Correlation between (super 3h)J(sub NC') and hydrogen bond length in proteins

The establishment of a quantitative connection between backbone-backbone hydrogen-bond (H-bond) length seen in protein crystal structure and (super 3h)J(sub NC') couplings across such bonds is limited by the coordinate precision of the X-ray structure. Very high-resolution X-structures are available for an immunoglobulin binding domain of streptococcal protein G. Findings showed that over the small range of N-O H-bond lengths for which (super 3h)J(sub NC') couplings are observable, the 32 measured (super 3h)J(sub NC') values can be fit to: (super 3h)J(sub NC') = -59000 exp(-4R(sub NO)) +/- 0.09 Hz, or R(sub NO) = 2.75 - 0.25 ln(-(super 3h)J(sub NC')) +/- 0.06 angstrom.