Another brick in the wall. Validation of the σ1 receptor 3D model by computer-assisted design, synthesis, and activity of new σ1 ligands.

Originally considered an enigmatic polypeptide, the σ(1) receptor has recently been identified as a unique ligand-regulated protein. Many studies have shown the potential of σ(1) receptor ligands for the treatment of various diseases of the central nervous system (CNS); nevertheless, almost no information about the 3D structure of the receptor and/or the possible modes of interaction of the σ(1) protein with its ligands have been unveiled so far. With the present work we validated our σ(1) 3D homology model and assessed its reliability as a platform for σ(1) ligand structure-based drug design. To this purpose, the 3D σ(1) model was exploited in the design of 33 new σ(1) ligands and in their ranking for receptor affinity by extensive molecular dynamics simulation-based free energy calculations. Also, the main interactions involved in receptor/ligand binding were analyzed by applying a per residue free energy deconvolution and in silico alanine scanning mutagenesis calculations. Subsequently, all compounds were synthesized in our laboratory and tested for σ(1) binding activity in vitro. The agreement between in silico and in vitro results confirms the reliability of the proposed σ(1) 3D model in the a priori prediction of the affinity of new σ(1) ligands. Moreover, it also supports and corroborates the currently available biochemical data concerning the σ(1) protein residues considered essential for σ(1) ligand binding and activity.