JBC：一种可激活酚氧化酶原系统的模式识别蛋白

甲壳动物拥有比较完善的非特异性免疫系统，当感受到外来微生物入侵以后，会立刻启动相关的免疫级联反应，从而引起细胞吞噬、包囊作用、黑化等免疫反应，这一过程中酚氧化酶（phenoloxidase）起着十分重要的作用。酚氧化酶具有独特的双重催化功能，是生物体内黑色素合成的关键酶，一般以无活性的酶原（prophenoloxidase, proPO）形式存在。酚氧化酶原激活系统在非特异性免疫中作用非常重要，该系统通过模式识别蛋白（pattern recognition proteins，PRPs）识别外来入侵物质，启动免疫级联反应。模式识别蛋白是指存在于动物体内能与脂多糖（LPS），β-1,3-葡聚糖等结合并激活非己识别系统的蛋白。

泰国朱拉隆功大学的研究人员报道了斑节对虾（Penaeus monodon）模式识别蛋白（PmLGBP）在酚氧化酶原激活过程中所起的作用，相关论文发表在 The Journal of Biological Chemistry上。

研究发现被哈维氏弧菌（Vibrio harveyi）侵染24h后，斑节对虾模式识别蛋白在血淋巴中开始表达，酶联免疫吸附试验表明PmLGBP与脂多糖、β-1,3-葡聚糖重组复合体-(r)PmLGBP 的解离常数分别为6.86x10^-7 M和 3.55x10^-7 M。

采用dsRNA干扰介导的基因沉默证实，在活体斑节对虾中敲除模式识别蛋白基因可以显著抑制该蛋白的转录水平，但对其他有免疫功能的基因（如抗菌肽）的表达没有任何影响；进一步研究表明，抑制酚氧化酶原基因（proPO）的表达，可降低PmLGBP的表达，进而使酚氧化酶总活性下降。（生物谷 dulei 编译）

doi:10.1074/jbc.M111.294744
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A pattern recognition protein binds to lipopolysaccharide and beta-1,3-glucan and activates the shrimp prophenoloxidase system

Piti Amparyup, Jantiwan Sutthangkul Walaiporn Charoensapsri， Anchalee Tassanakajon

The prophenoloxidase (proPO) system is activated upon recognition of pathogens by pattern recognition proteins (PRPs), including a lipopolysaccharide and beta-1,3-glucan binding protein (LGBP). However, shrimp LGBPs that are involved in the proPO system have yet to be clarified. Here, we focus on characterizing the role of a Penaeus monodon LGBP (PmLGBP) in the proPO system. We found that PmLGBP transcripts are primarily expressed in the hemocytes and are increased at 24 h after pathogenic bacterium Vibrio harveyi challenge. The binding studies carried out using ELISA indicated that recombinant (r)PmLGBP binds to beta-1,3-glucan and LPS with a dissociation constant of 6.86x10^-7 M and 3.55x10^-7 M, respectively. Furthermore, we found that rPmLGBP could enhance the phenoloxidase (PO) activity of hemocyte suspensions in the presence of LPS or beta-1,3-glucan. Using dsRNA interference-mediated gene silencing assay, we further demonstrated that knockdown of PmLGBP in shrimp in vivo significantly decreased the PmLGBP transcript level but had no effect on the expression of the other immune genes tested, including shrimp antimicrobial peptides (AMPs). However, suppression of proPO expression down-regulated PmLGBP, proPO-activating enzyme (PmPPAE2) and AMPs (Penaeidin and crustin). Such PmLGBP down-regulated shrimp showed a significantly decreased total PO activity. We conclude that PmLGBP functions as a pattern recognition protein for LPS and beta-1,3-glucan in the shrimp proPO activating system.