Advances in analytical technologies continue to redefine our understanding of biomolecular structure, enabling increasingly precise characterization of complex molecules. One such innovation, Ion Mobility Mass Spectrometry (IM-MS), is emerging as a powerful tool for the structural analysis of peptides. By adding a separation dimension based on molecular shape and size, IM-MS complements conventional mass spectrometry approaches and offers distinct advantages for solving challenging analytical questions.
When ions subjected to an electric field travel through a region containing gas, collision with the gas molecules can alter their speed. Ions undergoing a higher number of collisions have a lower mobility through the buffer gas. The probability of colliding with the gas is related to the collision cross section (CCS) of the molecule and it is influenced by the ions’ size and shape.
Ion Mobility (IM) technologies are designed to separate molecules with different CCS values. When combined with a high-resolution mass analyzer (IM-MS), these systems provide a comprehensive picture of the analytes in the sample, based not only on their molecular weight but also the additional mobility dimension.
This mobility separation is particularly valuable for peptides and proteins: IM-MS can distinguish conformational changes due to subtle differences in complex peptide structure, such as the presence of stereoisomeric amino acids (D and L-forms) (1). Additional examples of the use of IMS to separate out isomeric peptide species include:
Discover how early analytical strategies enabled the structural characterization of human CGRP, a potent vasodilator. This foundational Nature paper offers valuable insights into peptide analysis techniques still relevant today.
Waters Cyclic IMS Mass Spectrometry (cIMS-MS) stands out for its unique circular design that uses the travelling wave ion mobility (TWIM) technology, enabling multi-pass ion separation.
The additional ion-separation mechanism and the versatility in the experimental setup make it a valuable technique for enantiomeric purity assessment, particularly in synthetic peptide development involving stereoisomeric amino acids.
The incorporation of D-amino acids in synthetic peptides, whether intentional or as impurities, can impact peptide function and immunogenicity. cIMS-MS is adept at detecting these subtle structural differences by resolving structural variations that are invisible in traditional MS data. Both FDA and EMA guidelines emphasize impurity analysis in synthetic peptides, with the EMA explicitly referencing stereoisomers in its guidance (4).
Conventional mass spectrometry cannot categorically distinguish peptide sequences that generate identical mass fragment ions, such as standard b and y fragment ions in peptide sequences containing Leucine or Isoleucine. However, integration of ECD fragmentation with cIMS-MS facilitates the definitive identification and localization of these amino acids in the peptide chain through unique fragmentation mechanisms.
Among post-translational modifications (PTMs), glycosylation can be very complex to characterize. One challenging aspect is the precise location of O-glycosylation in a protein chain. The absence of a linear consensus sequence for O-glycosylation in conjunction with it being commonly found in Ser/Thr rich regions of a protein can make precise O-glycosylation site identification very difficult. ECD fragmentation produces meaningful fragment ions that allow clear identification of O-glycosylation sites.
BioPharmaSpec utilizes advanced analytical platforms, including ECD and cIMS-MS to address the most complex peptide characterization challenges. Our scientists apply ECD and ion mobility mass spectrometry as part of an integrated suite of techniques to investigate:
These capabilities are particularly advantageous for peptides incorporating stereoisomers of amino acids or displaying subtle structural variations that demand more than mass data alone for comprehensive analysis.
ECD and Ion Mobility Mass Spectrometry are more than advanced analytical techniques; they offer a window into the structural complexity of peptides and proteins. Partnering with BioPharmaSpec grants access to state-of-the-art instrumentation and scientific expertise to drive deeper understanding and more informed decisions in peptide research.
Contact BioPharmaSpec to discuss how ECD and Ion Mobility Mass Spectrometry can support your drug development.
