Phosphorylation stabilizes the N-termini of alpha-helices

The role of phosphorylation in stabilizing the N-termini of alpha-helices is examined using computer simulations of model peptides. The models comprise either a phosphorylated or unphosphorylated serine at the helix N-terminus, followed by nine alanines. Monte Carlo/stochastic Dynamics simulations were performed on the model helices. The simulations revealed a distinct stabilization of the helical conformation at the N-terminus after phosphorylation. The stabilization was attributable to favorable electrostatic interactions between the phosphate and the helix backbone. However, direct helix capping by the phosphorylated sidechain was not observed. The results of the calculations are consistent with experimental evidence on the stabilization of helices by phosphates and other anions.