Paramagnetic NMR spectroscopy and coordination structure of cobalt(II) Cys112Asp azurin

Paramagnetic ^1H-NMR spectra of Co(II)-substituted Cys112Asp azurin from Pseudomonas aeruginosa have been analyzed and compared with those of the Co(II) wild-type (WT) protein. Hyperfine-shifted signals (including Asp112 β-CH_2 signals in the mutant as well as previously unobserved Cys112 β-CH_2 signals in WT) from all the metal-coordinated residues have been detected and unambiguously assigned. Notably, the spectra indicate that very little if any unpaired spin density is located on the Met121 protons in the Cys112Asp protein. A computer-generated model of the mutant Co(II) structure consistent with electronic absorption as well as the NMR data includes a Gly45 carbonyl, His46, an unusually coordinated Asp112, and His117 in the ligation sphere.