Antiviral activity of a serine protease from the digestive juice of Bombyx mori larvae against nucleopolyhedrovirus

Abstract

A protein showing strong antiviral activity against Bombyx mori nucleopolyhedrovirus (BmNPV) was purified from the digestive juice of B. mori larvae. The molecular mass of this protein was 24271 Da. Partial N-terminal amino acid sequence of the protein was determined and cDNA was cloned based on the amino acid sequence. A homology search of the deduced amino acid sequence of the cDNA showed 94% identity with B. mori serine protease so the protein was designated B. mori serine protease-2 (BmSP-2). Analysis of BmSP-2 gene expression showed that this gene is expressed in the midgut but not in other tissues. In addition, BmSP-2 gene was shown to not be expressed in the molting and wandering stages, indicating that the gene is hormonally regulated. Our results suggest that BmSP-2, an insect digestive enzyme, can be a potential antiviral factor against BmNPV at the initial site of viral infection.

Identification of a Soluble NADPH Oxidoreductase (BmNOX) with Antiviral Activites in the Gut Juice ofBombyx mori

“…16) Reports on the presence of proteins with antiviral activity displaying protease and lipase activity are also available. 11,12,16) Though the molecular size of the protein identified in our laboratory falls close to the previously reported antiviral proteins, the establishment of the molecular identity of the protein detected by us as an NADPHoxidoreductase like protein signifies that it is different from the previously reported molecules. Further, the levels of this antiviral protein in the gut juices collected from a selected set of silkworm races (multivoltine and bivoltine) indicates that the races which are tolerant to BmNPV infection had relatively higher quantities this protein in their gut juices (Fig.…”

“…Once the infection breaches the midgut epithelial barrier and propagates from infective foci to the hemocoel, however, there are few mechanisms known to account for the resistance and clearance of infection observed in some virus-host combinations. 10) The literature also suggests that insects have evolved digestive enzymes with antiviral properties, as in the case of BmSP-1, BmSP-2, 11) and Bmlipase-1, 12) that check viral propagation at the initial site of viral infection.…”

Cytopathology of Bombyx mori (Lepidoptera: Bombycidae) silk gland caused by multiple nucleopolyhedrovirus

“…We also need to consider the strains of B. mori larvae, which can show a remarkable difference regarding resistance to BmNPV (Ponnuvel et al, 2003;Yao et al, 2003;Nakazawa et al, 2004). This resistance is controlled by a polygenesis effect, which argues the existence of several defenses against viral infection such as proteases and lipases found in silkworm gut juice (Ponnuvel et al, 2003;Nakazawa et al, 2004). It could explain the results of Acharya et al (2002), referring to no infection of the silk gland.…”

“…They actually occur owing to such factors as the isolate's virulence, amount of ingested virus, larval instar, incidence of other pathogens, and ambient rearing conditions, mainly temperature, population density, and food availability (Adams and McClintock, 1991;Torquato et al, 2006a). We also need to consider the strains of B. mori larvae, which can show a remarkable difference regarding resistance to BmNPV (Ponnuvel et al, 2003;Yao et al, 2003;Nakazawa et al, 2004). This resistance is controlled by a polygenesis effect, which argues the existence of several defenses against viral infection such as proteases and lipases found in silkworm gut juice (Ponnuvel et al, 2003;Nakazawa et al, 2004).…”

Molecular cloning, expression and characterization of a novel geneβ-N-acetylglucosaminidase from Bombyxmori

“…Such methodologies provide useful approaches to identify differently expressed transcripts, because many genes can be examined simultaneously. To date, although a few BmNPV resistant genes have been reported, such as serine protease [2] and Bmlipase-1 [3], knowledge on the molecular mechanisms of Bombyx mori against this virus remains very limited.…”