来自布兰迪斯大学（Brandeis University），霍德华休斯医学院的研究人员揭开了酶这一在细胞活动中扮演着重要角色的成分的生活秘密，他们利用一种成熟的新技术实时捕捉到了一种关键酶变换形状的图像，上演了一幕酶动力学舞蹈的精彩剧目。这一研究成果公布在11月18日的Nature杂志上。
这一研究在布兰迪斯大学完成，这是一所私立小型大学，虽然只有几十年的历史，在美国教育界却颇有地位，被誉为“全美最年青的主要研究院大学”。这所每年用在每名学生身上的经费高达29,500多美元的高等学府，以理科最为出色，生物化学(全美排第11)、物理(全美排第30)、化学(全美排第38)及生物，举国知名，其他学科，如计算机科学、英文、历史、政治科学和经济，也备受赞扬。领导完成这项研究的就是布兰迪斯大学的霍德华休斯医学院研究员Dorothee Kern博士。
Kern和她的同事通过实时捕捉酶动力学特征，发现这些蛋白并不如之前生命科学研究人员认为的那样，直到催化事件发生才实质性的激活，而是在其催化时——底物结合上来之前就完成了一段动力学变化。这一研究的重要性在于能说明酶在完成各项重要的催化工作之前的细小变化。
在Kern等人的这两篇文章中，研究人员实际上获得了一种酶在底物不存在的情况下，形状或者构造的改变的整体图像，Kern表示，“这确实是一种形态转变”，早期的研究只能获得酶固化后的snapshots，它们真实的细微变化并不清楚。
这一为期三年的研究是一项突破，帮助研究人员更加深入了解了酶的动力学特征，Kern等人多年来一直致力于捕捉酶如何移动，以及如何改变形状，她在核磁共振（nuclear magnetic resonance，NMR）技术应用方面取得了许多经验，这种技术能检测到一个蛋白中个体原子的运动。但是在这项研究中，研究人员需要更多的实验技术帮助他们不仅获得关键蛋白的运动情况，还有蛋白的结构变化情况。他们需要了解这种短暂的，罕见的酶的形状——这对于理解以及设计药物至关重要。
原始出处:
Nature 450, 838-844 (6 December 2007) | doi:10.1038/nature06410; Received 14 April 2007; Accepted 26 October 2007; Published online 18 November 2007
Intrinsic motions along an enzymatic reaction trajectory
Katherine A. Henzler-Wildman1, Vu Thai1, Ming Lei1, Maria Ott3, Magnus Wolf-Watz1,6, Tim Fenn2,6, Ed Pozharski2,6, Mark A. Wilson2,6, Gregory A. Petsko2, Martin Karplus4,5, Christian G. Hübner3,6 & Dorothee Kern1
Department of Biochemistry and Howard Hughes Medical Institute,
Department of Biochemistry, Brandeis University, Waltham, Massachusetts 02454, USA
Institute of Physics, Martin Luther-University Halle-Wittenberg, D-06120 Halle, Germany
Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA
Laboratoire de Chimie Biophysique, ISIS, Université Louis Pasteur, F-67000 Strasbourg, France
Present addresses: University of Umeå, Department of Chemistry, SE-90187 Umeå, Sweden (M.W.-W.); Departments of Molecular and Cellular Physiology and Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA (T.F.); Department of Pharmaceutical Sciences, University of Maryland, Baltimore, Maryland 21201, USA (E.P.); Department of Biochemistry and the Redox Biology Center, University of Nebraska, Lincoln, Nebraska 68588, USA (M.A.W.); University at Lübeck, Institute of Physics, 23538 Lübeck, Germany (C.G.H.).
Correspondence to: Christian G. Hübner3,6Dorothee Kern1 Correspondence and requests for materials should be addressed to D.K. (Email: dkern@brandeis.edu) or C.G.H. (Email: huebner@physik.uni-luebeck.de).
The mechanisms by which enzymes achieve extraordinary rate acceleration and specificity have long been of key interest in biochemistry. It is generally recognized that substrate binding coupled to conformational changes of the substrate–enzyme complex aligns the reactive groups in an optimal environment for efficient chemistry. Although chemical mechanisms have been elucidated for many enzymes, the question of how enzymes achieve the catalytically competent state has only recently become approachable by experiment and computation. Here we show crystallographic evidence for conformational substates along the trajectory towards the catalytically competent 'closed' state in the ligand-free form of the enzyme adenylate kinase. Molecular dynamics simulations indicate that these partially closed conformations are sampled in nanoseconds, whereas nuclear magnetic resonance and single-molecule fluorescence resonance energy transfer reveal rare sampling of a fully closed conformation occurring on the microsecond-to-millisecond timescale. Thus, the larger-scale motions in substrate-free adenylate kinase are not random, but preferentially follow the pathways that create the configuration capable of proficient chemistry. Such preferred directionality, encoded in the fold, may contribute to catalysis in many enzymes.
