Crystal structure and assembly of the functional Nanoarchaeum equitans tRNA splicing endonuclease
Crystal structure and assembly of the functional Nanoarchaeum equitans tRNA splicing endonuclease
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DOI：
10.1093/nar/gkp537
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发表时间：
2009-09-01
影响因子：
14.9
通讯作者：
Li, Hong
中科院分区：
文献类型：
--
作者：
Mitchell, Michelle;Xue, Song;Li, Hong
来自马纳米古菌（NEQ）的RNA剪接和加工内切酶属于最近发现的（α β）(2)剪接内切酶家族，它需要两个不同的亚基来进行剪接活性。equitans剪接内切酶包括催化亚基（NEQ205）和结构亚基（NEQ261）。在这里，我们报道了含有这两个亚基的功能NEQ酶在2.1埃的晶体结构，以及单独的NEQ261亚基在2.2埃的晶体结构。该功能酶类似于先前已知的α(2)和α(4)内切酶，但形成异源四聚体：催化亚基（NEQ205）和结构亚基（NEQ261）的两个异源二聚体的二聚体。令人惊讶的是，NEQ261单独形成一个同型二聚体，类似于以前已知的催化亚基的同型二聚体。分离亚基的同型二聚体对异源二聚化有抑制作用，如共价连接的催化同型二聚体在与结构亚基混合时没有RNA裂解活性所示。详细的结构比较揭示了异质二聚化界面比同质二聚化界面更有利，从而提出了通过可用亚基调节酶组装的可能机制。最后，NEQ内切酶独特的柔性活性位点可能解释了其更广泛的底物特异性。
The RNA splicing and processing endonuclease from Nanoarchaeum equitans (NEQ) belongs to the recently identified (alpha beta)(2) family of splicing endonucleases that require two different subunits for splicing activity. N. equitans splicing endonuclease comprises the catalytic subunit (NEQ205) and the structural subunit (NEQ261). Here, we report the crystal structure of the functional NEQ enzyme at 2.1 angstrom containing both subunits, as well as that of the NEQ261 subunit alone at 2.2 angstrom. The functional enzyme resembles previously known alpha(2) and alpha(4) endonucleases but forms a heterotetramer: a dimer of two heterodimers of the catalytic subunit (NEQ205) and the structural subunit (NEQ261). Surprisingly, NEQ261 alone forms a homodimer, similar to the previously known homodimer of the catalytic subunit. The homodimers of isolated subunits are inhibitory to heterodimerization as illustrated by a covalently linked catalytic homodimer that had no RNA cleavage activity upon mixing with the structural subunit. Detailed structural comparison reveals a more favorable hetero- than homodimerization interface, thereby suggesting a possible regulation mechanism of enzyme assembly through available subunits. Finally, the uniquely flexible active site of the NEQ endonuclease provides a possible explanation for its broader substrate specificity.