title: Comparative studies of Bombyx mori nucleopolyhedrovirus chitinase and its host ortholog, BmChi-h.
abstract: Baculovirus-encoded chitinases (V-CHIAs) were first proposed to be acquired from a bacterium via horizontal gene transfer. However, we have recently reported that lepidopteran hosts also encode v-chiA orthologs. Here we describe comparative studies of Bombyx mori nucleopolyhedrovirus (BmNPV) chitinase and its host ortholog, BmChi-h. We constructed recombinant BmNPVs in which native and modified forms of BmChi-h were driven under the polyhedrin promoter and the authentic v-chiA was deleted. Western blot analysis indicated that BmCHI-h was rapidly secreted from virus-infected BmN cells whereas BmNPV CHIA was localized within the virus-infected cells; probably because of the presence of a C-terminal endoplasmic reticulum retention motif on BmNPV CHIA. Enzymological studies showed that BmNPV CHIA was able to retain much higher chitinolytic activity under alkaline conditions. For B. mori larvae infected with v-chiA-deleted BmNPV, the terminal liquefaction of dead larvae and the activation of baculovirus-encoded cysteine protease were not observed, and the introduction of BmChi-h did not rescue these defects. Our findings show that BmNPV chiA possesses unique features that are not shared by host orthologs, which may reflect functional specialization of baculovirus chitinases.
authors.affiliation: Department of Agricultural and Environmental Biology, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Yayoi 1-1-1, Bunkyo-ku, Tokyo 113-8657, Japan.
authors.forename: Takaaki
authors.initials: T
authors.lastname: Daimon
authors.forename: Susumu
authors.initials: S
authors.lastname: Katsuma
authors.forename: WonKyung
authors.initials: W
authors.lastname: Kang
authors.forename: Toru
authors.initials: T
authors.lastname: Shimada
mesh_terms: D000818:Animals; D016367:Baculoviridae / Q000201:enzymology* / Q000235:genetics / Q000472:pathogenicity / Q000502:physiology; D015153:Blotting, Western; D012831:Bombyx / Q000821:virology*; D002478:Cells, Cultured; D002688:Chitinases / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D003546:Cysteine Endopeptidases / Q000235:genetics / Q000378:metabolism; D017924:Nucleopolyhedroviruses / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D000077183:Occlusion Body Matrix Proteins; D011401:Promoter Regions, Genetic; D014764:Viral Proteins / Q000235:genetics / Q000378:metabolism; D015678:Viral Structural Proteins
chemical_list: D000077183:Occlusion Body Matrix Proteins; D014764:Viral Proteins; D015678:Viral Structural Proteins; C009829:polyhedrin protein, Nucleopolyhedrovirus; D002688:Chitinases; D003546:Cysteine Endopeptidases