G protein-coupled receptor-bioligand interactions modeled in a phospholipid bilayer

The arginine vasopressin (AVP) V2 receptor (V2R), a member of the G protein -coupled receptor (GPCR) superfamily, mediates the regulation of renal wate r absorption whose disorders cause nephrogenic diabetes insipidus. A comple te molecular model of V2R embedded in a fully hydrated dimyristoylphosphati dylcholine (DMPC) bilayer was developed. Both free and AVP-bound states of V2R were studied. An initial V2R was built using a rule-based automated met hod for GPCR modeling, implementing both the low-resolution structure of bo vine rhodopsin and the multisequence analysis of the GPCR superfamily. The loops were added using homology modeling as implemented in SYBYL. The docki ng site of AVP was selected and justified upon consideration of ligand-rece ptor interactions versus structure-activity data. The model was initially r elaxed using constrained simulated annealing in vacuo. Subsequently, it was placed in the relaxed fully hydrated DMPC bilayer and submitted to similar to 1.5 ns molecular dynamics using the AMBER 4.1 package upon constant num ber-pressure-temperature (NPT) conditions on parallel computers: Gray T3E a nd/or IBM SP2. Physical properties of the system were evaluated and compare d with a pure hydrated DMPC bilayer. The receptor-ligand interactions, solv ation interactions, individual lipid-protein interactions, and fluctuations of the protein, the lipid, and water were analyzed in detail. Receptor res idues likely to be involved in the Ligand binding were selected. As expecte d, the membrane-spanning helices of the protein fluctuate less than do the peripheral loops. The protein locally disturbs the Lipid structure. A conti guous network of polar residues, extending from the bottom of the docked-li gand to the intracellular domain, is observed inside the receptor in the AV P-bound V2R, while a similar network is broken in the empty V2R. This obser vation may suggest possible active and resting states of V2R, respectively. (C) 1999 John Wiley & Sons, Inc. Int J Quant Chem 73: 61-70, 1999.