Spontaneous chemical modifications like deamidation and isomerization play crucial roles in human diseases and aging by affecting proteins. While high-resolution mass spectrometry has helped identify deamidation sites, characterizing isomerization products remains a challenge. A recent liquid chromatography/mass spectrometry-based approach has shown promise in characterizing the isomeric products of Gln deamidation by using diagnostic fragments to identify Glu and isoGlu. This technique allows simultaneous detection of both isomeric forms and pinpoints the location of the modified residue, showcasing its utility in studying aging of glutamine-containing peptides. The comparison between Gln deamidation and well-studied asparagine deamidation reveals interesting insights.
Asparagine and Gln are amino acids prone to spontaneous deamidation, affecting protein function and implicated in various diseases like Alzheimer’s and cataracts. While asparagine deamidation has been extensively studied, Gln deamidation remains relatively unexplored, despite its biological significance in long-lived proteins like eye lens crystallins. The mechanism of Gln deamidation is hypothesized to be analogous to that of asparagine deamidation, potentially yielding four Glu isomers. The identification of these isomers requires advanced techniques like radical-directed dissociation and mass spectrometry due to the difficulty in distinguishing them based solely on mass shifts.
Aging studies have shown that Gln deamidation is a slow process compared to asparagine deamidation. The use of ammonia accelerant has shed light on the kinetics of Gln deamidation, revealing that direct hydrolysis may play a more significant role in Gln deamidation than previously thought, especially in sequences lacking QG motifs. Through innovative approaches like radical-directed dissociation, the identification and quantification of Glu and isoGlu in aged samples have become feasible, offering new insights into the aging processes of proteins containing glutamine residues.
The comparison between Gln and Asn deamidation highlights key differences in their isomer distributions, with Gln peptides showing more variability influenced by primary sequence. Direct hydrolysis competes with glutarimide ring formation in Gln deamidation, impacting the distribution of isomers formed. While isoGlu formation is sequence-dependent, techniques like radical-directed dissociation enable precise identification of Glu and isoGlu, aiding in the understanding of the aging processes of proteins rich in glutamine residues. The insights gained from these studies can have implications in understanding age-related diseases and designing effective biological therapeutics.
Takeaways:
– Innovative approaches like radical-directed dissociation are pivotal in characterizing isomeric products of Gln deamidation.
– Gln deamidation kinetics differ from asparagine deamidation, with direct hydrolysis playing a significant role.
– Sequence-dependent factors influence the distribution of Glu and isoGlu in Gln deamidation.
– Understanding the aging processes of proteins containing glutamine residues can offer valuable insights into age-related diseases and therapeutic design.
Tags: chromatography, mass spectrometry
Read more on pmc.ncbi.nlm.nih.gov
