Pinakoulaki Eftychia, Yoshimura Hideaki, Daskalakis Vangelis, Yoshioka Shiro, Aono Shigetoshi, Varotsis Constantinos
Department of Chemistry, University of Crete, Heraklion, 710 03 Voutes, Crete, Greece.
Proc Natl Acad Sci U S A. 2006 Oct 3;103(40):14796-801. doi: 10.1073/pnas.0604248103. Epub 2006 Sep 26.
We have identified a ligand (CO) accommodation cavity in the signal transducer sensor protein HemAT (heme-based aerotactic transducer) that allows us to gain single-molecule insights into the mechanism of gas sensor proteins. Specific mutations that are distal and proximal to the heme were designed to perturb the electrostatic field near the ligand that is bound to the heme and near the accommodated ligand in the cavity. We report the detection of a second site in heme proteins in which the exogenous ligand is accommodated in an internal cavity. The conformational gate that directs the ligand-migration pathway from the distal to the proximal site of the heme, where the ligand is trapped, has been identified. The data provide evidence that the heme pocket is the specific ligand trap and suggest that the regulatory mechanism may be tackled starting from more than one position in the protein. Based on the results, we propose a dynamic coupling between the two distinct binding sites as the underlying allosteric mechanism for gas recognition/discrimination that triggers a conformational switch for signaling by the oxygen sensor protein HemAT.
我们在信号转导传感器蛋白HemAT（基于血红素的趋氧性转导器）中确定了一个配体（CO）容纳腔，这使我们能够在单分子水平上深入了解气体传感器蛋白的作用机制。设计了位于血红素远端和近端的特定突变，以扰乱与血红素结合的配体附近以及腔内容纳的配体附近的静电场。我们报告了在血红素蛋白中检测到第二个位点，外源配体在该位点被容纳在内部腔中。已经确定了引导配体从血红素远端迁移到近端位点（配体被困于此）的构象门。数据表明血红素口袋是特定的配体陷阱，并表明调节机制可能从蛋白质中的多个位置入手。基于这些结果，我们提出两个不同结合位点之间的动态偶联是气体识别/区分的潜在变构机制，它触发了氧传感器蛋白HemAT进行信号传导的构象转换。
