The blue copper proteins (BCPs), pseudoazurin from
Achromobacter cycloclastes and rusticyaninfrom
Thiobacillus ferrooxidans, have been investigated by
1H NMR at a magnetic field of 18.8 T. Hyperfineshifts of the protons belonging to the coordinated lig
ands have been identified by exchange spectroscopy,including the indirect detection for those resonances that cannot be directly observed (the
![](/images/gifchars/beta2.gif)
-CH
2 of theCys lig
and,
and the NH amide hydrogen bonded to the S
![](/images/gifchars/gamma.gif)
(Cys) atom). These data reveal that the Cu(II)-Cys interaction in pseudoazurin
and rusticyanin is weakened compared to that in classic blue sites(plastocyanin
and azurin). This weakening is not induced by a stronger interaction with the axial lig
and, asfound in stellacyanin, but might be determined by the protein folding around the metal site. The averagechemical shift of the
![](/images/gifchars/beta2.gif)
-CH
2 Cys lig
and in all BCPs can be correlated to geometric factors of the metal site(the Cu-S
![](/images/gifchars/gamma.gif)
(Cys) distance
and the angle between the CuN
HisN
His plane
and the Cu-S
![](/images/gifchars/gamma.gif)
(Cys) vector). It isconcluded that the degree of tetragonal distortion is not necessarily related to the strength of the Cu(II)-S
![](/images/gifchars/gamma.gif)
(Cys) bond. The copper-His interaction is similar in all BCPs, even for the solvent-exposed His lig
and.It is proposed that the copper
xy magnetic axes in blue sites are determined by subtle geometricaldifferences, particularly the orientation of the His lig
ands. Finally, the observed chemical shifts for
![](/images/gifchars/beta2.gif)
-CH
2Cys
and Ser NH protons in rusticyanin suggest that a less negative charge at the sulfur atom could contributeto the high redox potential (680 mV) of this protein.