DNA錯配修復在保證DNA復制的忠實性方面發(fā)揮重要作用，Multα是真核生物錯配修復過程中的重要蛋白質(zhì),，它和其它蛋白質(zhì)的相互作用可能由其構(gòu)象變化所調(diào)節(jié),。Sacho等人用原子力顯微鏡直接觀察到了Mutlα的構(gòu)象變化,，該研究結(jié)果以封面文章的形式發(fā)表在1月18日的《分子細胞》上,。
Multα是原核生物中Mult的同源蛋白質(zhì),，是由Mlh1和Pms2（酵母中為Pms1）構(gòu)成的異源雙聚體,，每個單體均包括一個C末端二聚體結(jié)構(gòu)域和N末端ATP酶結(jié)構(gòu)域,。Mutl及其同源體屬于GHL ATP酶家族,，該家族的蛋白質(zhì)會由于ATP的結(jié)合或（和）水解發(fā)生構(gòu)象變化,，這和細胞中信號轉(zhuǎn)導途徑相關(guān),。
以往研究表明ATP的結(jié)合可能導致Mutlα的構(gòu)象變化，并由此調(diào)節(jié)其于其它蛋白質(zhì)的相互作用,，激活下游的蛋白因子啟動DNA錯配修復過程,，但這些推斷僅源于對分離的蛋白質(zhì)部分結(jié)構(gòu)域的晶體衍射和尺寸排阻色譜以及間接的生物化學分析,，缺乏直接的證據(jù),。
來自美國北卡羅來納大學等多家研究機構(gòu)的科學家用原子力顯微鏡觀測了酵母和人類Multα整個分子的構(gòu)象，結(jié)果發(fā)現(xiàn)二者均存在四種構(gòu)象,，ATP和ADP的結(jié)合均能夠改變其構(gòu)象,。用部分水解等生物化學分析方法,，發(fā)現(xiàn)在溶液中ATP的結(jié)合也能夠改變Multα的構(gòu)象,。該構(gòu)象變化涉及大量二級結(jié)構(gòu)的改變,。
為檢測Multα構(gòu)象變化是否必需ATP的水解，研究人員進一步對缺乏ATP水解酶活性的Multα突變體進行研究,，并且用不可水解的ATP同源物AMPPNP做比較研究,，結(jié)果表明ATP構(gòu)象變化是由ATP的結(jié)合所引起,，而非ATP水解。
據(jù)推測,，Multα的四種構(gòu)想可能和ATP的結(jié)合,、水解和釋放過程相關(guān)，Multα通過構(gòu)象變化暴露或隱藏部分結(jié)構(gòu),，從而改變同其它蛋白質(zhì)間的相互作用,。（科學網(wǎng) 穆宏平/編譯）
（《分子細胞》（Molecular Cell）,，Vol 29, 112-121, 18 January 2008,，Elizabeth J. Sacho, Dorothy A. Erie）
生物谷推薦英文原文：
Molecular Cell, Vol 29, 112-121, 18 January 2008
Article
Direct Visualization of Asymmetric Adenine Nucleotide-Induced Conformational Changes in MutLα
Elizabeth J. Sacho,1 Farid A. Kadyrov,4 Paul Modrich,3,4 Thomas A. Kunkel,5 and Dorothy A. Erie1,2,
1 Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
2 Curriculum in Applied and Materials Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
3 Howard Hughes Medical Institute, Duke University Medical Center, Durham, NC 27710, USA
4 Department of Biochemistry, Duke University Medical Center, Durham, NC 27710, USA
5 Laboratory of Molecular Genetics, National Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, NC 27709, USA
Corresponding author
Dorothy A. Erie
[email protected]
MutLα, the heterodimeric eukaryotic MutL homolog, is required for DNA mismatch repair (MMR) in vivo. It has been suggested that conformational changes, modulated by adenine nucleotides, mediate the interactions of MutLα with other proteins in the MMR pathway, coordinating the recognition of DNA mismatches by MutSα and the activation of MutLα with the downstream events that lead to repair. Thus far, the only evidence for these conformational changes has come from X-ray crystallography of isolated domains, indirect biochemical analyses, and comparison to other members of the GHL ATPase family to which MutLα belongs. Using atomic force microscopy (AFM), coupled with biochemical techniques, we demonstrate that adenine nucleotides induce large asymmetric conformational changes in full-length yeast and human MutLα and that these changes are associated with significant increases in secondary structure. These data reveal an ATPase cycle in which sequential nucleotide binding, hydrolysis, and release modulate the conformational states of MutLα.
