青年發(fā)病的成年型糖尿?。∕ODY1）是一種罕見的糖尿病,，這種疾病患者的HNF-4α蛋白發(fā)生了可遺傳的突變,。在肝臟和胰腺中HNF-4α負責控制基因表達,，按照機體需要啟動或關(guān)閉基因。現(xiàn)在,，研究人員首次明確了HNF-4α蛋白的完整三維結(jié)構(gòu),，并且在該蛋白中發(fā)現(xiàn)了新的結(jié)合域，文章發(fā)表在3月13日的Nature雜志上,。這項研究不僅有助于人們進一步了解HNF-4α的作用機制,，還為人們提供了開發(fā)MODY1治療藥物的新靶標。
HNF-4α蛋白三維結(jié)構(gòu)及與DNA的作用圖
“此前,，HNF-4α及相關(guān)核受體的結(jié)構(gòu)研究都只是針對蛋白的一部分,，”文章的資深作者，Sanford-Burnham糖尿病和肥胖研究中心的Fraydoon Rastinejad教授說,。“許多人認為這些蛋白不同結(jié)構(gòu)域之間是松散無關(guān)聯(lián)的,，因此只對HNF-4α的不同片段進行研究。但我們發(fā)現(xiàn)事實并非如此,，HNF-4α結(jié)構(gòu)域之間高度有序而且相互關(guān)聯(lián),，這種組織形式將幫助我們進一步理解MODY1，并推動相關(guān)治療藥物的開發(fā),。”
給MODY1的啟示
Rastinejad的研究告訴人們,，為何改變HNF-4α蛋白結(jié)構(gòu)的可遺傳突變會有如此大的破壞力。這種會引發(fā)MODY1的突變,，通常出現(xiàn)在HNF-4α蛋白的一個特殊小區(qū)域中,，該區(qū)域距離DNA結(jié)合域還很遠。Rastinejad及其團隊發(fā)現(xiàn),，盡管相距甚遠,，該突變還是能將信號傳遞到DNA結(jié)合域，導(dǎo)致HNF-4α發(fā)生功能故障,，而引發(fā)MODY1,。
研究人員還在HNF-4α蛋白中發(fā)現(xiàn)了可以作為藥物靶標的新區(qū)域。與其他核受體類似,，HNF-4α具有結(jié)合天然信號分子的區(qū)域,，這些區(qū)域可以作為合成藥物的靶標。不過這項研究顯示,，該蛋白的其他結(jié)構(gòu)域也可以作為藥物靶標,。這是因為HNF-4α的不同結(jié)構(gòu)域之間存在相互交流，研究人員認為結(jié)合在遠端結(jié)構(gòu)域的藥物,，仍然可以影響該蛋白與DNA的結(jié)合,。
“我們正在與同事合作篩選大型化合物文庫（約含有三十萬種化合物），來尋找分子與我們新發(fā)現(xiàn)的區(qū)域結(jié)合，”Rastinejad說,。“這種分子將有望使MODY1患者的HNF-4α恢復(fù)DNA結(jié)合能力,。這樣的話，即使無法修復(fù)突變,，我們?nèi)耘f可以通過藥物,，挽救該受體與DNA緊密結(jié)合的能力。”
核受體的新認識
HNF-4α屬于一種特殊的蛋白類型,，被稱為核受體,。這種蛋白在細胞中與DNA結(jié)合，根據(jù)外界信號控制著無數(shù)基因的啟動和關(guān)閉,。核受體是理想的藥物靶標,，它的一部分負責結(jié)合DNA，而另一個部分具有與信號分子結(jié)合的區(qū)域,，與這些區(qū)域結(jié)合的藥物,，就可以控制核受體從而影響基因表達。
迄今為止,，許多研究人員還認為絕大多數(shù)核受體就像一串穿線的珠子,。每個珠子（蛋白結(jié)構(gòu)域）都有一個功能，但穿在彼此之間的線是松散的?，F(xiàn)在,，Rastinejad及其團隊指出，HNF-4α結(jié)構(gòu)域之間其實是協(xié)調(diào)有序的,，一個接收到信號的結(jié)構(gòu)域能夠?qū)⑿盘杺鬏數(shù)降鞍椎倪h端區(qū)域,。Rastinejad指出，這些結(jié)構(gòu)域之間存在彼此交流,。
HNF-4α主要存在于肝臟和胰腺細胞,，它依據(jù)器官的需要調(diào)節(jié)基因的活性。HNF-4α參與控制著碳水化合物代謝,、葡萄糖調(diào)控,、胰島素合成以及許多其他的重要過程。換句話說,，全靠HNF-4α肝臟和胰臟才能實現(xiàn)各自的功能,。(生物谷Bioon.com)
doi: 10.1038/nature11966
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Multidomain integration in the structure of the HNF-4α nuclear receptor complex.
Chandra V, Huang P, Potluri N, Wu D, Kim Y, Rastinejad F.
The hepatocyte nuclear factor 4α (HNF-4α; also known as NR2A1) is a member of the nuclear receptor (NR) family of transcription factors, which have conserved DNA-binding domains and ligand-binding domains. HNF-4α is the most abundant DNA-binding protein in the liver, where some 40% of the actively transcribed genes have a HNF-4α response element. These regulated genes are largely involved in the hepatic gluconeogenic program and lipid metabolism. In the pancreas HNF-4α is also a master regulator, controlling an estimated 11% of islet genes. HNF-4α protein mutations are linked to maturity-onset diabetes of the young, type 1 (MODY1) and hyperinsulinaemic hypoglycaemia. Previous structural analyses of NRs, although productive in elucidating the structure of individual domains, have lagged behind in revealing the connectivity patterns of NR domains. Here we describe the 2.9?? crystal structure of the multidomain human HNF-4α homodimer bound to its DNA response element and coactivator-derived peptides. A convergence zone connects multiple receptor domains in an asymmetric fashion, joining distinct elements from each monomer. An arginine target of PRMT1 methylation protrudes directly into this convergence zone and sustains its integrity. A serine target of protein kinase C is also responsible for maintaining domain-domain interactions. These post-translational modifications lead to changes in DNA binding by communicating through the tightly connected surfaces of the quaternary fold. We find that some MODY1 mutations, positioned on the ligand-binding domain and hinge regions of the receptor, compromise DNA binding at a distance by communicating through the interjunctional surfaces of the complex. The overall domain representation of the HNF-4α homodimer is different from that of the PPAR-γ-RXR-α heterodimer, even when both NR complexes are assembled on the same DNA element. Our findings suggest that unique quaternary folds and interdomain connections in NRs could be exploited by small-molecule allosteric modulators that affect distal functions in these polypeptides.
