Self-consistent 3J coupling analysis for the joint calibration of Karplus coefficients and evaluation of torsion angles

The concept of self-consistent J coupling evaluation exploits redundant structure information inherent in large sets of (3)J coupling constants. Application to the protein Desulfovibrio vulgaris flavodoxin demonstrates the simultaneous refinement of torsion-angle values and related Karplus coefficients. The experimental basis includes quantitative coupling constants related to the polypeptide backbone phi torsion originating from a variety of heteronuclear 2D and 3D NMR correlation experiments, totalling 124 (3)J(H-N,H-alpha), 129 (3)J(H-N,C'), 121 (3)J(H-N,C-beta), 128 (3)J(Ci-1',H-i(alpha)), 121 (3)J(Ci-1',C-i'), and 122 (3)J(Ci-1',C-i(beta)). Without prior knowledge from either X-ray crystallography or NMR data, such as NOE distance constraints, accurate phi dihedral angles are specified for 122 non-glycine and non-proline residues out of a total of 147 amino acids. Different models of molecular internal mobility are considered. The Karplus coefficients obtained are applicable to the conformational analysis of phi torsions in other polypeptides.