Ramachandran plot

For instance, the small strip of allowed values along the lower-left edge of the plot are a continuation of the large, extended-chain region at upper left.

One is to show in theory which values, or conformations, of the ψ and φ angles are possible for an amino-acid residue in a protein (as at top right).

The first Ramachandran plot was calculated just after the first protein structure at atomic resolution was determined (myoglobin, in 1960[6]), although the conclusions were based on small-molecule crystallography of short peptides.

Such a clustering is alternatively described in the ABEGO system, where each letter stands for α (and 310) helix, right-handed β sheets (and extended structures), left-handed helixes, left-handed sheets, and finally unplottable cis peptide bonds sometimes seen with proline; it has been used in the classification of motifs[14] and more recently for designing proteins.

The Molecular Biophysics Unit at Indian Institute of Science celebrated 50 years of Ramachandran Map[17] by organizing International Conference on Biomolecular Forms and Functions from 8–11 January 2013.

Original hard-sphere, reduced-radius, and relaxed-tau φ,ψ regions from Ramachandran, with updated labels and axes
Backbone dihedral angles φ and ψ (and ω). All three angles are at 180° in the conformation shown
A Ramachandran plot generated from human PCNA , a trimeric DNA clamp protein that contains both β-sheet and α-helix ( PDB ID 1AXC). The red, brown, and yellow regions represent the favored, allowed, and "generously allowed" regions, respectively, as defined by ProCheck