Arg199: key player in electron transfer in NOS enzyme

描述（由申请人提供）：一氧化氮合成酶（NOS）家族催化l -精氨酸转化为l -瓜氨酸和一氧化氮（NO），一氧化氮是一种重要的细胞信使分子，涉及多种病理生理状况，如感染性休克、炎症功能障碍、神经退行性疾病状态，最重要的是心血管疾病。然而，尽管人们对一氧化氮在各种疾病中的作用的了解有所增加，但有效的治疗方法仍有待于对一氧化氮的结构-功能关系的完全理解。这种理解对于通过设计更有效的调节药物来调节体内内源性一氧化氮的产生是必不可少的。NOS活性位点具有独特的协同结构-功能和电子特性（动态和协同协同工作），专门为NOS酶的功能进行了调整。这个系统的复杂性需要使用复杂的计算方法，以便充分理解和表征这种酶的功能机制。然而，迄今为止，尚未利用第一性原理量子力学（QM）和复合量子力学和分子力学（QM/MM）方法，结合分子动力学（MD）模拟和各种其他计算分析工具进行全面的计算研究。因此，这项建议的意图有三个方面：(1)通过MD模拟研究NOS环境，以充分表征四氢生物terin （H4B）辅因子（精氨酸氧化的及时电子源）的动力学行为，其自由基种类已在电子自旋共振实验中被发现；(2)通过QM和QM/MM计算及电子转移途径建模，分析促进该自由基种类形成的酶环境；为了确定空腔内促进电子从辅助因子转移到血红素-二氧基中间体的关键分子，(3)通过计算调查和阐明这些关键分子在NOS电子转移中的作用，试图指导未来的实验和药理干预，以抑制这一重要酶。主要的焦点放在Arg199如何调节NOS中的电子转移，这一作用仅在系统动力学中揭示。

DESCRIPTION (provided by applicant): The family of nitric oxide synthases (NOS) catalyzes the conversion of L-arginine to L-citrulline and nitric oxide (NO), an important cellular messenger molecule, which has been implicated in a variety of pathophysiological conditions such as septic shock, inflammatory dysfunction, neurodegenerative disease states, and, most importantly, cardiovascular disease. However, despite the increased understanding of the role of NO in contributing to various conditions, effective therapies still await the complete understanding of structure-function relationships within NOS. This understanding is imperative for the modulation of endogenous NO production in vivo, through the design of more effective regulatory drugs. It is proposed that the NOS active site possesses unique synergetic structural-function and electronic properties (which work together both dynamically and cooperatively) specifically tuned for the NOS enzyme functionality. The complexities of this system require the use of sophisticated computational methodologies, in order to fully understand and characterize the functioning mechanism of this enzyme. However, to date, a full-length comprehensive computational investigation, using first principle quantum mechanical (QM) and composite quantum mechanical and molecular mechanics (QM/MM) methodologies, coupled with molecular dynamics (MD) simulation and a variety of other computational analysis tools, has yet to be utilized. Therefore, the intent of this proposal is three fold: (1) to study the NOS environment through MD simulations, in order to fully characterize the dynamic behavior of the tetrahydrobiopterin (H4B) cofactor (a timely electron source for arginine oxidation), whose radical species has been previously identified in electron spin resonance experiments, (2) to analyze the enzyme environment that facilitates the formation of this radical species through QM and QM/MM calculations and electron transfer pathway modeling, in order to identify the key molecular players within the cavity which promote the electron transfer from the cofactor to the heme ferrous-dioxy intermediate, (3) to investigate and elucidate, through computation, the roles of these key players in the electron transfer within NOS, in attempts to direct future experimental and pharmacological interventions into the inhibition of this important enzyme. Primary focus is placed on how Arg199 modulates the electron transfer in NOS a role only revealed during the dynamics of the system.