甲殼動(dòng)物擁有比較完善的非特異性免疫系統(tǒng),，當(dāng)感受到外來微生物入侵以后，會(huì)立刻啟動(dòng)相關(guān)的免疫級聯(lián)反應(yīng),，從而引起細(xì)胞吞噬,、包囊作用、黑化等免疫反應(yīng),，這一過程中酚氧化酶（phenoloxidase）起著十分重要的作用,。酚氧化酶具有獨(dú)特的雙重催化功能，是生物體內(nèi)黑色素合成的關(guān)鍵酶,，一般以無活性的酶原（prophenoloxidase, proPO）形式存在,。酚氧化酶原激活系統(tǒng)在非特異性免疫中作用非常重要，該系統(tǒng)通過模式識別蛋白（pattern recognition proteins,，PRPs）識別外來入侵物質(zhì),，啟動(dòng)免疫級聯(lián)反應(yīng)。模式識別蛋白是指存在于動(dòng)物體內(nèi)能與脂多糖（LPS）,，β-1,3-葡聚糖等結(jié)合并激活非己識別系統(tǒng)的蛋白,。
泰國朱拉隆功大學(xué)的研究人員報(bào)道了斑節(jié)對蝦（Penaeus monodon）模式識別蛋白（PmLGBP）在酚氧化酶原激活過程中所起的作用，相關(guān)論文發(fā)表在 The Journal of Biological Chemistry上,。
研究發(fā)現(xiàn)被哈維氏弧菌（Vibrio harveyi）侵染24h后,，斑節(jié)對蝦模式識別蛋白在血淋巴中開始表達(dá)，酶聯(lián)免疫吸附試驗(yàn)表明PmLGBP與脂多糖,、β-1,3-葡聚糖重組復(fù)合體-(r)PmLGBP 的解離常數(shù)分別為6.86x10-7 M和 3.55x10-7 M,。
采用dsRNA干擾介導(dǎo)的基因沉默證實(shí)，在活體斑節(jié)對蝦中敲除模式識別蛋白基因可以顯著抑制該蛋白的轉(zhuǎn)錄水平,，但對其他有免疫功能的基因（如抗菌肽）的表達(dá)沒有任何影響,；進(jìn)一步研究表明，抑制酚氧化酶原基因（proPO）的表達(dá),，可降低PmLGBP的表達(dá),，進(jìn)而使酚氧化酶總活性下降。（生物谷 dulei 編譯）
doi:10.1074/jbc.M111.294744
PMC:
PMID:
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.
