Enhancin, the granulosis virus protein that facilitates nucleopolyhedrovirus (NPV) infections, is a metalloprotease.

Enhancin is a Trichoplusia ni granulovirus protein that facilitates nucleopolyhedrovirus (NPV) infections in lepidopterans. Gel filtration and ion exchange chromatography and immobilized alpha-macroglobulin were used to purify this protein and the removal of the contaminating proteases did not diminish the in vivo or in vitro activity of enhancin. Metal chelators were the only protease inhibitors capable of preventing digestion of the peritrophic membrane (PM) proteins by enhancin, indicating that enhancin is a metalloprotease. In addition, the canonical zinc binding site, HEXXH, found in most metalloproteases, was identified in the sequences of enhancins from three different granuloviruses. The identity of enhancin as a metalloprotease that facilitates NPV infections in lepidopterous larvae was confirmed by the expression of enhancin in a recombinant Autographa californica MNPV-baculovirus system and the purification of a recombinant enhancin that was active in neonate bioassays and that digested specific PM proteins. The recombinant enhancin was also inhibited by metal chelators and both the native and recombinant enhancin could be reactivated by divalent ions, further confirming that enhancin is a metalloprotease.