Dos, a heme-binding PAS protein from Escherichia coli, is a direct oxygen sensor
Dos, a heme-binding PAS protein from Escherichia coli, is a direct oxygen sensor
复制标题
DOI：
10.1021/bi991911s
复制
发表时间：
2000-03-14
期刊：
影响因子：
2.9
通讯作者：
Gilles-Gonzalez, MA
中科院分区：
文献类型：
--
作者：
Delgado-Nixon, VM;Gonzalez, G;Gilles-Gonzalez, MA
在大肠杆菌中发现了一种氧气（O₂）的直接传感器——Dos蛋白。此前，已知通过直接且可逆的结合对氧气作出反应的唯一生物传感器是根瘤菌的FixL蛋白。Dos中的一个血红素结合区域与FixL蛋白的氧气感应PAS结构域有60%的同源性，但Dos的其余部分与FixL并不相似。具体而言，Dos的C末端结构域被认为是与其血红素结合结构域偶联的调节伙伴，它不是一种组氨酸激酶，而更类似于一种磷酸二酯酶。Dos的吸收光谱表明，血红素铁的两个轴向位置都与蛋白质的侧链配位。然而，氧气和一氧化碳与Dos结合的解离常数（Kd）分别为13μM和10μM，这表明对一氧化碳结合有很强的选择性。氧气（3 mM⁻¹ s⁻¹）、一氧化碳（1 mM⁻¹ s⁻¹）甚至一氧化氮（2 mM⁻¹ s⁻¹）的结合速率常数都极低且非常相似。Dos中血红素铁上的一种内源性配体（可能是Met 95）的置换会引发一种构象变化，从而改变酶结构域的活性。这种感应机制不同于FixL的机制，但类似于深红红螺菌的一氧化碳传感器CooA的机制。总体而言，这些结果为PAS结构域蛋白的一个血红素结合亚群提供了证据，其工作范围、信号传导机制和调节伙伴可能有很大差异。
A direct sensor Of O-2, the Dos protein, has been found in Escherichia coli. Previously, the only biological sensors known to respond to O-2 by direct and reversible binding, were the FixL proteins of Rhizobia. A heme-binding region in Dos is 60% homologous to the O-2-sensing PAS domain of the FixL protein, but the remainder of Dos does not resemble FixL. Specifically, the C-terminal domain of Dos, presumed to be a regulatory partner that couples to its heme-binding domain, is not a histidine kinase but more closely resembles a phosphodiesterase. The absorption spectra of Dos indicate that both axial positions of the heme iron are coordinated to side chains of the protein. Nevertheless, O-2 and CO bind to Dos with K-d values of 13 and 10 muM, respectively, indicating a strong discrimination against CO binding. Association rate constants for binding Of O-2 (3 mM(-1) s(-1)), CO (1 mM(-1) s(-1)) and even NO (2 mM(-1) s(-1)) are extraordinarily low and very similar. Displacement of an endogenous ligand, probably Met 95, from the heme iron in Dos triggers a conformational change that alters the activity of the enzymatic domain. This sensing mechanism differs from that of FixL but resembles that of the CO sensor CooA of Rhodospirillum rubrum. Overall the results provide evidence for a heme-binding subgroup of PAS-domain proteins whose working range, signaling mechanisms, and regulatory partners can vary considerably.