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Related Concept Videos

Nitric Oxide Signaling Pathway01:28

Nitric Oxide Signaling Pathway

Nitric oxide (NO), an inorganic gas, acts as a potent second messenger in most animal and plant tissues. NO diffuses out of the cells that produce it and enters the neighboring cells to generate a downstream response. NO synthase (NOS) catalyzes NO production by the deamination of the amino acid arginine. There are three isoforms of NOS. Endothelial cells have endothelial NOS (eNOS), nerve and muscle cells have neuronal NOS (nNOS), and macrophages produce inducible NOS (iNOS) upon exposure to...
Calmodulin-dependent Signaling01:16

Calmodulin-dependent Signaling

Calmodulin (CaM) is a calcium-binding protein in eukaryotes that controls various calcium-regulated cellular processes. It has four calcium-binding sites that bind calcium to form the calcium-calmodulin ( Ca2+-CaM) complex. GPCR stimulation increases the calcium levels in the cells that bind to CaM and induces a conformational change.
The Ca2+-CaM complex does not have enzymatic activity by itself. Instead, the complex binds downstream target proteins, including membrane proteins or enzymes,...
Electron Transport Chain: Complex III and IV01:43

Electron Transport Chain: Complex III and IV

During the electron transport chain, electrons from NADH and FADH2 are first transferred to complexes I and II, respectively. These two complexes then transfer the electrons to ubiquinol, which carries them further to complex III. Complex III passes the electrons across the intermembrane space to Cyt c, which carries them further to complex IV. Complex IV donates electrons to oxygen and reduces it to water. As electrons pass through complexes I, III, and IV, the energy released aids the pumping...
Electron Transport Chain: Complex I and II01:46

Electron Transport Chain: Complex I and II

The mitochondrial electron transport chain (ETC) is the main energy generation system in the eukaryotic cells. However, mitochondria also produce cytotoxic reactive oxygen species (ROS) due to the large electron flow during oxidative phosphorylation. While Complex I is one of the primary sources of superoxide radicals, ROS production by Complex II is uncommon and may only be observed in cancer cells with mutated complexes.
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Assembly of Signaling Complexes01:30

Assembly of Signaling Complexes

Multiprotein signaling complexes are formed in a dynamic process involving protein-protein interactions at the cytoplasmic domain of transmembrane receptors or enzymatic and non-enzymatic proteins associated with the receptor. These complexes ensure the activation and propagation of intracellular signals that regulate cell functions.
Interaction domains in cell signaling
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The Supercomplexes in the Crista Membrane

The mitochondrial cristae membrane is the primary site for the oxidative phosphorylation (OXPHOS) process of energy conversion mediated through respiratory complexes I to V. These complexes have been widely studied for decades, and it has been proven that they form supramolecular structures called respiratory supercomplexes (SC). These higher-order complexes may be crucial in maintaining the biochemical structure and improving the physiological activity of the individual complexes while...

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Related Experiment Video

Updated: May 8, 2026

Application of Genetically Encoded Fluorescent Nitric Oxide (NO•) Probes, the geNOps, for Real-time Imaging of NO• Signals in Single Cells
08:32

Application of Genetically Encoded Fluorescent Nitric Oxide (NO•) Probes, the geNOps, for Real-time Imaging of NO• Signals in Single Cells

Published on: March 16, 2017

Nitric oxide synthase domain interfaces regulate electron transfer and calmodulin activation.

Brian C Smith1, Eric S Underbakke, Daniel W Kulp

  • 1Departments of Chemistry and Immunology and Microbial Science, The Scripps Research Institute, La Jolla, CA 92037.

Proceedings of the National Academy of Sciences of the United States of America
|September 5, 2013
PubMed
Summary

This study reveals how nitric oxide synthase (NOS) domains interact with calmodulin to facilitate electron transfer, essential for nitric oxide (NO) production in physiological processes.

Keywords:
NO signalingflavinhemoproteiniNOS

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Area of Science:

  • Biochemistry
  • Molecular Biology
  • Enzymology

Background:

  • Nitric oxide synthase (NOS) produces nitric oxide (NO), vital for vasodilation, neurotransmission, and immune responses.
  • NOS enzymes are homodimers with distinct oxidase and reductase domains, but their overall structure and activation mechanisms remain unclear.
  • Understanding NOS structure is crucial for elucidating NO synthesis and calmodulin's regulatory role.

Purpose of the Study:

  • To determine the higher-order domain architecture of NOS holoenzymes.
  • To elucidate the electron transfer pathway from FMN to heme within NOS.
  • To investigate the mechanism of calmodulin-mediated activation of NOS.

Main Methods:

  • Hydrogen-deuterium exchange mass spectrometry (HDX-MS) to map NOS interaction surfaces.
  • Kinetic studies of site-specific interface mutants.
  • Computational docking to model NOS domain-calmodulin interactions.

Main Results:

  • HDX-MS identified direct interactions between NOS heme and FMN subdomains and calmodulin.
  • Kinetic studies validated the identified interaction surfaces.
  • Integrated HDX-MS and docking yielded models of NOS-calmodulin complexes.

Conclusions:

  • The study proposes a pathway for electron transfer from FMN to heme in NOS.
  • A mechanism for calmodulin's activation of this critical electron transfer step is suggested.
  • These findings advance the understanding of NO production regulation at a molecular level.