Searching conformational analysis of Asp residues through theoretical (3)J vicinal coupling constants and Karplus equations

The dependence of the vicinal spin-spin coupling constants on the torsion side chain angle chi(1) through the Karplus equations is considered for the study of the structure of Asp amino acid residues. Experimental and theoretical, obtained with density functional theory methods, vicinal coupling constants combined with extended Karplus equations, which include six coefficients, are applied to a dipeptide model of the amino acid Asp. To find out the empirical chi(1) angles of the side chain, a statistical analysis procedure is developed to compute the rmsd values and find the chi(1) as the minimum of those values. The chi(1) values obtained in this work for nine Asp residues of the flavodoxin protein Desulfovibrio vulgaris are successfully compared with those derived by nuclear magnetic resonance and X-rays.