我們體內(nèi)細胞眾多的基因中,，只有那些表達的基因使我們成為現(xiàn)在這個樣子。特定的蛋白通過結(jié)合DNA上的關(guān)鍵位點——包含遺傳信息的核酸,，調(diào)節(jié)基因表達,。
這些蛋白是怎樣識別特定結(jié)合位點的,？蛋白結(jié)構(gòu)和DNA結(jié)構(gòu)的改變,，有時是結(jié)合位點內(nèi)的DNA紐結(jié)或急劇彎曲，使得DNA－蛋白緊密結(jié)合,。
研究人員認為DNA在這種遺傳相互作用中是被動的一方,。但是由伊利諾斯州大學生物物理學副教授Anjum Ansari發(fā)現(xiàn)，DNA并不是所想象的完全被動的,。
為了對蛋白－DNA結(jié)合時發(fā)生的結(jié)構(gòu)變化進行實時檢測,，Ansari及其同事利用一種細菌來源的檢測蛋白，和持續(xù)一百億分之一秒的激光脈沖加熱,、攪亂蛋白－DNA復合物,，觀察結(jié)合蛋白的動力學改變情況。這是首次利用激光脈沖升溫光源法（laser temperature-jump technique,，生物通編者譯）研究蛋白－DNA復合物動力學,。
Ansari說：“止流（stopped-flow）技術(shù)可以捕獲毫秒時間內(nèi)出現(xiàn)的生物分子的動力學變化，此次研究的目的是將時長范圍縮小到微秒級別以下,。”這種技術(shù)與止流測量方法結(jié)合,，可直接觀測DNA與蛋白結(jié)合過程。
Ansari發(fā)現(xiàn)DNA的結(jié)合時間級別與先前報道的一個堿基對瞬時降解的時間級別相似,。推測,，DNA可以自行的彎曲或者打結(jié),，蛋白識別彎曲的DNA結(jié)構(gòu)并與之緊密結(jié)合。
Ansari及其同事的結(jié)論稍微背離傳統(tǒng)教條,，傳統(tǒng)觀點認為是蛋白結(jié)合DNA,，而Ansari等認為DNA“彎曲特性”（bendability）指導蛋白到特定的DNA位點。
Ansari說這個新發(fā)現(xiàn)有助于研究蛋白識別特異結(jié)合位點的機制,，為研發(fā)蛋白結(jié)合DNA特異位點的藥物和以基因為基礎(chǔ)的治療方法提供一臂之力,。
英文原文：
Gene-Bender Proteins May Sway to DNA
Among the many genes packed into each cell of our body, those that get turned on, or expressed, are the ones that make us who we are. Certain proteins do the job of regulating gene expression by clasping onto key spots of DNA -- the nucleic acid that contains the genetic instructions.
How does the protein recognize a particular binding site? Structural changes in both the protein and DNA, sometimes with the DNA within the complex kinked or sharply bent, allow for the specific contacts needed for a tight DNA-protein fit.
Scientists think DNA is largely passive in this genetic tango. But new findings by Anjum Ansari, associate professor of biophysics at the University of Illinois at Chicago, suggest DNA may not be the wallflower that many had assumed.
To follow in real time the structural changes that accompany protein-DNA binding, Ansari and her UIC colleagues used a test protein from bacteria and applied a laser pulse lasting about 10 billionths of a second to heat up and disturb the protein-DNA complex. They watched the dynamics of the bound DNA in response to this perturbation.
Ansari's group was the first to apply the laser temperature-jump technique to study the dynamics of a protein-DNA complex.
The studies were done in collaboration with Donald Crothers, Sterling Professor Emeritus of chemistry at Yale University, who examined the protein-DNA interaction with the more traditional stopped-flow technique.
"While stopped-flow technique can capture dynamics of biomolecules occurring on millisecond time-scales or longer, the goal of this study was to extend the time-resolution down to sub-microseconds. It gave us a new time window on probing protein-DNA interactions," Ansari said.
That broader time window, obtained in combination with the stopped-flow measurements, provided the first direct observation of DNA bending when bound to a DNA-bending protein.
"We found that the time-scales on which DNA was bending were very similar to previously reported time-scales on which individual base-pairs that hold the two DNA strands together were transiently breaking. That led us to conclude that the DNA is able to bend or kink on its own, at weak points created by the transient opening of base-pairs, and that the protein recognizes and binds tightly to the bent DNA conformation."
Conclusions by Ansari and her colleagues deviate slightly from the conventional dogma that it is the protein that bends the DNA. She said the results raise important questions about the role that the DNA "bendability" plays in guiding the correct bending protein to the appropriate site on the DNA.
Ansari said the research adds to the basic understanding of how proteins recognize a specific binding site.
"Gaining better insights into protein-DNA interactions that control all aspects of gene regulation may prove useful for rational design of drugs to target specific sites on the DNA, whereby one can ultimately develop better gene-based therapies," she said.
The findings appear in the Dec. 5 issue of the Proceedings of the National Academy of Sciences. Serguei Kuznetsov, research assistant professor of physics at UIC, is first author on the paper; Ansari and Crothers are corresponding authors. Other co-authors include graduate students Paula Vivas, working with Ansari at UIC, and Sawako Sugimura, working with Crothers at Yale.
The research was supported by grants from the National Science Foundation, the American Chemical Society Petroleum Research Fund and the National Institutes of Health.
