Antimicrobial peptides (AMPs) play an important role in the host defense system of shrimps. In this study, an Arasin-like peptide, named as LvArasin-like, was identified from the hemocytes of the pacific white shrimp, Litopenaeus vannamei. The complete open reading frame (ORF) of LvArasin-like was 213 bp, encoding 70 amino acid residues with a predicted molecular mass of 5.68 kDa and a theoretical isoelectric point (pI) of 6.73. The predicted peptide consisted of a signal peptide, an N-terminal Pro/Arg-rich domain, and a C-terminal cysteine-rich domain. LvArasin-like expression was most abundant in the gills and was up-regulated in hemocytes after LPS or Poly I:C injection as well as challenges by Vibrio parahaemolyticus or Staphylococcus aureus infection. In the heterologous expression system, LvArasin-like protein (rLvArasin-like) was recombinantly expressed in the forms of a dimer or both a monomer and dimer. The rLvArasin-like could directly bind to gram-positive and gram-negative bacteria and exhibited broad-spectrum antimicrobial activity towards them, with 50 % of minimal inhibitory concentrations (MIC50) of 6.25–50 μM. Moreover, dsRNA-mediated knockdown of LvArasin-like enhanced the susceptibility of shrimp to V. parahaemolyticus. In addition, the transcriptional level of LvArasin-like was downregulated when silencing of the transcription factors LvDorsal and LvRelish using RNAi in vivo. All of these results suggest that LvArasin-like is involved in host defense against bacterial infection. Therefore, it is a potential therapeutic agent for disease control in shrimp aquaculture.

抗菌肽（AMPs）在虾的宿主防御系统中发挥着重要作用。在这项研究中，从太平洋白虾南美白对虾的血细胞中鉴定出一种名为 LvArasin-like 的 Arasin 样肽。LvArasin-like的完整开放阅读框(ORF)为213 bp，编码70个氨基酸残基，预测分子量为5.68 kDa，理论等电点(p I )为6.73。预测的肽由信号肽、N 端富含 Pro/Arg 的结构域和 C 端富含半胱氨酸的结构域组成。LvArasin 样表达在鳃中最为丰富，并且在 LPS 或 Poly I:C 注射以及副溶血性弧菌的攻击后在血细胞中上调或金黄色葡萄球菌感染。在异源表达系统中，LvArasin-like蛋白（rLvArasin-like）以二聚体或单体和二聚体的形式重组表达。rLvArasin-like 可直接与革兰氏阳性和革兰氏阴性细菌结合，并对它们表现出广谱抗菌活性，50% 的最低抑菌浓度 (MIC50) 为 6.25–50 μM。此外，dsRNA 介导的LvArasin 样敲除增强了虾对副溶血性弧菌的敏感性。此外，当转录因子LvDorsal和LvRelish沉默时， LvArasin-like的转录水平被下调在体内使用 RNAi 。所有这些结果表明 LvArasin-like 参与了宿主防御细菌感染的过程。因此，它是虾类水产养殖疾病控制的潜在治疗剂。