Ramachandran plot by Krunal Chodvadiya
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Transcript of Ramachandran plot by Krunal Chodvadiya
Ramachandran plot
ByKrunal Chodvadiya10MBT001
Ramachandran plot
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 and ψ.
Each peptide bond has partial double-bond character due to resonance and cannot rotate.
Three bonds separate sequential Ca in a polypeptide chain. The N-Ca and Ca– 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 R groups.
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 Ca 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 angles.
• Unshaded portion indicates sterically disallowed conformations
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 -a helix and the Ramachandran plot shows a tight grouping of φ = -60 and psi = -45 to -50.
a-helix cytochrome CRamachandran plot
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:
beta-sheet plastocyanin Ramachandran plot
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.
Significance 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.
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