Ramachandran plot
Generate Ramachandran plots to analyze protein backbone dihedral angles (phi/psi). Visualize favored, allowed, and outlier regions to validate protein structure quality.
Generate Ramachandran plots to analyze protein backbone dihedral angles (phi/psi). Visualize favored, allowed, and outlier regions to validate protein structure quality.
The Ramachandran plot is a two-dimensional visualization of backbone dihedral angles in proteins. Developed in 1963 by G.N. Ramachandran, C. Ramakrishnan, and V. Sasisekharan, it maps the phi (φ) angle against the psi (ψ) angle for each amino acid residue in a protein structure.
The plot reveals which backbone conformations are sterically possible by showing favored, allowed, and outlier regions. Certain angle combinations cause atoms to clash, making those conformations energetically unfavorable. This creates characteristic "allowed" regions that correspond to common secondary structures.
Ramachandran analysis is a standard quality metric in structural biology. High-resolution crystal structures typically show >98% of residues in favored regions. Deviations often indicate errors in structure determination or unusual but functionally important conformations.
The protein backbone contains three types of dihedral angles. The phi (φ) angle describes rotation around the N-Cα bond, while the psi (ψ) angle describes rotation around the Cα-C bond. The omega (ω) angle at the peptide bond is typically fixed at 180° due to partial double-bond character.
The phi angle is calculated from four atoms: C(i-1), N(i), Cα(i), and C(i). The psi angle requires N(i), Cα(i), C(i), and N(i+1). This dependency on neighboring residues means terminal residues cannot have both angles calculated.
Ramachandran's original analysis treated atoms as hard spheres with van der Waals radii. Systematic sampling of all possible φ/ψ combinations revealed that most are sterically forbidden due to atomic clashes. Only specific angle ranges allow the backbone atoms to avoid collision.
The resulting allowed regions correspond directly to protein secondary structures. Alpha helices cluster near φ = -60° and ψ = -45°. Beta sheets occupy the region around φ = -120° and ψ = +120°. Left-handed helices appear in a smaller region with positive phi values.
Different amino acids have distinct allowed regions based on their side chain properties:
Modern Ramachandran analysis uses empirical boundaries derived from high-resolution structures. This tool implements the classification system from Lovell et al. (2003), based on statistical analysis of ~500 high-quality crystal structures:
Each point on the plot represents one residue's φ/ψ angles. Green shaded regions indicate favored conformations; yellow regions show allowed conformations. Points outside colored regions are outliers.
Hover over points to see residue details including name, number, chain, exact angles, and region classification. Use the highlight controls to filter by residue type (general, glycine, proline, pre-proline) or to show only outliers.
The statistics summarize structure quality:
Outliers are listed in a dedicated table with their exact angles. Not all outliers indicate errors. Functionally important residues sometimes adopt strained conformations for catalysis or binding. Compare outlier positions with functional annotations before concluding they represent errors.
Ramachandran analysis serves multiple purposes in structural biology:
Ramachandran plot generation is free and runs entirely in your browser. No credits required.
Based on: Ramachandran GN, Ramakrishnan C, Sasisekharan V. Stereochemistry of polypeptide chain configurations. J Mol Biol. 1963;7:95-99. Region boundaries based on: Lovell SC et al. Structure validation by Cα geometry: φ,ψ and Cβ deviation. Proteins. 2003;50(3):437-450. DOI: 10.1002/prot.10286