The structure of viral cathepsin from Bombyx mori Nuclear Polyhedrosis Virus 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.

Identification and characterization of a protein kinase gene in the Lymantria dispar multinucleocapsid nuclear polyhedrosis virus.

The Lymantria dispar multinucleocapsid nuclear polyhedrosis virus (LdMNPV) gene encoding vPK has been cloned and sequenced. LdMNPV vPK shows a 24% amino acid identity to the catalytic domains of the eucaryotic protein kinases nPKC from rabbits, HSPKCE from humans, APLPKCB from Aplysia californica, and dPKC98F from Drosophila melanogaster, and homology to several other protein kinases from yeasts, mice, and bovines. The homology suggests that vPK is a serine/threonine protein kinase as defined by Hanks et al. (S.K. Hanks, A.M. Quinn, and T. Hunter, Science 241:42-52, 1988). Temporal expression studies indicate that vPK is expressed throughout the infection cycle beginning at 4 h postinfection, first as a delayed-early gene and subsequently as a late gene. Sequence analysis and primer extension reactions confirm the presence of distinct early and late transcription initiation regions. Expression of vPK with a rabbit reticulocyte system generated a 31-kDa protein, which is in close agreement with the predicted size of 32 kDa from the amino acid sequence. Phosphorylation activity of in vitro-expressed vPK was demonstrated by using calf thymus histones.