Localizing Isomerized Residue Sites in Peptides with Tandem Mass Spectrometry.

Area of Science:

• Biochemistry
• Analytical Chemistry
• Proteomics

Background:

• Isomerized amino acid residues are found in biological peptides and can impact biological activity and aging.
• Spontaneous isomerization without mass shift makes identification and localization difficult.
• Current mass spectrometry (MS) methods, particularly MS² spectra, struggle to pinpoint isomerization sites.

Purpose of the Study:

• To develop a fast and efficient method for locating isomerized residues in peptides.
• To overcome the limitations of standard MS² analysis for isomerization site localization.
• To provide an accessible MS-only methodology for identifying isomerized residues.

Main Methods:

• Utilized tandem mass spectrometry (MS) with MS³ experiments to analyze fragment ions.
• Compared MS³ spectra of fragment ions to identify differences indicative of isomerized sites.
• Employed statistical analyses to pinpoint specific MS² fragments containing isomerized residues.

Main Results:

• MS³ experiments successfully localized isomerized residues in peptides, overcoming MS² limitations.
• The method demonstrated compatibility with ion-trap or beam-type collisional activation.
• The approach is suitable for quantifying isomer mixtures and can be coupled with liquid chromatography.

Conclusions:

• A novel MS³-based strategy enables precise localization of isomerized amino acid residues in peptides.
• This MS-only methodology enhances accessibility to critical information about peptide isomerization.
• The findings have implications for research into aging and biological activity influenced by isomerized peptides.