Human glutathione transferase P1-1 and nitric oxide carriers; a new role for an old enzyme

• Published in: The Journal of biological chemistry 2001-11, Vol.276 (45), p.42138-42145
• Main Authors: Lo Bello, M, Nuccetelli, M, Caccuri, A M, Stella, L, Parker, M W, Rossjohn, J, McKinstry, W J, Mozzi, A F, Federici, G, Polizio, F, Pedersen, J Z, Ricci, G
• Format: Article
• Language: English
• Subjects: Binding, Competitive; Electron Spin Resonance Spectroscopy; Glutathione - metabolism; Glutathione - pharmacology; Glutathione S-Transferase pi; Glutathione Transferase - physiology; Humans; Iron - metabolism; Isoenzymes - physiology; Mass Spectrometry; Nitric Oxide - metabolism; Nitrogen Oxides - metabolism; Protein Binding; S-Nitrosoglutathione - metabolism; S-Nitrosoglutathione - pharmacology; Serum Albumin - metabolism
• ISSN: 0021-9258
• DOI: 10.1074/jbc.M102344200

S-Nitrosoglutathione and the dinitrosyl-diglutathionyl iron complex are involved in the storage and transport of NO in biological systems. Their interactions with the human glutathione transferase P1-1 may reveal an additional physiological role for this enzyme. In the absence of GSH, S-nitrosoglutathione causes rapid and stable S-nitrosylation of both the Cys(47) and Cys(101) residues. Ion spray ionization-mass spectrometry ruled out the possibility of S-glutathionylation and confirms the occurrence of a poly-S-nitrosylation in GST P1-1. S-Nitrosylation of Cys(47) lowers the affinity 10-fold for GSH, but this negative effect is minimized by a half-site reactivity mechanism that protects one Cys(47)/dimer from nitrosylation. Thus, glutathione transferase P1-1, retaining most of its original activity, may act as a NO carrier protein when GSH depletion occurs in the cell. The dinitrosyl-diglutathionyl iron complex, which is formed by S-nitrosoglutathione decomposition in the presence of physiological concentrations of GSH and traces of ferrous ions, binds with extraordinary affinity to one active site of this dimeric enzyme (K(i) < 10(-12) m) and triggers negative cooperativity in the vacant subunit (K(i) = 10(-9) m). The complex bound to the enzyme is stable for hours, whereas in the free form and at low concentrations, its life time is only a few minutes. ESR and molecular modeling studies provide a reasonable explanation of this strong interaction, suggesting that Tyr(7) and enzyme-bound GSH could be involved in the coordination of the iron atom. All of the observed findings suggest that glutathione transferase P1-1, by means of an intersubunit communication, may act as a NO carrier under different cellular conditions while maintaining its well known detoxificating activity toward dangerous compounds.