SERUM STABILITY OF PHOSPHOPEPTIDES

Synthetic phosphopeptides are increasingly used to mimic phosphoprotei n fragments and in rational drug design. Both applications require a s tudy of the stability of phosphopeptides in biological environments. H ere we report a study of the stability of three sets of synthetic un-, mono-, and diphosphorylated peptides in diluted human serum. The synt hetic peptides contained the phosphoserines or phosphothreonines in mi d-chain position corresponding to immunodominant regions of abnormally hyperphosphorylated variants of the human tau protein present in the paired helical filaments of Alzheimer's disease. The peptide degradati on in humar, serum was monitored, and the first metabolites formed wer e collected from reversed-phase high performance liquid chromatography (RP-HPLC). Seven of nine monophosphorylated peptides exhibited increa sed stability compared to the unphosphorylated parent analogs. All pep tides phosphorylated at immunodominant sites displayed higher serum st ability than phosphopeptide isomers of the same sequences giving evide nce of the extended presence of the antigenic stimulus in the hosts. A nalysis of the degradation pathway of the fastest degrading peptide fa mily showed that the mono-and diphosphorylated peptides, like the unph osphorylated version, underwent aminopeptidase cleavage and the phosph ate group remained attached to the serine and threonine side chains. T hese results indicate that phosphopeptides are suitable models of phos phoprotein fragments in biochemistry assays, and that phosphorylation can be a viable modification of peptide leads in drug design. (C) 1997 Elsevier Science B.V.