Investigating the structural impact of S311C mutation in DRD2 receptor by molecular dynamics & docking studies.

Dopamine receptors (DR) are neuronal cell surface proteins that mediate the action of neurotransmitter dopamine in brain. Dopamine receptor D2 (DRD2) that belongs to G-protein coupled receptors (GPCR) family is a major therapeutic target for of various neurological and psychiatric disorders in human. The third inter cellular loop (ICL3) in DRD2 is essential for coupling G proteins and several signaling scaffold proteins. A mutation in ICL3 can interfere with this binding interface, thereby altering the DRD2 signaling. In this study we have examined the deleterious effect of serine to cysteine mutation at position 311 (S311C) in the ICL3 region that is implicated in diseases like schizophrenia and alcoholism. An in silico structure modeling approach was employed to determine the wild type (WT) and mutant S311C structures of DRD2, scaffold proteins - Gαi/o and NEB2. Protein-ligand docking protocol was exercised to predict the interactions of natural agonist dopamine with both the WT and mutant structures of DRD2. Besides, atomistic molecular dynamics (MD) simulations were performed to provide insights into essential dynamics of the systems-unbound and dopamine bound DRD2 (WT and mutant) and three independent simulations for Gαi, Gαo and NEB2 systems. To provide information on intra-molecular arrangement of the structures, a comprehensive residue interactions network of both dopamine bound WT and mutant DRD2 protein were studied. We also employed a protein-protein docking strategy to find the interactions of scaffold proteins - Gαi/o and NEB2 with both dopamine bound WT and mutant structures of DRD2. We observed a marginal effect of the mutation in dopamine binding mechanism on the trajectories analyzed. However, we noticed a significant structural alteration of the mutant receptor which affects Gαi/o and NEB2 binding that can be causal for malfunctioning in cAMP-dependent signaling and Ca(+) homeostasis in the brain dopaminergic system leading to neuropsychiatric disorders.