Experimental evidence for the correlation of bond distances in peptide groups detected in ultrahigh-resolution protein structures

The structural analysis of a deamidated derivative of ribonuclease A, deter mined at 0.87 Angstrom resolution, reveals a highly significant negative co rrelation between CN and CO bond distances in peptide groups. This trend, i .e. the CO bond lengthens when the CN bond shortens, is also found in seven out of eight protein structures, determined at ultrahigh resolution (<0.95 <Angstrom>), In five of them the linear correlation is statistically signi ficant at the 95% confidence level. The present findings are consistent wit h the traditional view of amide resonance and, although already found in sm all peptide structures, they represent a new and important result, In fact, in a protein structure the fine details of the peptide geometry are only m arginally affected by the crystal field and they are mostly produced by int ramolecular and solvent interactions, The analysis of very high-resolution protein structures can reveal subtle information about local electronic fea tures of proteins which may be critical to folding, function or ligand bind ing.