Theoretical evaluation of a bulky <i>ortho</i> -thioalkyl-azobenzene as an alternative to photocontrol structural cytotoxic effects of metal-free and disulfide oxidized hSOD1 in pathogenesis of ALS

This study presents a novel photopharmacological strategy to mitigate the cytotoxic effects of apo-hSOD1^S-S, a misfolded protein implicated in neurodegenerative diseases. Using quantum chemical calculations and molecular dynamics simulations, we demonstrate that <i>ortho</i>-thio-substituted azobenzene photoswitches (<i>ortho</i>-TABPs) can be employed to precisely modulate the dynamics of the crucial electrostatic loop (EL) in apo-hSOD1^S-S. We establish that larger <i>ortho-S</i>-alkyl substituents on the <i>ortho</i>-TABP enhance its redox stability, favouring the <i>cis</i> conformation through the modulation of the position of the <i>n</i> → π* transition. This stability is crucial for operation within the reducing cellular environment. Furthermore, we demonstrate the successful and consistent photomodulation of EL conformational dynamics in apo-hSOD1^S-S through covalent tethering of an <i>ortho</i>-TABP. This control is achieved by leveraging the thermodynamically stable <i>trans</i> conformation of the photoswitch, which allosterically influences the EL and consequently, the geometry of the Zn-binding site, a critical determinant of apo-hSOD1^S-S cytotoxicity. This work paves the way for developing targeted therapies for neurodegenerative diseases by demonstrating the precise and effective photomodulation of apo-hSOD1^S-S <i>via</i> rationally designed <i>ortho</i>-TABPs.