α-Crystallin chaperone mimetic drugs inhibit lens γ-crystallin aggregation: Potential role for cataract prevention

Gamma-Crystallins play a major role in age-related lens transparency. Their destabilization by mutations and physical chemical insults are associated with cataract formation. Therefore, drugs that increase their stability should have anticataract properties. To this end, we screened 2560 Federal Drug Agency-approved drugs and natural compounds for their ability to suppress or worsen H2O2 and/or heat-mediated aggregation of bovine gamma-crystallins. The top two drugs, closantel (C), an antihelminthic drug, and gambogic acid (G), a xanthonoid, attenuated thermal-induced protein unfolding and aggregation as shown by turbidimetry fluorescence spectroscopy dynamic light scattering and electron microscopy of human or mouse recombinant crystallins. Furthermore, binding studies using fluorescence inhibition and hydrophobic pocketbinding molecule bis-8-anilino-1-naphthalene sulfonic acid revealed static binding of C and G to hydrophobic sites with medium-to-low affinity. Molecular docking to H gamma D and other gamma-crystallins revealed two binding sites, one in the NC pocket (residues 50-150) of H gamma D and one spanning the NC tail (residues 56-61 to 168-174 in the C-terminal domain). Multiple binding sites overlap with those of the protective mini aAcrystallin chaperone MAC peptide. Mechanistic studies using bis-8-anilino-1-naphthalene sulfonic acid as a proxy drug showed that it bound to MAC sites, improved T-m of both H2O2 oxidized and native human gamma D, and suppressed turbidity of oxidized H gamma D, most likely by trapping exposed hydrophobic sites. The extent to which these drugs act as acrystallin mimetics and reduce cataract progression remains to be demonstrated. This study provides initial insights into binding properties of C and G to gamma-crystallins.

Automated summary

The drugs closantel and gambogic acid can suppress thermal-induced protein unfolding and aggregation in gamma-crystallins. They bind to hydrophobic sites with medium-to-low affinity. Docking experiments revealed two binding sites for these drugs on gamma-crystallins, overlapping with the binding sites of the protective mini aAcrystallin chaperone MAC peptide.