Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119991, Russia.
Biochemistry (Mosc). 2020 Dec;85(12):1603-1612. doi: 10.1134/S0006297920120123.
Cytochrome bd-I is a terminal oxidase of the Escherichia coli respiratory chain. This integral membrane protein contains three redox-active prosthetic groups (hemes b, b, and d) and couples the electron transfer from quinol to molecular oxygen to the generation of proton motive force, as one of its important physiological functions. The study was aimed at examining the effect of the membrane environment on the ligand-binding properties of cytochrome bd-I by absorption spectroscopy. The membrane environment was found to modulate the ligand-binding characteristics of the hemoprotein in both oxidized and reduced states. Absorption changes upon the addition of exogenous ligands, such as cyanide or carbon monoxide (CO), to the detergent-solubilized enzyme were much more significant and heterogeneous than those observed with the membrane-bound enzyme. In the native membranes, both cyanide and CO interacted mainly with heme d. An additional ligand-binding site (heme b) appeared in the isolated enzyme, as was evidenced by more pronounced changes in the absorption in the Soret band. This additional reactivity could also be detected after treatment of E. coli membranes with a detergent. The observed effect did not result from the enzyme denaturation, since reconstitution of the isolated enzyme into azolectin liposomes restored the ligand-binding pattern close to that observed for the intact membranes.
细胞色素 bd-I 是大肠杆菌呼吸链的末端氧化酶。这种整合膜蛋白含有三个氧化还原活性的辅基（血红素 b、b 和 d），其重要的生理功能之一是将来自醌的电子传递与分子氧偶联，以产生质子动力势。本研究旨在通过吸收光谱研究膜环境对细胞色素 bd-I 配体结合特性的影响。研究发现，膜环境在氧化和还原状态下均调节血红素蛋白的配体结合特性。与膜结合酶相比，去污剂溶解的酶中外源配体（如氰化物或一氧化碳（CO））添加后引起的吸收变化更为显著和不均匀。在天然膜中，氰化物和 CO 主要与血红素 d 相互作用。在分离的酶中出现了一个额外的配体结合位点（血红素 b），这可以通过 Soret 带吸收的更明显变化来证明。在用去污剂处理大肠杆菌膜后也可以检测到这种额外的反应性。观察到的效应不是由于酶变性引起的，因为将分离的酶重新组装到藻朊酸盐脂质体中可以恢复与完整膜观察到的类似的配体结合模式。
