Characterization of Novel Oxidation Products of Cysteine in Synthetic Active Site motif HCSAGIGRS of Protein Tyrosine Phosphatase 1B

摘要

The formation of hydroxyl radical (OH~(+)) and H_(2)O_(2) mediated oxidation products of a synthetic peptide, HCSAGIGRS, which is an active site sequence motif of protein tyrosine phosphatase 1B (PTP1B), are investigated. It was determined that a novel cysteine sulfinamide (HC[S(O)N]SAGIGRS) intermediate is produced in the oxidation reaction by Fenton reagents (Fe+2/H2O2) as well as by H_(2)O_(2) and was unambiguously characterized by tandem mass spectrometry experiments on both singly and doubly charged precursor ions. Further, MS3 experiments on an ion trap instrument confirmed that HC[S(O)N]SAGIGRS is not a water loss product of cysteine sulfinic acid [HC(SO_(2)H)SAGIGRS]. In this study, we also probed the formation of cysteine sulfenic acid [HC(SOH)SAGIGRS] and the data obtained from tandem mass spectrometry experiments provided the evidence for the stable existence of cysteine sulfenic acid in solution. A mechanism for the formation of a cysteine sulfinamide intermediate is proposed based on the above experimental results. While there are diverse oxidized species of a cysteine and its oxidation mode to produce them, the preparation and identification of a cysteine sulfinamide intermediate in this study may provide insight into the mechanism of both OH~(+) and H_(2)O(2) induced oxidation reactions of PTPs.