Nitric oxide synthase (NOS), a flavo-hemoprotein, tightly regulates nitric oxide (NO) synthesis and thereby its dual biological activities as a key signaling molecule for vasodilatation and neurotransmission at low concentrations, and also as a defensive cytotoxin at higher concentrations. Three NOS isoforms, iNOS, eNOS and nNOS (inducible, endothelial, and neuronal NOS), achieve their key biological functions by tight regulation of interdomain electron transfer (IET) process via interdomain interactions. Our long-term goal is to determine the molecular mechanism of NOS enzyme catalysis, including how the interdomain interactions modulate the catalytically relevant IET processes and the NOS enzyme function. In this project we will focus on investigating important roles of the FMN domain docking to the heme domain in regulating the NOS isoform function. An exciting recent development in the NOS enzymes is the discovery of importance of the interdomain FMN-heme interactions for modulating reactivity and structure of the catalytic heme active site. The recent findings raise two new important mechanistic questions that must be addressed to understand NOS regulation mechanism: 1) what specific interdomain interactions govern and facilitate the productive docking of the FMN domain to the heme domain? 2) how can the FMN domain docking, in addition to controlling the catalytically essential FMN-heme IET, modulate reactivity of the heme active site? Our two synergistic and complementary Aims are designed to directly address these important questions. We will employ an integrated program of pulsed electron paramagnetic resonance, laser flash photolysis and mutational studies. In the absence of a structure of full-length mammalian NOS, the combined approach is highly appropriate for the proposed study. This project seeks to address fundamental questions relating to the NOS enzymes. Our study will identify key structural determinants in controlling NOS isoform activity by modulating the alignment of the FMN and heme domains. The new information could facilitate bio-rational development of new selective activators or inhibitors for these clinically important enzymes, in order to provide better therapeutic interventions. In accordance with the guideline of the R15 program we will continue to train our 21st century biomedical scientists by this multi-disciplinary project.

Public Health Relevance

The NOS family is a key target for development of new pharmaceuticals for a wide range of diseases that currently lack effective treatments, including stroke and cancer. However, due to an incomplete understanding of the molecular mechanisms of NOS regulation, NOS inhibitors have not yet been available for clinical treatments. The proposed studies will significantly improve the fundamental understanding of NOS isoform regulation, and could facilitate bio-rational development of new selective mechanism-based drug entities to target these clinically important enzymes.

National Institute of Health (NIH)
National Institute of General Medical Sciences (NIGMS)
Academic Research Enhancement Awards (AREA) (R15)
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Macromolecular Structure and Function A Study Section (MSFA)
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Anderson, Vernon
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University of New Mexico Health Sciences Center
Schools of Pharmacy
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Astashkin, Andrei V; Li, Jinghui; Zheng, Huayu et al. (2018) A docked state conformational dynamics model to explain the ionic strength dependence of FMN - heme electron transfer in nitric oxide synthase. J Inorg Biochem 184:146-155
Zheng, Huayu; He, Jingxuan; Li, Jinghui et al. (2018) Generation and characterization of functional phosphoserine-incorporated neuronal nitric oxide synthase holoenzyme. J Biol Inorg Chem :
Li, Jinghui; Zheng, Huayu; Wang, Wei et al. (2018) Role of an isoform-specific residue at the calmodulin-heme (NO synthase) interface in the FMN - heme electron transfer. FEBS Lett 592:2425-2431
Chen, Li; Zheng, Huayu; Li, Wenbing et al. (2016) Role of a Conserved Tyrosine Residue in the FMN-Heme Interdomain Electron Transfer in Inducible Nitric Oxide Synthase. J Phys Chem A 120:7610-7616
McQuarters, Ashley B; Speelman, Amy L; Chen, Li et al. (2016) Exploring second coordination sphere effects in nitric oxide synthase. J Biol Inorg Chem 21:997-1008
Sheng, Yinghong; Zhong, Linghao; Guo, Dahai et al. (2015) Insight into structural rearrangements and interdomain interactions related to electron transfer between flavin mononucleotide and heme in nitric oxide synthase: A molecular dynamics study. J Inorg Biochem 153:186-196
Astashkin, Andrei V; Feng, Changjian (2015) Solving Kinetic Equations for the Laser Flash Photolysis Experiment on Nitric Oxide Synthases: Effect of Conformational Dynamics on the Interdomain Electron Transfer. J Phys Chem A 119:11066-75
Astashkin, Andrei V; Chen, Li; Elmore, Bradley O et al. (2015) Probing the Hydrogen Bonding of the Ferrous-NO Heme Center of nNOS by Pulsed Electron Paramagnetic Resonance. J Phys Chem A 119:6641-9
Feng, Changjian; Chen, Li; Li, Wenbing et al. (2014) Dissecting regulation mechanism of the FMN to heme interdomain electron transfer in nitric oxide synthases. J Inorg Biochem 130:130-40
Astashkin, Andrei V; Chen, Li; Zhou, Xixi et al. (2014) Pulsed electron paramagnetic resonance study of domain docking in neuronal nitric oxide synthase: the calmodulin and output state perspective. J Phys Chem A 118:6864-72

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