Identification of two isoforms of Pop in the domestic silkworm, Bombyx mori: Cloning, characterization and expression analysis

Two isoforms, Bmpop-a and Bmpop-b, were cloned and characterized, which were found to encode prolyl oligopeptidase (Pop) of the domestic silkworm Bombyx mori. The full lengths of Bmpop-a and Bmpop-b were 2497 and 2508 bp, deducing 707 and 740 amino acids, respectively. Both of them, possessing the typical characteristics of the Pop family of serine proteinase, were detected to be expressed among different tissues and development stages at the transcription and translation levels. Soluble recombinant BmPop-a (rBmPop-a) had oligopeptidase activity toward the substrates, Z-Gly-Pro-pNA, Z-Gly-Pro-AMC and angiotensin I. An inhibition assay showed that the activity of rBmPop-a was significantly inhibited by KYP-2047 and S17092 in vitro. BmPop-b was identified in the molting fluids at three different stages by Western blotting analysis, showing a predominant expression in the integument. Two isoforms of Bmpop gene and other three genes in the renin-angiotensin system (RAS) in the integument were down-regulated by starvation treatments but up-regulated by refeeding. These results suggested that BmPops may play an important role in balancing the molting fluid pressure to guarantee ecdysis normally. This study provides clues for further elucidating the function and regulation mechanisms of two isoforms of Bmpop gene.