Conformational effects of serine phosphorylation in phospholamban peptides.

We have employed one- and two-dimensional 1H-NMR spectroscopy to study the effects of serine phosphorylation on peptide conformations, using cardiac phospholamban as a model system. The non-phosphorylated phospholamban 1-20 peptide has few restraints on the conformations available to it in aqueous solution. Phosphorylation at Ser16 results in greater constraints being placed on the region encompassing Arg14-Thr17, particularly at neutral pH when the phosphate group is in the di-anionic form. These conformational restrictions arise from specific interactions between the side-chain of Arg14 and the phosphate group. While substitution of phosphothreonine at position 16 causes generally similar effects to phosphoserine, aspartic acid has little effect. The results are compared with phosphorylation effects in other systems, including cardiac troponin I.