Popova N A, Soodaeva S K, Klimanov I A, Misharin V M, Temnov A A
Researcher, Laboratory of Clinical and Experimental Biophysics; Pulmonology Research Institute, Federal Medical and Biological Agency of Russia, 28 Orekhovy Boulevard, Moscow, 115682, Russia; Researcher, Laboratory of Chemical and Biotechnological Synthesis; Moscow Institute of Physics and Technology (National Research University), 9 Institutskiy Per., Dolgoprudny, Moscow Region, 141701, Russia.
Head of Laboratory of Clinical and Experimental Biophysics; Pulmonology Research Institute, Federal Medical and Biological Agency of Russia, 28 Orekhovy Boulevard, Moscow, 115682, Russia; Leading Researcher, Laboratory of Chemical and Biotechnological Synthesis; Moscow Institute of Physics and Technology (National Research University), 9 Institutskiy Per., Dolgoprudny, Moscow Region, 141701, Russia.
Sovrem Tekhnologii Med. 2023;15(3):53-59. doi: 10.17691/stm2023.15.3.06. Epub 2023 May 28.
Nitric oxide (II) (NO) is the most important mediator of a wide range of physiological and pathophysiological processes. It is synthesized by NO synthases (NOSs), which have three main isoforms differing from each other in terms of activation and inhibition features, levels of NO production, subcellular localization, etc. At the same time, all isoforms are structurally very similar, and these differences are determined by NOS autoregulatory elements. The article presents an analysis of the autoregulatory and autoinhibitory mechanisms of the NOS reductase domain that determine differences in the productivity of isoforms, as well as their dependence on the concentration of Ca ions. The main regulatory elements in NOS that modulate the electron transfer from flavin to heme include calmodulin (CaM), an autoinhibitory insert (AI), and the C-terminal tail (C-tail). Hydrophobic interactions of CaM with the surface of the NOS oxidase domain are assumed to facilitate electron transfer from flavin mononucleotide (FMN). CaM binding causes a change in the inter-domain distances, a shift of AI and the C-tail, and, as a result, a decrease in their inhibitory effect. CaM also shifts the conformational equilibrium of the reductase domain towards more open conformations, reduces the lifetime of conformations, their stereometric distribution, and accelerates the flow of electrons through the reductase domain. The AI element, apparently, induces a conformational change that hinders electron transfer within the reductase domain, similar to the hinge domain in cytochrome P450. Together with CaM, the C-tail regulates the electron flow between flavins, the distance and relative orientation of isoalloxane rings, and also modulates the electron flow from FMN to the terminal acceptor. Together with the C-tail, AI also predetermines the dependence of neuronal and endothelial forms of NOS on the concentration of Ca ions, and the C-tail length affects differences in the productivity of NO synthesis. The inhibitory effect of the C-tail is likely to be reduced by CaM binding due to the C-tail shift due to the electrostatic repulsive forces of the negatively charged phosphate and aspartate residues. The autoregulatory elements of NOS require further study, since the mechanisms of their interaction are complex and multidirectional, and hence provide a wide range of characteristics of the observed isoforms.
一氧化氮（II）（NO）是多种生理和病理生理过程中最重要的介质。它由一氧化氮合酶（NOSs）合成，NOSs有三种主要亚型，在激活和抑制特性、NO产生水平、亚细胞定位等方面彼此不同。同时，所有亚型在结构上非常相似，这些差异由NOS自身调节元件决定。本文对NOS还原酶结构域的自身调节和自身抑制机制进行了分析，这些机制决定了亚型活性的差异以及它们对钙离子浓度的依赖性。NOS中调节从黄素到血红素电子传递的主要调节元件包括钙调蛋白（CaM）、一个自身抑制插入序列（AI）和C末端尾巴（C-tail）。推测CaM与NOS氧化酶结构域表面的疏水相互作用有助于从黄素单核苷酸（FMN）进行电子传递。CaM结合会导致结构域间距离改变、AI和C-tail移位，结果是它们的抑制作用减弱。CaM还会使还原酶结构域的构象平衡向更开放的构象转变，减少构象的寿命、它们的立体测量分布，并加速电子通过还原酶结构域的流动。AI元件显然会诱导一种构象变化，阻碍还原酶结构域内的电子传递，类似于细胞色素P450中的铰链结构域。与CaM一起，C-tail调节黄素之间的电子流动、异咯嗪环的距离和相对取向，还调节从FMN到末端受体的电子流动。与C-tail一起，AI还预先决定了神经元型和内皮型NOS对钙离子浓度的依赖性，并且C-tail的长度影响NO合成活性的差异。由于带负电荷的磷酸和天冬氨酸残基的静电排斥力导致C-tail移位，CaM结合可能会降低C-tail的抑制作用。NOS的自身调节元件需要进一步研究，因为它们的相互作用机制复杂且具有多向性，因此提供了所观察到的亚型的广泛特征。
