Investigation of Nitric Oxide Synthase Structure, Function and Inhibition

一氧化氮（NO）是一种重要的内源性信使，参与多种生理和病理生理过程。NO是由一氧化氮合酶（NOS）的三种亚型合成的，它们由不同的基因编码，即神经元型（nNOS）、内皮型（eNOS）和诱导型（iNOS）。NO在体内作为第二信使或细胞毒性剂的双重作用显示了对不同NOS亚型的严格调节的重要性。NOS的每个亚基由含有NADPH结合位点的还原酶结构域和两个黄素以及含有血红素、L-精氨酸和四氢生物蝶呤结合位点的加氧酶结构域组成。这两个结构域通过钙调蛋白（CaM）结合结构域连接，该结构域在酶的活化中起重要作用。CaM是钙离子的主要蛋白质介体，也是重要的第二信使。钙调素经历钙依赖的构象变化，使其能够结合和激活包括所有三种NOS同工酶的靶蛋白的分数。本研究计划的两个长期目标是：1）了解CaM结合和控制所有三种NOS同工酶的机制; 2）研究人NOS同工酶的选择性配体结合和抑制。

Nitric oxide (NO) is an important endogenous messenger in a variety of physiological and pathophysiological processes. NO is synthesized by the three isoforms of nitric oxide synthase (NOS) that are encoded by different genes, neuronal (nNOS), endothelial (eNOS) and inducible (iNOS). The dual role of NO in the body as a second messenger or cytotoxic agent shows the importance for tight regulation of the different NOS isoforms. Each subunit of NOS is composed of a reductase domain that contains the binding sites for NADPH, and two flavins as well as an oxygenase domain that contains the binding sites for heme, L-arginine and tetrahydrobiopterin. The two domains are linked by a calmodulin (CaM) binding domain that plays an important role in the activation of the enzyme. CaM is the primary protein mediator of the calcium cation that is also an important secondary messenger. CaM undergoes calcium-dependent conformational changes that allow it to bind and activate scores of target proteins including all three NOS isozymes. Two of the long-term goals of this research program are to: 1) understand the mechanism(s) of CaM binding and control for all three NOS isozymes; 2) study the selective ligand binding and inhibition of human NOS isozymes.