Assignment of protein backbone resonances using connectivity, torsion angles and 13Cá chemical shifts

A computer program is presented that will return the most probable sequence location for a short connected set of residues in a protein given just 13 C á chemical shifts (ä C á ) and data restricting the phi and psi backbone angles. Data taken from both the BioMagResBank and the Protein Data Bank were used to create a probability density function (PDF) using a multivariate normal distribution in ä C á , . , and ø space for each amino acid. Extracting and combining probabilities for particular amino acids in a short proposed sequence yields a score indicative of the correctness of the proposed assignment. The program is illustrated using several proteins for which structure and 13 C á chemical shift data are available.