A Ramachandran plot (also known as a Ramachandran
diagram or a [φ,ψ] plot), originally developed in 1963 by G. N.
Ramachandran, C. Ramakrishnan and V. Sasisekharan, is a
way to visualize backbone dihedral angles ψ against φ
of amino acid residues in protein structure.
Plot of φ vs. ψ
The conformations of peptides are defined by the values of φ
Each peptide bond has partial double-bond character due to
resonance and cannot rotate.
Three bonds separate sequential C in a polypeptide chain.
The N-C and C – C bonds can rotate, with bond angles
designated φ and ψ respectively. The peptide C-N bond is not
free to rotate.
Other single bonds in the backbone may also be rotationally
hindered, depending on the size and charge of the side chain
Both φ and ψ increases as the carbonyl and amide nitrogen
(respectively) rotate clockwise.
• By convention, both φ and ψ are defined as 00 when the two
peptide bonds flanking that C carbon are in the same plane.
• In a protein, this conformation is prohibited by steric overlap
between an carbonyl oxygen and an amino hydrogen atom.
Ramachandran plot for L-Ala residues.
• Conformations deemed possible are those that involve
little or no steric interference, based on calculations using
known van der Waals radii and bond angles.
• The areas shaded dark blue reflect conformations that
involve no steric overlap and thus are fully allowed.
• Medium blue indicates conformations allowed at the
extreme limits for unfavorable atomic contacts.
• lightest blue area reflects conformations that are
permissible if a little flexibility is allowed in the bond
• Unshaded portion indicates sterically disallowed
values of φ and ψ for various allowed 20 structures
Every type of secondary structure can be completely described by the
bond angles φ and ψ at each residue.
The structure of cytochrome C shows many segments of helix
and the Ramachandran plot shows a tight grouping of φ = -60 and
psi = -45 to -50.
-helix cytochrome C
Similarly, repetitive values in the region of φ = -110 to -140 and ψ =
+110 to +135 give beta sheets. The structure of plastocyanin is
composed mostly of beta sheets; the Ramachandran plot shows
values in the –110, +130 region:
Glycine Ramachandran Plot
Because its side chain, a single hydrogen atom, is small, a Gly residue
can take part in many conformations that are sterically forbidden for
other amino acids.
Proline Ramachandran Plot
The range for Pro residues is greatly restricted because φ is limited by
the cyclic side chain to the range of -35 to -85.
A Ramachandran plot can be used in 2 somewhat different ways.
i. 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.
ii. A second is to show the empirical distribution of datapoints observed in
a single structure in usage for structure validation, or else in a database
of many structures.