Electronic Structure of the Ground and Excited States of the CuA Site by NMR Spectroscopy

L.A.ABRIATA, G.N.LEDESMA, R.PIERATTELLI AND A.J.VILA

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY

American Chemical Society

Lugar: Washington, USA; Año: 2008

0002-7863

The electronic properties of Thermus thermophilus CuA in the oxidized form were studiedby 1H and 13C NMR spectroscopy. All the 1H and 13C resonances from cysteine andimidazole ligands were observed and assigned in a sequence-specific fashion. The detectionof net electron spin density on a peptide moiety is attributed to the presence of a H-bond toa coordinating sulfur atom. This hydrogen-bond is conserved in all natural CuA variants,and is important to maintain the electronic structure of the metal site, rendering the two Cysligands nonequivalent. The anomalous temperature dependence of the chemical shifts isexplained by the presence of a low-lying excited state located about 600 cm-1 above theground state. The room temperature shifts can be described as the thermal average of a σu*ground state and a πu excited state. These results provide a detailed description of theelectronic structure of the CuA site at atomic resolution in solution at physiologicallyrelevant temperature.