Ficolin is classified as an immune related protein containing collagen-like and fibrinogen-related domain (FreD). In invertebrates, the functions of fibrinogen-related proteins (FrePs) are of importance to innate immunity. In this study, a FreP in the black tiger shrimp Penaeus monodon was identified and characterized. The PmFreP cDNA is 1,007 bp long with a 921 bp-open reading frame that encodes for 306 amino acids. The deduced PmFreP sequence consists of a signal peptide, an unknown region and the FreD. Phylogenetic analysis showed that PmFreP was clustered with fibrinogen-like proteins in crustaceans which was separated from vertebrate ficolin-like proteins. The deduced fibrinogen-like domain contains four conserved cysteine residues (Cys96, Cys127, Cys249, and Cys262) that are responsible for the formation of disulfide bridges. Gene expression analysis shows that Pmfrep is mainly expressed in the intestine and the expression is significantly upregulated after Vibrio harveyi and white spot syndrome virus (WSSV) challenge. Recombinant PmFreP (rPmFreP) were successfully expressed and purified, and forms a trimeric structure as judged by native-PAGE. Bacterial binding assay showed that the rPmFreD can bind and agglutinate Gram-negative and Gram-positive bacteria in the presence of calcium (Ca²⁺) ions. Moreover, the rPmFreP facilitates the clearance of V. harveyi in vivo. Overall, our results suggested that the PmFreP may serve as pattern recognition receptors implicated in shrimp innate immunity.

Ficolin被分类为包含胶原样和纤维蛋白原相关结构域（FreD）的免疫相关蛋白。在无脊椎动物中，纤维蛋白原相关蛋白（FrePs）的功能对于先天免疫至关重要。在这项研究中，鉴定并鉴定了黑虎虾对虾斑节对虾中的FreP 。的PM FREP的cDNA是1007个碱基长以921 bp的开放阅读框，对于306个氨基酸编码。推导的Pm FreP序列由信号肽，未知区域和FreD组成。系统发育分析表明，PmFreP在甲壳类动物中与纤维蛋白原样蛋白聚集在一起，并与脊椎动物的Ficolin类蛋白分离。推导的类纤维蛋白原结构域包含四个保守的半胱氨酸残基（Cys96，Cys127，Cys249和Cys262），它们负责形成二硫键。基因表达分析表明，Pmfrep主要在肠中表达，在哈维氏弧菌和白斑综合症病毒（WSSV）攻击后该表达明显上调。重组Pm FreP（r Pm FreP）已成功表达和纯化，并形成了三聚体结构（通过native-PAGE判断）。细菌结合试验表明r Pm在钙（Ca ²⁺）离子存在的情况下，FreD可以结合和凝集革兰氏阴性和革兰氏阳性细菌。此外，r Pm FreP促进体内哈氏弧菌的清除。总体而言，我们的结果表明，Pm FreP可能充当模式识别受体，与虾的先天免疫有关。