Elucidation of Sulfoserine Fragmentation Routes and Structures of Key Product Ions

Abstract

Post-translational modifications play a crucial role in regulating protein structure, function, and cellular signaling pathways. Among these modifications, sulfation is an important biochemical process that influences protein–protein interactions and biological activity. The present study aimed to investigate the fragmentation pathways of protonated sulfoserine and to elucidate the structures of the major product ions formed following modification loss. Collision-induced dissociation (CID) experiments revealed two dominant fragmentation channels corresponding to the loss of SO₃ and H₂SO₄, producing fragment ions at m/z 106 and m/z 88, respectively. Infrared multiple photon dissociation (IRMPD) spectroscopy, combined with density functional theory (DFT) calculations at the B3LYP/aug-cc-pVTZ level, was employed to characterize the structures of these fragment ions. The m/z 106 product ion was confirmed to be structurally identical to protonated serine through direct comparison with experimental and theoretical spectra. Structural analysis of the m/z 88 ion demonstrated that it adopts a 2-carboxy-aziridine structure formed via a kinetically controlled fragmentation pathway. The experimental findings showed excellent agreement with theoretical predictions, highlighting the utility of combining ion spectroscopy and computational chemistry for structural elucidation. Furthermore, inter-laboratory comparisons demonstrated the reproducibility and reliability of IRMPD measurements across different instrumental platforms. This work provides detailed mechanistic insight into sulfoserine fragmentation and contributes to a broader understanding of the gas-phase behavior of sulfated biomolecules, facilitating improved interpretation of tandem mass spectrometric data in proteomic studies.

Keywords: Sulfoserine, Fragmentation pathways, Collision-induced dissociation, Infrared multiple photon dissociation, Density functional theory