Chitinases are a group of chitin-degrading enzymes widely distributed in organisms. Chitinases containing two chitin catalytic domains have been widely found in arthropods but their functions remain unclear. In this study, a member of these chitinases from Litopenaeus vannamei (dChi) was identified and functionally studied in the context of immunity. The promoter of dChi contained activator protein 1 (AP-1) binding sites and could be regulated by c-Jun. The recombinant dChi protein showed no bacteriostatic activity in vitro but knockdown of dChi in vivo increased the mortality of shrimp and the bacterial load in tissues after Vibrio parahaemolyticus infection, suggesting that dChi could play a positive role in antibacterial responses. However, silencing of dChi expression significantly decreased the mortality of WSSV-infected shrimp and down-regulated the viral load in tissues, indicating that dChi could facilitate WSSV infection. We further demonstrated that dChi was involved in regulation of the bacterial phagocytosis of hemocytes and expression of a series of immune related transcription factors and antimicrobial peptides. These indicated that the roles of dChi in antibacterial responses and anti-WSSV responses in vivo could result from its regulatory effects on the immune system. Taken together, the current study suggests that double chitin catalytic domain-containing chitinases could be important players in immune regulation in crustaceans.

几丁质酶是一组广泛分布于生物体内的几丁质降解酶。含有两个几丁质催化结构域的几丁质酶已广泛存在于节肢动物中，但其功能尚不清楚。在这项研究中，鉴定了南美白对虾(dChi)的这些几丁质酶的一个成员，并在免疫背景下对其进行了功能研究。dChi 的启动子含有激活蛋白 1 (AP-1) 结合位点，可以被 c-Jun 调控。重组 dChi 蛋白在体外没有表现出抑菌活性，但体内dChi 的敲低增加了虾的死亡率和副溶血性弧菌后组织中的细菌负荷感染，表明 dChi 可以在抗菌反应中发挥积极作用。然而，dChi 表达的沉默显着降低了 WSSV 感染虾的死亡率并下调了组织中的病毒载量，表明 dChi 可以促进 WSSV 感染。我们进一步证明 dChi 参与调节血细胞的细菌吞噬作用以及一系列免疫相关转录因子和抗菌肽的表达。这些表明 dChi 在体内抗菌反应和抗 WSSV 反应中的作用可能源于其对免疫系统的调节作用。综上所述，目前的研究表明，含有双几丁质催化结构域的几丁质酶可能是甲壳类动物免疫调节的重要参与者。