Serine protease Bm-SP142 was differentially expressed in resistant and susceptible Bombyx mori strains, involving in the defence response to viral infection.

Bm-SP142 is a 35 kDa protease in the silkworm, but its exact functions remain unknown. In this study, sequence alignment revealed that the His-Asp-Ser catalytic triad is embedded in the TAAHC-DIAL-GDSGGP sequence motif, establishing Bm-SP142 as a serine protease. Soluble recombinant GST-BmSP142 was expressed and purified, and serine protease activity was confirmed in vitro. RT-qPCR results indicated that Bm-SP142 was mainly expressed in the middle part of the silkworm midgut, and Bm-SP142 transcripts were significantly up-regulated at 24 hours post infection (hpi) in BmBDV-resistant strains (798) inoculated with BmBDV and BmNPV-resistant strains (NB) inoculated with BmNPV, but not in BmBDV-susceptible strains (306). Surprisingly, transcripts were significantly down-regulated at 12 hpi in BmNPV-susceptible strains (HuaBa 35) inoculated with BmNPV, compared with healthy silkworms. Recombinant BmNPV treated with purified Bm-SP142 effectively impaired its ability to infect BmN cells, and Bm-SP142 decreases the efficiency of BmNPV and BmBDV propagation in silkworms. Furthermore, overexpression of Bm-SP142 in BmN cells inhibited viral propagation.

Bm - SP142是家蚕中一种35 kDa的蛋白酶，但其确切功能仍不清楚。在本研究中，序列比对显示组氨酸 - 天冬氨酸 - 丝氨酸催化三联体嵌入TAAHC - DIAL - GDSGGP序列基序中，确定Bm - SP142为一种丝氨酸蛋白酶。可溶性重组GST - BmSP142被表达和纯化，并且丝氨酸蛋白酶活性在体外得到证实。实时定量PCR结果表明，Bm - SP142主要在家蚕中肠中部表达，在接种家蚕二分浓核病毒（BmBDV）的抗BmBDV品系（798）和接种家蚕核型多角体病毒（BmNPV）的抗BmNPV品系（NB）中，Bm - SP142的转录本在感染后24小时（hpi）显著上调，但在易感BmBDV的品系（306）中没有上调。令人惊讶的是，与健康家蚕相比，接种BmNPV的易感BmNPV品系（华八35）中，转录本在感染后12小时显著下调。用纯化的Bm - SP142处理的重组BmNPV有效削弱了其感染BmN细胞的能力，并且Bm - SP142降低了BmNPV和BmBDV在家蚕中的增殖效率。此外，Bm - SP142在BmN细胞中的过表达抑制了病毒增殖。