Feng Changjian, Tollin Gordon
College of Pharmacy, University of New Mexico, Albuquerque, NM 87131, USA.
Dalton Trans. 2009 Sep 14(34):6692-700. doi: 10.1039/b902884f. Epub 2009 Jun 17.
There is still much that is unknown about how nitric oxide (NO) biosynthesis by NO synthase (NOS) isoform is tightly regulated at the molecular level. This is remarkable because deviated NO production in vivo has been implicated in an increasing number of diseases that currently lack effective treatments, including stroke and cancer. Given the significant public health burden of these diseases, the NOS enzyme family is a key target for development of new pharmaceuticals. Three NOS isoforms, inducible, endothelial and neuronal NOS (iNOS, eNOS and nNOS, respectively), achieve their key biological functions via stringent regulations of interdomain electron transfer (IET) processes. Unlike iNOS, eNOS and nNOS isoforms are controlled by calmodulin (CaM) binding through facilitating catalytically significant IET processes. The CaM-modulated NOS output state is an IET-competent complex between the flavin mononucleotide (FMN) domain and the catalytic heme domain. The output state facilitates the catalytically essential FMN-heme IET, and thereby enables NO production by NOS. Due to lack of reliable techniques for specifically determining the inter-domain FMN-heme interactions and their direct effects on the catalytic heme center, the molecular mechanism that underlies the output state formation remains elusive. The recent developments in our understanding of mechanisms of the NOS output state formation that are driven by a combination of molecular biology, laser flash photolysis, and spectroscopic techniques are the subject of this perspective.
关于一氧化氮合酶（NOS）同工型如何在分子水平上严格调控一氧化氮（NO）的生物合成，仍有许多未知之处。这一点很值得注意，因为体内一氧化氮生成异常与越来越多目前缺乏有效治疗方法的疾病有关，包括中风和癌症。鉴于这些疾病给公众健康带来的重大负担，NOS酶家族是新型药物开发的关键靶点。三种NOS同工型，即诱导型、内皮型和神经元型NOS（分别为iNOS、eNOS和nNOS），通过严格调控结构域间电子转移（IET）过程来实现其关键生物学功能。与iNOS不同，eNOS和nNOS同工型通过促进具有催化意义的IET过程受钙调蛋白（CaM）结合的控制。CaM调节的NOS输出状态是黄素单核苷酸（FMN）结构域与催化血红素结构域之间的一种具备IET能力的复合物。该输出状态促进了催化必需的FMN - 血红素IET，从而使NOS能够产生NO。由于缺乏用于特异性确定结构域间FMN - 血红素相互作用及其对催化血红素中心直接影响的可靠技术，输出状态形成的分子机制仍然难以捉摸。本文将探讨最近在分子生物学、激光闪光光解和光谱技术相结合的推动下，我们对NOS输出状态形成机制的理解进展。
