IBR   13079
INSTITUTO DE BIOLOGIA MOLECULAR Y CELULAR DE ROSARIO
Unidad Ejecutora - UE
artículos
Título:
Electron Spin Density on the Axial His Ligand of High-Spin and Low-Spin Nitrophorin 2 Probed by Heteronuclear NMR Spectroscopy
Autor/es:
ABRIATA LA; M.E. ZABALLA; R.E. BERRY; F. YANG; H. ZHANG; F.A.WALKER; AJ. VILA
Revista:
INORGANIC CHEMISTRY
Editorial:
AMER CHEMICAL SOC
Referencias:
Lugar: Washington; Año: 2013 vol. 52 p. 1285 - 1295
ISSN:
0020-1669
Resumen:
The electronic structure of
heme proteins is exquisitely tuned by the interaction of the iron center with
the axial ligands. NMR studies of paramagnetic heme systems have been focused
on the heme signals, but signals from the axial ligands have been rather difficult to detect and assign. We report an extensive assignment of the 1 H,13 C and 15 N resonances of the axial His ligand in the NO-carrying protein nitrophorin
2 (NP2) in the paramagnetic high-spin and low- spin forms, as well as in the
diamagnetic NO complex. We find that the
high-spin protein has σ spin delocalization to all atoms in the axial His57, which decreases in
size as the number of bonds between Fe(III) and the
atom in question increases, except that within the His57 imidazole ring the
contact shifts are a balance between positive σ and negative π contributions.
In contrast, the low-spin protein has π spin delocalization to all atoms
of the imidazole ring. Our strategy, adequately combined with a selective
residue labeling scheme, represents a straightforward
characterization of the electron spin density in heme axial ligands.