Detection and localisation of disulphide bonds in a synthetic peptide reproducing the sequence 1-30 of Par j 1.0101 by electrospray ionisation mass spectrometry

The structural characterisation of a synthetic peptide reproducing the sequ ence 1-30 of Parj 1.0101, a major allergenic protein present in the pollen of Parieta judaica, by combined use of chemical and enzymatic cleavage, rev ersed-phase high-performance liquid chromatography (RP-HPLC) and electrospr ay ionisation mass spectrometry (ESI-MS), is described. Direct ESI-MS of th e synthetic peptide after reaction with methyl iodide showed that the produ ct is a mixture of two peptides: one form in which two out of the four cyst eine residues present in the sequence are oxidised and a minor amount of an other form in which all the cysteines are fully reduced. It was ascertained , using the combined procedure described above and without prior separation of the two species, that the disulphide bond in the partially oxidised for m is located between cysteines 29 and 30. These results show the usefulness of this approach for characterising synthetic peptides containing multiple cysteine residues in the sequence.