Masquerade (Mas) is a secreted trypsin-like serine protease (SPs) and involved in immune response in some arthropods. However, according to previous studies, Mas presents different functional activities. In the present study, the functional mechanisms of Mas in crayfish Procambarus clarkii immune defense were studied. A fragment cDNA sequence of PcMas was identified and characterized. From the structural analysis, it contains a trypsin-like serine protease domain. The highest expression level of PcMas was detected in hepatopancreas. The infection of A. hydrophila could induce the expression of PcMas, while the WSSV infection did not cause changes in the expression of PcMas. Through the prokaryotic expression system, the PcMas protein was expressed in E. coli. It was verified that PcMas can bind to bacteria in vitro and inhibit the growth of the bacteria. By dsRNA interference with the expression of PcMas, the decrease expression of PcMas led to a decrease in the activity of phenoloxidase in hemolymph and an increase of mortality caused by A. hydrophila infection. The injection of recombinant protein can enhance the activity of phenoloxidase and reduce mortality caused by A. hydrophila infections. Therefore, the present study confirmed that PcMas could improve the body's immune response to eliminate bacterial pathogens by binding with bacteria and activating the prophenoloxidase system. The results will enrich the molecular mechanisms of crustaceans immune defense.

假面舞会 (Mas) 是一种分泌的胰蛋白酶样丝氨酸蛋白酶 (SPs)，参与某些节肢动物的免疫反应。然而，根据先前的研究，Mas 呈现出不同的功能活动。在本研究中，研究了Mas在小龙虾Procambarus clarkii免疫防御中的功能机制。鉴定和表征了Pc Mas的片段 cDNA 序列。从结构分析来看，它含有一个胰蛋白酶样丝氨酸蛋白酶结构域。在肝胰腺中检测到Pc Mas的最高表达水平。A.hydrophila感染可诱导Pc Mas 表达，而 WSSV 感染不引起PcMas表达变化. 通过原核表达系统，Pc Mas蛋白在大肠杆菌中表达。经证实，Pc Mas可以在体外与细菌结合，抑制细菌的生长。通过dsRNA干扰Pc Mas的表达，Pc Mas的表达降低导致血淋巴中酚氧化酶活性降低，导致A.hydrophila感染的死亡率增加。注射重组蛋白可以增强酚氧化酶的活性，降低嗜水曲霉感染引起的死亡率。因此，本研究证实PcMas可以通过与细菌结合并激活酚氧化酶原系统来提高人体的免疫反应以消除细菌病原体。研究结果将丰富甲壳类动物免疫防御的分子机制。