SHIFTOR is available as a freely accessible web server at. SHIFTOR exploits many of the recent developments and observations regarding chemical shift dependencies as well as using information in the Protein Databank to improve the quality of its shift-derived torsion angle predictions. The program is also capable of predicting chi1 angles with 81% accuracy and omega angles with 100% accuracy. Overall, the program is 100x faster and its predictions are approximately 20% better than existing methods. Here we describe a program, called SHIFTOR, that is able to accurately predict a large number of protein torsion angles (phi, psi, omega, chi1) using only 1H, 13C and 15N chemical shift assignments as input. The situation could be greatly improved if the determination of all torsion angles (phi, psi, chi and omega) could be made via a single type of measurement (i.e. The dependency on multiple experimental (and computational) methods to obtain different torsion angle restraints is both time-consuming and error prone. Additionally, the efficiency with which these dipolar recoupling experiments suppress. However, many of these techniques measure only one torsion angle or are accurate for only certain classes of secondary structure. Currently most backbone (phi/psi) torsion angles are determined using a combination of J(HNHalpha) couplings and chemical shift measurements while most side-chain (chi1) angles and cis/trans peptide bond angles (omega) are determined via NOEs. Several approaches for utilizing dipolar recoupling solid-state NMR (ssNMR) techniques to determine local structure at high resolution in peptides and proteins have been developed. Regular -polypeptide structures, like the Pauling 3. These restraints may be obtained by J coupling, cross-correlation measurements, nuclear Overhauser effects (NOEs) or secondary chemical shifts. The use of backbone torsion angles as variable parameters permits the analysis of a three-dimensional problem in two-dimensional, torsion angle space. The program relies far more extensively on the use of trained artificial neural networks than its predecessor, TALOS+. Torsion angle restraints are frequently used in the determination and refinement of protein structures by NMR. A new program, TALOS-N, is introduced for predicting protein backbone torsion angles from NMR chemical shifts.
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