Biochemical characterization and overexpression of an α-amylase (BmAmy) in silkworm, Bombyx mori

Silkworm (Bombyx mori) is the only fully domesticated insect. As an economically important insect, nutrition utilization is important for its productivity. Hence, the present study investigated the expression pattern of BmAmy, an α-amylase, in B. mori. BmAmy protein purification and biochemical characterization were performed, and effects of BmAmy overexpression were assessed. Real-time quantitative reverse transcription polymerase chain reaction indicated that BmAmy transcription was positively correlated with the silkworm's food intate. Moreover, enzymatic activity assay results showed that BmAmy had significant α-amylase activity of about 1 mg/min/mg protein. Furthermore, treatment with mulberry amylase inhibitors MnAI1 and MnAI2 resulted to 89.92% and 93.67% inhibition in BmAmy activity, respectively, and the interaction between BmAmy and MnAI was also confirmed by protein docking analysis. A silkworm line that specifically overexpressed BmAmy in the midgut was generated through piggyBac-based transgenic technology, and compared to those of non-transgenic silkworms, the whole cocoon and cocoon shell weights of these transgenic silkworms increased by 10.13% and 18.32%, respectively, in the female group, and by 5.83% and 6.00%, respectively, in the male group. These results suggested that BmAmy may be a suitable target for breeding better silkworm varieties in the future.