Structure elucidation and discrimination of peptides epimers induced by chiral residue by ion mobility mass spectrometry

Background

The chirality of amino acid residues in peptide or protein affects the biological activity and function. Improving the elucidation and discrimination of peptide epimers induced by chiral residues in different positions is of great significance in the physiological and pathological study of the dominant L-chiral protein biosphere. The characterization of peptide epimers have been and remain a challenging task because chiral residues do not cause any change in the physical and chemical properties, such as sequence, isoelectric point, or mass-charge ratio.

Result

In this work, we provide ion mobility mass spectrometry (IM-MS) analysis of peptide epimers induced by chiral residue and further develop a general and efficient strategy for constructing non-covalent complexes with cucurbituril (CB) to achieve epimers discrimination, especially with limited resolving power of most current instruments. Specifically, IM-MS analysis probes the conformational landscape profile from the model methionine enkephalin (ME) epimers, oligomers, metal adjuncts to multi-nary complexes, improving the identification by amplify structural differences and enrich conformational features, in which [ME+CB[8]+Li+H]²⁺ enables simultaneous acquisition of the unique conformational feature of all ME epimers. The structural stability changes from epimers to complexes were characterized by energy resolved MS₂, and further DFT calculations demonstrated the effect of non-covalent interaction on conformational differences, providing insights for molecular recognition.

Significance

The method has been successfully applied to the identification of peptide epimers in neuropeptides with single chiral residue and amyloid truncated peptides with multiple chiral residues. This work provides possibility for rapid discovery and efficient identification of peptide isomers and method support for the establishment of comprehensive biomolecular collision cross section (CCS) database.