The complement C1r/C1s, Uegf, and Bmp1 (CUB) domains, which are most exclusively found in extracellular and plasma membrane-related proteins, are involved in various biological processes. In this study, a CUB domain-containing protein (designed as HcCDCP) was cloned and characterized from freshwater pearl mussel (Hyriopsis cumingii). The 2280 bp complete cDNA of the HcCDCP contained a 1002 bp open reading frame, which encoded a protein with 333 amino acids. The predicted HcCDCP protein contained a typical CUB domain and a transmembrane region. The tissue distribution analysis indicated that the HcCDCP was detected in all tissues, and the highest expression was found in hepatopancreas followed by gills. After infection with bacteria (i.e., Staphylococcus aureus and Vibrio parahaemolyticus), virus (white spot syndrome virus) and virus analogs (poly[I:C]), the mRNA level of the HcCDCP was significantly upregulated, suggesting that the HcCDCP might be involved in host immune defense response. The RNA interference revealed that the silencing of the HcCDCP could evidently inhibit the expression levels of lysozyme and tumor necrosis factor. Moreover, the recombinant protein of the CUB domain (rCUB) possessed binding capacity to eight different kinds of bacteria. The polysaccharide binding assay showed that the rCUB specifically bound to lipopolysaccharide, peptidoglycan, and D-mannose. This study provided valuable information for exploring the biological roles of CDCPs in the host defense system of mollusks.

补体C1r / C1s，Uegf和Bmp1（CUB）域（最独特地存在于细胞外和质膜相关蛋白中）涉及各种生物学过程。在这项研究中，从淡水珍珠贻贝（Hyriopsis cumingii）克隆并鉴定了一个含有CUB结构域的蛋白质（设计为HcCDCP）。HcCDCP的2280 bp完整cDNA包含一个1002 bp的开放阅读框，其编码具有333个氨基酸的蛋白质。预测的HcCDCP蛋白包含一个典型的CUB结构域和一个跨膜区域。组织分布分析表明，HcCDCP在所有组织中都检测到了这种蛋白，在肝胰腺中的表达最高，其次是g。在感染细菌（即金黄色葡萄球菌和副溶血性弧菌），病毒（白斑综合症病毒）和病毒类似物（poly [I：C]）后，HcCDCP的mRNA水平显着上调，表明可能参与了HcCDCP在宿主免疫防御反应中。RNA干扰显示HcCDCP沉默可明显抑制溶菌酶和肿瘤坏死因子的表达水平。而且，CUB结构域的重组蛋白（rCUB）具有与八种不同细菌的结合能力。多糖结合试验表明，rCUB与脂多糖，肽聚糖和D-甘露糖特异性结合。这项研究为探索CDCP在软体动物宿主防御系统中的生物学作用提供了有价值的信息。