The Dual Behaviour of a GPCR Involved in Brain Damage an Repair: Forced Unbinding of the Receptor GPR17 Ligands from Wild Type and R255I Mutant Models Through a Computational Approach

GPR17 is a hybrid G-protein-coupled receptor activated by two unrelated ligand families, extracellular nucleotides and cysteinyl-leukotrienes, and involved in brain damage and repair. Its exploitment as a target for novel neuroreparative strategies depends on the elucidation of the molecular determinants driving binding of its ligands. We applied docking and molecular dynamics simulations to analyse the binding and the forced unbinding of two GPR17 ligands (the purinergic agonist UDP and the leukotriene receptor antagonist pranlukast) from both the wild-type receptor and a mutant model, where a basic residue hypothesized to be crucial for nucleotide binding had been mutated (R255I). Molecular dynamics suggested that GPR17 nucleotide binding pocket is enclosed between the helical bundle and EL2. The driving interaction involves R255 and the UDP phosphate moiety. Steered molecular dynamics experiments showed that the energy required to unbind UDP is higher for the wild-type receptor than for R255I. Three potential binding sites for pranlukast were found. In one of its preferential docking conformations, pranlukast tetrazole group is close to R255 and phenyl rings are placed into a subpocket highly conserved among GPCRs. Pulling forces developed to break polar and aromatic interactions of pranlukast were comparable. No differences between the wild-type receptor and the R255I receptor were found for the unbinding of pranlukast. These data suggest a crucial role for R255 in binding of nucleotides to GPR17. Aromatic interactions are instead likely to play a predominant role in the recognition of pranlukast, suggesting that two different binding subsites are present on GPR17.