Explain Ramchandran plot. What is its physical significance.
Answers
Two torsion angles in the polypeptide chain, also called Ramachandran angles (after the Indian physicist who worked on modeling the interactions in polypeptide chains, Ramachandran, GN, et al., J Mol Biol, 7:95-99) describe the rotations of the polypeptide backbone around the bonds between N-Cα (called Phi, φ) and Cα-C (called Psi, ψ, see below for the graphics view of the angles). A special way for plotting protein torsion angles was also introduced by Ramachandran and co-authors, and was subsequently named the Ramachandran plot. The Ramachandran plot provides an easy way to view the distribution of torsion angles in a protein structure. It also provides an overview of excluded regions that show which rotations of the polypeptide are not allowed due to steric hindrance (collisions between atoms). The Ramachandran plot of a particular protein may also serve as an important indicator of the quality of its three-dimensional structures (see below).