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。一氧化氮(NO)由神经型(NNOS)、内皮型(ENOS)和诱导型(INOS)三种不同基因编码的一氧化氮合酶(NOS)合成。NO在体内作为第二信使或细胞毒剂的双重作用表明了严格调控不同的NOS亚型的重要性。一氧化氮合酶的每个亚基由一个含有NADPH结合位点的还原酶域和两个黄素，以及一个含有血红素、L精氨酸和四氢生物蝶呤结合位点的加氧酶结构域组成。这两个结构域由钙调素(CaM)结合结构域连接，该结构域在酶的激活中发挥重要作用。钙调素是钙离子的主要蛋白质介体，也是重要的次要信使。CaM经历钙依赖的构象变化，使其能够结合和激活大量的靶蛋白，包括所有三种一氧化氮合酶同工酶。该研究计划的两个长期目标是：1)了解CaM与三种一氧化氮合酶同工酶的结合和调控机制(S)；2)研究人一氧化氮合酶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.