In-silico assessment of a potential pharmacological chaperone for human GALNS: evaluation in a mutated protein model

Most of the missense mutations in genes of lysosomal enzymes has been associated with a disruption in protein folding leading to a degradation in the endoplasmic reticulum and limiting the enzyme able to reach the lysosome. Pharmacological chaperones (PC) could improve the folding and stabilize the structural conformation, avoiding the degradation and favoring the functionality of the enzyme. Through an in-silico drug repurposing approach using a modeled 3D structure of GALNS, we identified several candidates that bind to the active site of the enzyme and increase in-vitro the activity of the wild-type enzyme. In this study, we used the crystal structure of human GALNS (PDB 4FDI) carrying formylglycine and calcium within the active site. Site-directed mutagenesis, for five of the most prevalent mutations (I113F, S162F, G301C, R386C and T312S) and energy minimization were performed on UCSF Chimera. AutoDock Vina was used for computational molecular docking and to evaluate enzyme-ligand interactions between GALNS with keratan-sulfate (KS) and a previously identified potential PC (MoIEIM-1). Mutation T312S has a potential energy closer to that of wild-type GALNS (attenuated phenotype), while all other studied mutations had an increase in this value, which was previously associate with severe phenotypes. KS showed an affinity energy similar to that of MoIEIM-1 (-8.3 vs -8.4 kcal/mol, respectively) as well as a position and interactions very similar inside the active site. For the mutations underlined the affinity energy with KS was altered while for MoIEIM-1 the results were very similar to those of the wild-type enzyme. T312S was the only mutation for which a reduction in affinity with MoIEIM-1 was observed (-7.1 kcal/mol); while severe phenotype mutations showed improvement in protein-ligand affinity. This is first step for evaluate MoIEIM-1 in mutated GALNS and preliminary results shown the potential of this possible PC as alternative therapy for Mucopolysaccharidosis IV A.