Pivot residue: An analysis of domain motion in proteins

In this study, we present an approach to identify some residues that represent the pivot points to experience conformational changes between open (unligand) and closed (ligand) forms of a protein. First, an angle, θ, formed by 4 consecutive Ca atoms in polypeptide backbones was introduced. The difference of this angle, Δθ, from the equivalent residues between the open and the closed form was used to represent the local torsion changes in the protein structure, and the residue with the maximum among Δθ was identified to be a pivot residue. We demonstrate the ability of our method by identifying the pivot residues from five proteins, Lysozyme mutates, Lactoferrin, Lay/Arg/Orn-binding protein, Calmodulin and Catabolit gene activator protein. These pivot residues are located at the hinges in the proteins, they are hinge points for the domain motion. These examples also show that the pivot residues are useful to distinguish the mechanism between shear motion and hinge motion in a protein.