A comparison of the α-helix forming propensities and hydrogen bonding properties of serine phosphate and α-amino-γ-phosphonobutyric acid

The ability of serine phosphate (SerP) or α-amino-γ-phosphonobutyric acid (AbuP) and arginine to form a salt bridge between their side chains appears to be much greater when they are spaced i/i+4 than when they are spaced i/i+3. The side chain-side chain interaction between SerP/Arg and AbuP/Arg, positioned i/i+4, contribute 0.45 and 0.62 kcal mol−1, respectively, toward stabilizing the α-helical conformation of a peptide.