The structure of viral cathepsin from <i>Bombyx mori Nuclear Polyhedrosis Virus</i> as a target against grasserie: docking and molecular dynamics simulations

The viral cathepsin from Bombyx mori Nuclear Polyhedrosis Virus (BmNPV-Cath) is a broad-spectrum protease that participates in the horizontal transmission of this virus in silkworm by facilitating solubilization of the integument of infected caterpillars. When a B. mori farm is attacked by BmNPV, there are significant sericultural losses because no drugs or therapies are available. In this work, the structure of viral cathepsin BmNPV-Cath was used as a target for virtual screening simulations, aiming to identify potential molecules that could be used to treat the infection. Virtual screening of the Natural Products library from the Zinc Database selected four molecules. Theoretical calculations of ΔGbinding by the molecular mechanics Poisson–Boltzmann surface analysis (MM-PBSA) method indicated that the molecule Zinc12888007 (Bm5) would have high affinity for the enzyme. The in vivo infection models of B. mori caterpillars with BmNPV showed that treatment with a dose of 100 μg Bm5 dissolved in Pluronic-F127 0.02% was able to reduce the mortality of caterpillars in 22.6%, however, it did not impede the liquefaction of dead bodies. Our results suggest a role of BmNPV-Cath in generating a pool of amino acids necessary for viral replication and indicate a mechanism to be exploited in the search for treatments for grasserie disease of the silkworm.