoya
Seven transmembrane (7-TM) G protein coupled receptors (GPCR) constitute the largest family of integral membrane proteins in eukaryotes with more than 1000 members and encoding more than 2% of the human genome. These proteins play a key role in the transmission and transduction of cellular signals responding to hormones, neurotransmitters, light and other agonists, regulating basic biological processes. Their natural abundance together with their localization in the cell membrane makes them suitable targets for therapeutic intervention. Consequently, GPCR are proteins with enormous pharmacologic interest, representing the targets of about 50% of the currently marketed drugs. The current limitations in the experimental techniques necessary for microscopic studies of the membrane as well as membrane proteins emerged the use of computational methods and specifically molecular dynamics simulations. The lead motif of this thesis is the study of GPCR by means of this technique, with the ultimate goal of developing a methodology that can be generalized to the study of most 7-TM as well as other membrane proteins. Since the bovine rhodopsin was the only protein of the GPCR family with a known threedimensional structure at an atomic level until very recently, most of the effort is centered in the study of this receptor as a model of GPCR.The scope of this thesis is twofold. On the one hand it addresses the study of the simulation conditions, including the procedure as well as the sampling box to get optimal results, and on the other, the biological implications of the structural and dynamical behavior observed in the simulations. Specifically, regarding the methodological aspects of the work, the bovine rhodopsin has been studied using different treatments of long-range electrostatic interactions and sampling conditions, as well as the effect of sampling the protein embedded in different one-component lipid bilayers. The binding of ions to lipid bilayers in the absence of the protein has also been investigated. Regarding the biological consequences of the analysis of the MD trajectories, it has been carefully addressed the binding site of retinal and its implications in the process of isomerization after photon uptake, the alteration a group of residues constituting the so-called electrostatic lock between helices TM3 and TM6 in rhodopsin putatively used as common activation mechanism of GPCR, and the structural effects caused by the dimerization based on a recent semi-empirical model. Finally, the specific binding of ions to bacteriorhodopsin has also been studied. The main conclusion of this thesis is provide support to molecular dynamics as technique capable to provide structural and dynamical informational about membranes and membrane proteins, not currently accessible from experimental methods). Moreover, the use of an explicit lipidic environment is crucial for the study the membrane protein dynamics as well as for the protein-protein and lipidprotein interactions.
