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From Proteopedia

Revision as of 11:43, 30 January 2016

Introduction

Endothelial Nitric Oxide Synthase (eNOS)^[1] is a major actor in the regulation of cardiovascular processes, since it induces the production of Nitric Oxide (NO) in vascular endothelial cells. NO is involved in several processes such as vessel vasodilatation, vascular smooth muscle cell proliferation, angiogenesis. The activity of eNOS is related to intracellular calcium concentration and its activation requires the calcium binding protein, CalModulin (CaM).

The structure of CaM protein bound to the CaM binding domain of eNOS has been obtained thanks to a solution NMR^[2], a nuclear magnetic resonance that enables the determination of structures but also interactions between molecules.

Structure and function

Production of NO

Structure of CaM

Calmodulin is a 148-amino-acid peptide containing 2 symmetrical globular calcium domains connected by a flexible central linker region that is a 28-amino-acid-long alpha helix. The are the first calcium domain and the are the second one. CaM has 4 EF hand motifs (2 at each globular calcium binding domain) highly conserved among calcium binding proteins. EF hand motif is suitable for the binding of one calcium ion since an electronegative environment is established.

Structure of eNOS

eNOS is a homodimeric enzyme consisting of two main domains : a N-terminal oxygenase domain and a C-terminal reductase domain. The N-terminal oxygenase domain is composed of the heme and tetrahydrobiopterin (H4B) cofactors and the binding site for the substrates L-arginine and oxygen whereas the FMN binding subdomain and FAD/NADPH binding subdomains are included in the C-terminal reductase. Those two domains are connected by a CaM binding domain which is essential for the efficient transfer of an electron from the reductase domain of one monomer to the heme domain of the adjacent monomer in order to produce NO^[3].

Interaction between CaM and the CaM binding domain peptide of eNOS

In an antiparallel manner, the N-terminal _helices I–IV_ and C-terminal domains _helices VI–VIII_ of CaM mainly interact with hydrophobic residues of eNOS Phe496, Ala500, Val503 and Leu509. The two CaM termini cinch around the α-helical core of eNOS _ Phe496-Ala507_ while basic residues at the eNOS N-terminal Arg492, Lys493, Lys494 bind through electrostatic forces to glutamate residues at CaM termini.

The 3D structure^[4] shown here represents the interaction between the and the .

Disease

As NO has a really important role in cardiovascular processes, a malfunction in the production of NO can contribute to diseases such as atherosclerosis, hypertension.

References

1. ↑ eNOS signaling[1]
2. ↑ Solution NMR, Instruct Interacting Biology[2]
3. ↑ Nitric oxide synthase domain interfaces regulate electron transfer and calmodulin activation, Brian C. Smith, Eric S. Underbakke, Daniel W. Kulp, William R. Schief and Michael A. Marletta[3]
4. ↑ Structure from PDB[4]