Human glutathione transferase P1-1 and nitric oxide carriers; a new role for an old enzyme.
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.
Lo Bello
M
M
Department of Biology, University of Rome "Tor Vergata," 00133 Rome, Italy.
Nuccetelli
M
M
Caccuri
A M
AM
Stella
L
L
Parker
M W
MW
Rossjohn
J
J
McKinstry
W J
WJ
Mozzi
A F
AF
Federici
G
G
Polizio
F
F
Pedersen
J Z
JZ
Ricci
G
G
D001667:Binding, Competitive; D004578:Electron Spin Resonance Spectroscopy; D005978:Glutathione / Q000378:metabolism / Q000494:pharmacology; D051549:Glutathione S-Transferase pi; D005982:Glutathione Transferase / Q000502:physiology*; D006801:Humans; D007501:Iron / Q000378:metabolism; D007527:Isoenzymes / Q000502:physiology*; D013058:Mass Spectrometry; D009569:Nitric Oxide / Q000378:metabolism*; D009589:Nitrogen Oxides / Q000378:metabolism; D011485:Protein Binding; D026422:S-Nitrosoglutathione / Q000378:metabolism / Q000494:pharmacology; D012709:Serum Albumin / Q000378:metabolism
D007527:Isoenzymes; D009589:Nitrogen Oxides; D012709:Serum Albumin; D009569:Nitric Oxide; D026422:S-Nitrosoglutathione; C073661:dinitrosyl iron complex; D007501:Iron; C496556:GSTP1 protein, human; D051549:Glutathione S-Transferase pi; D005982:Glutathione Transferase; D005978:Glutathione