Human Glutathione Transferase P1-1 and Nitric Oxide Carriers. A new role for an old enzyme

Mario Lo Bello, Marzia Nuccetelli, Anna M. Caccuri, Lorenzo Stella, Michael W. Parker, Jamie Rossjohn, William J. McKinstry, Alessia F. Mozzi, Giorgio Federici, Francesca Polizio, Jens Z. Pedersen, Giorgio Ricci

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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 Cys47 and Cys101 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-Ni-trosylation 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 (Ki < 10-12 M) and triggers negative cooperativity in the vacant subunit (Ki = 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.

Original languageEnglish
Pages (from-to)42138-42145
Number of pages8
JournalJournal of Biological Chemistry
Issue number45
Publication statusPublished - 9 Nov 2001
Externally publishedYes

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