Liquefaction ofAutographa californicaNucleopolyhedrovirus-Infected Insects Is Dependent on the Integrity of Virus-Encoded Chitinase and Cathepsin Genes

Abstract

We examined the role of the Autographa californica nucleopolyhedrovirus (AcMNPV)-encoded chitinase in virus pathogenesis in Trichoplusia ni larvae. In conjunction with the AcMNPV-encoded cathepsin, it promotes liquefaction of the host in the latter stages of infection. Insects infected with virus mutants lacking either the chitinase A gene (chiA) or cathepsin gene (cath) remained intact several days after death. However, if both viruses were used to infect insects, liquefaction of the host was restored. Chitinase was readily detected in AcMNPV-infected insects using a chitinase-specific antibody, but it was absent from insects infected with a chiA deletion mutant (AcchiA-). The chitinase was also detected in polyhedra purified from AcMNPV-infected insects but not in those from AcchiA-. However, polyhedra derived from a virus lacking an intact chiA were no less effective in initiating an infection in second instar T. ni larvae than those of the unmodified AcMNPV. It was also demonstrated that the virus chitinase retained high levels of activity between pH 3.0 and 10.0. In contrast, chitinases isolated from Serratia marcescens, although active under acidic conditions, rapidly lost activity above pH 7.0 illustrating that despite 57% sequence identity, the two proteins have distinct enzymic activities.

Distinct gene arrangement in the Buzura suppressaria single-nucleocapsid nucleopolyhedrovirus genome.

“…It is noteworthy that the cathepsin and chitinase genes, normally positioned in a head-to-head arrangement in all baculovirus genomes characterized so far, are located distally from each other in BusuNPV. This confirms a recent study (Hawtin et al, 1997) that the function of these two genes, involved in larval liquefaction, is not dependent on their proximal position in many baculovirus genomes.…”

“…EGT delays larval moulting and allows the virus to produce large numbers of progeny particles. The cath and the chiA genes are needed for larval liquefaction and thus aid dissemination of the virus in nature (Hawtin et al, 1997). It is plausible that an ancestral baculovirus contained some of the auxiliary genes and that the present baculovirus survived through evolution partly because of the advantages conferred by their encoded proteins.…”

Characterization of the 25K FP gene of the baculovirus Bombyx mori nucleopolyhedrovirus: implications for post-mortem host degradation.

“…4). In previous work on AcNPV, virus-encoded chitinase and cysteine protease were shown to be involved in liquefaction of virus-infected insects (Hawtin et al, 1997). Insects infected with mutants lacking either the chitinase or cysteine protease gene remained intact several days after death.…”

Genomic and Proteomic Analysis of Invertebrate Iridovirus Type 9

“…Analysis of this chitinase indicates that it is a member of the family 18 glycohydrolases (exochitinases) and is most closely related to the chitinase of a bacterial pathogen of fish, Yersinia ruckeri (57% identity), and to the chitinases of other bacteria and slime molds. Baculovirus chitinases, along with cathepsin, have been shown to be important in facilitating the release of virus from the host (15). Despite the IIV-9 chitinase displaying less than 20% identity to baculovirus chitinases, the presence of a viral cathepsin (177R pi ) in IIV-9 may reflect similar roles of chitinase and cathepsin, acting in con- on April 8, 2019 by guest http://jvi.asm.org/ cert to degrade the insect, thereby facilitating viral release and dissemination from the host insect (15).…”

“…Baculovirus chitinases, along with cathepsin, have been shown to be important in facilitating the release of virus from the host (15). Despite the IIV-9 chitinase displaying less than 20% identity to baculovirus chitinases, the presence of a viral cathepsin (177R pi ) in IIV-9 may reflect similar roles of chitinase and cathepsin, acting in con- on April 8, 2019 by guest http://jvi.asm.org/ cert to degrade the insect, thereby facilitating viral release and dissemination from the host insect (15). Both enzymes were identified in IIV-9-infected insect cells by our proteomic analysis.…”