Nodavirus endopeptidase

This chapter elaborates the structural chemistry and the biological aspects of nodavirus endopeptidase. The chapter discusses that because the nodavirus endoprotease activity is associated with the precursor particle; a provirion preparation is required to study the protease activity. Both Black Beetle Virus (BBV) and Flock House Virus (FHV) are propagated in Drosophila line 1 cells. To obtain provirions, cells are infected at high multiplicity and incubated until the rate of coat protein synthesis reaches maximum levels, usually for 16 hours. While assembly of provirions from newly synthesized coat protein is rapid (10 minutes), the subsequent cleavage reaction is slow, leading to a temporary accumulation of provirions in the infected cells. The autocatalytic cleavage of nodaviruses releases the C-terminal 44 residues from the subunit. The distance between the new C- and N-termini is about 7 Å. The cleaved-off polypeptide is internal and remains associated with the particle following proteolysis. Residues 364–382 of BBV and FHV form an amphipathic helix, and residues 383–407 are not visible in the electron density map, indicating that they do not have an icosahedral symmetry.