Structure-Function Analysis of Grass Clip Serine Protease Involved in Drosophila Toll Pathway Activation
Structure-Function Analysis of Grass Clip Serine Protease Involved in Drosophila Toll Pathway Activation
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DOI：
10.1074/jbc.m110.182741
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发表时间：
2011-04-08
影响因子：
4.8
通讯作者：
Roussel, Alain
中科院分区：
文献类型：
--
作者：
Kellenberger, Christine;Leone, Philippe;Roussel, Alain
Grass是一种剪切结构域丝氨酸蛋白酶（SP），在果蝇免疫应答过程中参与蛋白水解级联触发Toll通路激活。上位学研究将其定位于顶端蛋白酶ModSP的下游和末端蛋白酶spetzl加工酶的上游。本文报道了草酶原的晶体结构。我们发现Grass显示出相当深的活性位点间隙，与凝血酶和补体级联酶相当。一个关键的独特特征是在一个突起环上的激活位点附近存在一个额外的环（75环）。所有生物化学尝试水解Grass的激活位点都失败了，这强烈表明对该区域的访问受到限制。因此，75环被认为是一种防止自发激活的原始机制。通过比较Grass与已知功能与类似蛋白水解级联反应相关的clip丝氨酸蛋白酶，根据75环的存在和clip结构域的构象，我们可以定义两组。一组（缺乏75环）含有倒数第二蛋白酶，而另一组含有末端蛋白酶。按照这种分类，Grass似乎是一种末端蛋白酶。这一结果是根据记录草功能的遗传数据进行评价的。
Grass is a clip domain serine protease (SP) involved in a proteolytic cascade triggering the Toll pathway activation of Drosophila during an immune response. Epistasic studies position it downstream of the apical protease ModSP and upstream of the terminal protease Spaetzle-processing enzyme. Here, we report the crystal structure of Grass zymogen. We found that Grass displays a rather deep active site cleft comparable with that of proteases of coagulation and complement cascades. A key distinctive feature is the presence of an additional loop (75-loop) in the proximity of the activation site localized on a protruding loop. All biochemical attempts to hydrolyze the activation site of Grass failed, strongly suggesting restricted access to this region. The 75-loop is thus proposed to constitute an original mechanism to prevent spontaneous activation. A comparison of Grass with clip serine proteases of known function involved in analogous proteolytic cascades allowed us to define two groups, according to the presence of the 75-loop and the conformation of the clip domain. One group (devoid of the 75-loop) contains penultimate proteases whereas the other contains terminal proteases. Using this classification, Grass appears to be a terminal protease. This result is evaluated according to the genetic data documenting Grass function.