Reaching the melting point: Degradative enzymes and protease inhibitors involved in baculovirus infection and dissemination

- Baculoviruses encode several different kinds of degradative enzymes and protease inhibitors.
- Both types of genes are uncommon in viruses.
- Baculovirus degradative enzymes digest host tissues or enhance midgut infection.
- Baculovirus protease inhibitors block caspase activity and may suppress immune responses.

Baculovirus infection of a host insect involves several steps, beginning with initiation of virus infection in the midgut, followed by dissemination of infection from the midgut to other tissues in the insect, and finally culminating in “melting” or liquefaction of the host, which allows for horizontal spread of infection to other insects. While all of the viral gene products are involved in ultimately reaching this dramatic infection endpoint, this review focuses on two particular types of baculovirus-encoded proteins: degradative enzymes and protease inhibitors. Neither of these types of proteins is commonly found in other virus families, but they both play important roles in baculovirus infection. The types of degradative enzymes and protease inhibitors encoded by baculoviruses are discussed, as are the roles of these proteins in the infection process.