NMR Chemical Shift Map

Most recently, the concept of an NMR chemical shift map has been used to characterize the conformation of synthetic polypeptides and the conformation of any specified amino acid residues of proteins. Here, we are concerned with the chemical shift map as established by a theoretical approach and experimental approach. The amino acid residues except for the proline amino acid residue have the freedom of internal rotation about the two consecutive bonds, NH-C_αHR and C_αHR-CO bonds, where R is the side chain. These torsional angles are defined by Φ and Ψ, respectively. It is very convenient to represent the chemical shift of the amino acid residue as a function of the torsional angles (Φ, Ψ), because the conformation-dependent chemical shift can be obtained and then the conformation can be determined through the chemical shift value. This is the so-called “chemical shift contour map” or “chemical shift map.” This has similar significance to the Ramachandran map for the conformational energy of amino acid residues.