Nos1

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Location

The human gene NOS1, found on chromosome 12, encodes for a nitric oxide synthase which is ubiquitously expressed. Nitric oxide synthases consume L-arginine to produce nitric oxide. The chemical equation is shown below.

2 L-arginine + 3 NADPH + 4 O(2) = 2 L- citrulline + 2 nitric oxide + 3 NADP(+) + 4 H(2)O

Nitric oxide is used in a wide variety of processes. A few examples of molecular processes include heme binding, NADP binding, calcium signaling, and oxidation-reduction reactions. Biological examples include regulation of cardiac muscle contraction, blood coagulation, aging, and regulation of neurogenesis ^[3]. There are three known isoforms known for NOS1 in humans produced by alternative splicing, as well as four natural transcript variants for NOS1. The alternatively-spliced isoforms are reffered to as neuronal NOS (nNOS or NOS1), endothelial NOS (eNOS or NOS3), and cytokine-inducible NOS (iNOS or NOS2). Moderate expression of NOS1 has been observed in skeletal muscle, brain, testicular, lung, and kidney tissue. Low expression has been observed in heart, adrenal gland, and retinal tissues ^[4].

Function

Disease

Relevance

Structural highlights

Nos exists as a homodimer. This homodimer consists of two regions. One region is an N-terminal oxygenase domain and the other is a C-terminal reductase. The N-terminal oxygenase domain is an extended beta sheet cage with binding sites for heme and pterin. Nos has a N-terminal catalytic domain with a heme active site. Nos 1 also has a cofactor site nearby for tetrahydrobiopterin (H4B). Nos has a C-terminal reductase domain containing FMN, FAD and NADPH binding sites. Electrons are passed from FAD to FMN and then to the heme. This electron flow is controlled by the binding of CaM and Ca2+ in the linker region between the two major domains. The linker between the oxygenase and reductase domains contains a calmodulin-binding sequence. Nos1 is found in neuronal tissue.

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