OBJECTIVELY JUDGING THE QUALITY OF A PROTEIN-STRUCTURE FROM A RAMACHANDRAN PLOT

Motivation: Statistical methods that compare observed and expected dis tributions of experimental observables provide powerful tools for the quality control of protein structures. The distribution of backbone di hedral angles ('Ramachandran plot') has often been used for. such qual ity control, but without a firm statistical foundation. Results: A new and simple method is presented for judging the quality of a protein s tructure based on The distribution of backbone dihedral angles. Inputs to the method al-e 60 torsion angle distributions extracted from prot ein structures solved at high resolution; one for each combination of residue type and tri-state secondary structure. Output for a protein i s a Ramachandran Z-score, expressing the quality of the Ramachandran p lot relative to current state-of-the-art structures.