Serine and β‐turns

Serine is one of the most frequent residues included within β‐turns in proteins. Conformational investigations have been carried out on the LL and LD model dipeptides ButCO‐Pro‐Ser‐NHMe in the solute state by ir and nmr spectroscopies and in the solid state by x‐ray diffraction. LL and LD sequences are folded in the βI‐ and βII‐types, respectively, and in both cases a weak intramolecular interaction takes place between the NH and Oγ sites of the serine residue.