Electron density in the peptide bonds of crambin

The electron density in the peptide bonds of crambin, a plant-seed hydrophobic globular protein with 46 residues and 642 atoms, is studied both theoretically and experimentally. The results of density functional calculations of crambin in vacuo for the deformation electron density in its peptide bonds are compared with the electronic distribution obtained from ultra-high-resolution X-ray crystallography. The comparison is centered on the average peptide-bond map, where the experimental results are clearest. Theory is then used to ascertain on differences among peptide bonds in different chemical environments.