S-Nitrosylation signaling regulates cellular protein interactions

Abstract

Background: S-Nitrosothiols are made by nitric oxide synthases and other metalloproteins. Unlike nitric oxide, S-nitrosothiols are involved in localized, covalent signaling reactions in specific cellular compartments. These reactions are enzymatically regulated.

Scope: S-Nitrosylation affects interactions involved in virtually every aspect of normal cell biology. This article is part of a Special Issue entitled Regulation of Cellular Processes by S-nitrosylation.

Major conclusions and significance: S-Nitrosylation is a regulated signaling reaction.

Copyright © 2011 Elsevier B.V. All rights reserved.

Figures

Figure 1. Scientific overview: An emerging paradigm of nitrogen oxide signaling

Nitric oxide synthase (NOS) forms S-nitrosothiols (RS˙-˙NO, or, more commonly, RS−−NO+). Note there is also regulated cellular import of extracellular S-nitrosothiols. NOS-derived NO and NO reduced from S-nitrosothiols and NO2− can exert classical cytotoxic and cyclic GMP (cGMP)-dependent effects, the latter through activation of guanylyl cyclase (GC). Intracellular S-nitrosothiols can include protein and low-mass species, and are generally in sequestered locations in the cell, such as membranes and vesicles. These S-nitrosothiols can transfer NO+ equivalents to target proteins through transnitrosylation to cause cGMP-independent effects; this signaling can be regulated by movement of the S-nitrosothiols in the cell to target locations, and by degradation. Dr. Lewis’ recent data suggest that S-nitrosothiols can also be secreted into the extracellular space to signal intercellular, cGMP-independent effects—particularly in the autonomic nervous system—through extrusion from S-nitrosothiol-containing vesicles.

Figure 2. Effect of S-nitrosylation on the 3D structure of human ApoE3

(A) Fully processed ApoE3, without the N-terminal signal peptide sequence (18 residues), is comprised of an N-terminal LDL receptor binding (RB) domain and a C-terminal lipid binding (LB) domain. Note that all the amino acid numbering used here is based on the amino acid sequence of the fully processed ApoE (residues 1−299). (B) 3D atomic model of the WT RB domain of ApoE. (C) 3D atomic model of the S-nitrosothiol derivative (C112SNO) of the RB domain of ApoE. Note that in both panels B and C, the RB domains are colored brown while the side chain moieties of R61, E109, and C112/C112SNO are colored blue, red, and green, respectively. Insets show close-ups of intramolecular interactions of C112/C112SNO with R61 and E109. (D) Schematic showing the S-nitrosylation of C112 within the RB domain of ApoE. Note that the resulting C112SNO S-nitrosothiol derivative may undergo resonance arrangement to form a zwitterion with an internal dipole characterized by the separation of a positive charge and a negative charge on sulfur and oxygen atoms, respectively. (E) Schematic showing a plausible hydrogen bonding and/or ion pairing network of the polarized S-nitrosothiol moiety of C112SNO, the guanidino group of R61, and the side chain carboxylate of E109. The double-headed red arrows indicate potential hydrogen bonding and/or ion pairing contacts. (from reference 14)

Figure 3. eNOS as a Nitrosonium Synthase

A. Proteins were immunoprecipitated with anti-CSNO antibody before, and two and 10 min after, cell treatment with calcium ionophore A23187; they were then immunoblotted with anti-eNOS. B. Proposed general schematic of nitrosonium (NO+) transfer following eNOS activation, based on our preliminary data. Arrows represent transnitrosylation (NO+ transfer between cysteines). Protein-scaffolding scheme adapted from Su, Kondrikov, and Block (ref. 25).