Structure of the metal site in Rhus vernicifera stellacyanin: A paramagnetic NMR study on its Co(II) derivative

The H-1 NMR spectrum of Co(II)-substituted stellacyanin from Rhus vernificera has been recorded and the hyperfine-shifted signals corresponding to metal ligands have been assigned by means of 1D and 2D NOE spectra. Two His and a Cys coordinate the metal ion, and a Gin residue is the axial metal ligand. The beta-CH2 Cys proton shifts reflect a decreased electron delocalization onto this residue when compared to azurin. Both His residues are solvent accessible. This fact could contribute to the low redox potential of this protein. This work provides the first experimental evidence of a Gin coordination to the metal in a native blue copper protein.