Gene analysis of an antiviral protein SP-2 from Chinese wild silkworm, Bombyx mandarina Moore and its bioactivity assay.

The cDNA encoding an antiviral protein SP-2 against BmNPV was cloned from the midgut of Chinese wild silkworm, Bombyx mandarina Moore (GenBank access AY945210) based on the available information of the domesticated silkworm. Its cDNA was 855 bp encoding 284 amino acids with predicted molecular weight of 29.6 kDa. Its full length in genomics was 1376 bp, including 5 exons and 4 introns. The expression analysis indicated that it was only expressed in midgut, and its expression level was higher during feeding stage of larval instars while very lower during the moltism and mature stages. The deduced amino acid sequence of this protein showed eight-amino-acid variation compared with the counterpart of domesticated silkworm. Its antiviral activity was assayed through in vitro test. The results indicated that it showed strong bioactivity against BmNPV, and its activity was 1.6 fold higher that the counterpart of domesticated silkworm.