Ab initio NMR chemical shift calculations on proteins using fragment molecular orbitals with electrostatic environment

An efficient computational method to calculate NMR chemical shifts of large biomolecular systems is proposed. The method is based on the fragment molecular orbital (FMO) method combined with the gauge-including atomic orbital (GIAO) and continuous set of gauge transformations (CSGT) methods. It accurately reproduced the conventional ab initio NMR values for a 10-residues peptide. The method was also applied to ubiquitin (76 amino-acid residues), and the calculated chemical shifts agree well with experimentally measured shifts. The proposed method requires a much lower computational cost than the conventional ab initio methods to calculate chemical shifts of large systems.

Correlations between calculated absolute isotropic shielding constants of model 10-residue polypeptide (inset) obtained from FMO-based and conventional CSGT methods (6-31G(d)).