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 ribonucleaseA, determined at 0.87 Å resolution, reveals a highly significantnegative correlation between CN and CO bond distances in peptidegroups. This trend, i.e. the CO bond lengthens when the CN bondshortens, is also found in seven out of eight protein structures,determined at ultrahigh resolution (<0.95 Å). In fiveof them the linear correlation is statistically significantat the 95% confidence level. The present findings are consistentwith the traditional view of amide resonance and, although alreadyfound in small peptide structures, they represent a new andimportant result. In fact, in a protein structure the fine detailsof the peptide geometry are only marginally affected by thecrystal field and they are mostly produced by intramolecularand solvent interactions. The analysis of very high-resolutionprotein structures can reveal subtle information about localelectronic features of proteins which may be critical to folding,function or ligand binding.