Ultrafast ligand rebinding in the heme domain of the oxygen sensors FixL and Dos:: General regulatory implications for heme-based sensors
Ultrafast ligand rebinding in the heme domain of the oxygen sensors FixL and Dos:: General regulatory implications for heme-based sensors
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DOI：
10.1073/pnas.192311699
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发表时间：
2002-10-01
影响因子：
11.1
通讯作者：
Vos, MH
中科院分区：
文献类型：
--
作者：
Liebl, U;Bouzhir-Sima, L;Vos, MH
基于血红素的氧传感器是配体特异性双组分调控系统的一部分，具有相对较低的氧亲和力和低的氧结合率。为了深入了解这些特征背后的动力学方面以及来自血红素敏感域的信号转导的配体特异性，我们使用飞秒光谱研究了来自缓生根瘤菌的氧传感器FixL(FixLH)和来自大肠杆菌的DOS(DOSH)的血红素域的配体动力学。FixLh与不同配体的血红素配位以及相应的基态血红素光谱与肌红蛋白(Mb)相似。光解后，以CO和NO为配体的FixLh和Mb的激发态性质和配体重结合动力学性质相似。与Mb相比，配体光解后FixLh的瞬时光谱与基态差分光谱相比发生了扭曲，表明血红素环境相对于未连接状态有所不同。这种扭曲对于O-2来说尤其明显。引人注目的是，血红素-氧-2的重组发生的效率对于血红素蛋白来说是前所未有的，大约为5ps，大约90%的游离氧-2。对于DOSH-O-2，它显示出与FixLH 60%的序列相似性，但其中信号检测和传输可能非常不同，发现了类似的快速重组，具有更高的产率。总而言之，这些结果表明，在这些传感器中，血红素口袋起到了配体特异性陷阱的作用。结合基于血红素的NO和CO传感器的最新研究，讨论了基于血红素的配体传感器的功能的一般含义。
Heme-based oxygen sensors are part of ligand-specific two-component regulatory systems, which have both a relatively low oxygen affinity and a low oxygen-binding rate. To get insight into the dynamical aspects underlying these features and the ligand specificity of the signal transduction from the heme sensor domain, we used femtosecond spectroscopy to study ligand dynamics in the heme domains of the oxygen sensors FixL from Bradyrhizobium japonicum (FixLH) and Dos from Escherichia coli (DosH). The heme coordination with different ligands and the corresponding ground-state heme spectra of FixLH are similar to myoglobin (Mb). After photodissociation, the excited-state properties and ligand-rebinding kinetics are qualitatively similar for FixLH and Mb for CO and NO as ligands. in contrast to Mb, the transient spectra of FixLH after photodissociation of ligands are distorted compared with the ground-state difference spectra, indicating differences in the heme environment with respect to the unliganded state. This distortion is particularly marked for O-2. Strikingly, heme-O-2 recombination occurs with efficiency unprecedented for heme proteins, in approximate to5 ps for approximate to90% of the dissociated O-2. For DosH-O-2, which shows 60% sequence similarity to FixLH, but where signal detection and transmission presumably are quite different, a similarly fast recombination was found with an even higher yield. Altogether these results indicate that in these sensors the heme pocket acts as a ligand-specific trap. The general implications for the functioning of heme-based ligand sensors are discussed in the light of recent studies on heme-based NO and CO sensors.