Protein structure refinement using carbon-13 nuclear magnetic resonance spectroscopic chemical shifts and quantum chemistry

The calculated backbone torsion angles phi, psi and chi for the 12 alanine and 8 valine residues in the nuclease from Staphylococcus aureus using radioactive carbon chemical shifts, are identical to that of the X-ray determined values when nuclear Overhauser effect distance restraints and J-coupling torsion angle restraints are combined with chemical shift restraints. The fully-restrained set of structures analyzed with and without chemical shift constraints have some nuclear Overhauser effect violations.