Structural and Functional Analyses of PolyProline-II helices in Globular Proteins

PolyProline-II (PPII) helices are defined as a continuous stretch of a protein chain in which the constituent residues have the backbone torsion angle ({varphi},{psi}) values of (-75{degrees}, 145{degrees}) and take up extended left handed conformation, lacking any intra-helical hydrogen bonds. They are found to occur very frequently in protein structures with their number exceeding that of {pi}-helices, though it is considerably less than that of -helices and {beta}-strands. A relatively new procedure, ASSP, for the identification of regular secondary structures using Ctrace identifies 3597 PPII helices in 3582 protein chains, solved at resolution [≤] 2.5[A]. Taking advantage of this sign