Prevention of Protease-Induced Degradation of Desmoplakin via Small Molecule Binding

Desmoplakin (DSP) is a large protein (~260 kDa) localized in desmosomes, the cellular junctions that anchor the intermediate filament networks between neighboring cells. A mutation “hotspot” within the NH₂-terminal region of DSP (residues 299–515) is linked to arrhythmogenic cardiomyopathy. In certain DSP variants, disease progression is associated with increased sensitivity to degradation by calpain. Previous studies have shown that introducing a bulky residue near the cleavage site can block calpain access, restoring DSP levels in vitro. This suggests that physically hindering calpain interaction is a viable therapeutic strategy.

In this study, we aimed to identify drug-like molecules that inhibit the calpain-mediated degradation of DSP. We screened approximately 2,500 small molecules to find compounds that rescue DSP levels in the presence of proteases. Our findings revealed several effective compounds, including sodium dodecyl sulfate, palmitoylethanolamide, GW0742, salirasib, eprosartan mesylate, and GSK1838705A. These molecules prevented the degradation of both wild-type and mutant DSP by trypsin and calpain, without affecting the proteases’ activity.

Notably, computational screening failed to predict which molecules would protect DSP, likely due to the absence of specific interactions between the protein and the compounds. However, molecular dynamics simulations suggest that certain long hydrophobic molecules bind within a shallow hydrophobic groove near the cleavage site, physically blocking protease access. The identification of these compounds provides a foundation for developing pharmacological treatments targeting DSP variants associated with calpain hypersensitivity.