Serine O-sulfation probed by IRMPD spectroscopy

Area of Science:

• Analytical Chemistry
• Biochemistry
• Spectroscopy

Background:

• Amino acid sulfation is a common post-translational modification.
• Its labile nature poses challenges for mass spectrometry-based characterization in proteomics.
• Understanding the structure and stability of modified amino acid ions is crucial.

Purpose of the Study:

• To investigate the O-sulfation of l-serine.
• To elucidate the structural and stability effects of protonation and deprotonation on sulfated serine ions ([sSer + H](+) and [sSer - H](-)).
• To identify diagnostic spectral signatures for sulfation using IRMPD spectroscopy.

Main Methods:

• Electrospray ionization to generate gaseous, isolated ions.
• Isolation and trapping of ions in a Paul ion-trap.
• Infrared multiple photon dissociation (IRMPD) spectroscopy in fingerprint and stretching regions.
• Computational analysis (M06-2X/6-311+G(d,p)) to interpret experimental spectra.

Main Results:

• IRMPD spectra of sulfated serine ions ([sSer + H](+) and [sSer - H](-)) show distinct signatures compared to native serine ions.
• Protonated ions ([sSer + H](+)) are stabilized by hydrogen bonding between the amino group and sulfate/carbonyl oxygens.
• [sSer - H](-) ions exhibit a negatively charged sulfate group involved in S=O···HN or S=O···HO hydrogen bonds.
• Experimental data suggest a population of multiple low-lying conformers for [sSer - H](-) ions.

Conclusions:

• IRMPD spectroscopy effectively identifies O-sulfation of l-serine in gaseous ions.
• Protonation and deprotonation significantly influence the structure and stability of sulfated serine ions.
• Computational modeling aids in interpreting experimental spectra and understanding ion conformations and hydrogen bonding.