Hansel, S. M. | bioRxiv Science

bioRxiv2025

Discovery of Glycation-Derived Crosslinks at Arginine

Glycation crosslinks account for more than 40% of all known advanced glycation end products (AGEs) and are correlated with many age-related diseases. Despite much interest, crosslinking AGEs (xl-AGEs) remain poorly understood, as they have been challenging to discover, prepare, and quantify. Here we describe a peptide platform that is ideally suited for the study of xl-AGEs, which not only facilitates direct comparisons between the prevalence of known xl-AGEs and other AGEs, but also enables the discovery of previously unknown xl-AGEs. In this study, we use this platform to discover the first known Arg-Arg xl-AGEs, a pair of methylglyoxal-derived dihydroxyimidazolidine hemiacetal crosslink, or MIDAL, isomers. We show that MIDAL can become the major AGE, exceeding levels of all other AGEs, for substrates in which two Arg glycation sites are optimally positioned. We further demonstrate that MIDAL is readily and reversibly generated in biocompatible conditions, persisting with a half-life of more than three days. We also demonstrate that MIDAL can form in living mammalian cells, suggesting that it has the potential to be a dynamic, physiologically relevant and functional xl-AGE. This work therefore offers important insights about MIDAL formation and describes a versatile platform to enable the study of xl-AGEs under a variety of conditions. We expect that it will be highly useful for further discovery of biologically relevant glycation crosslinks that are yet to be identified.

biochemistry↗

bioRxiv2025

A Chemical Mechanistic Path Leads the Way to Cellular Argpyrimidine

Argpyrimidine (APY) is a methylglyoxal-derived advanced glycation end-product (AGE) that has been associated with multiple diseases. As APY forms without an enzyme, it remains exceptionally difficult to pinpoint where APY is likely to be found, both on individual proteins and in cells. In this study, we used a peptide model system and mass spectrometry analysis to investigate the chemical mechanism through which APY arises from methylglyoxal (MGO), a biologically relevant glycating agent. Consistent with other proposed APY formation mechanisms, our results identify AGE species with a mass change of [M+144], presumably including tetrahydropyrimidine (THP), as a direct precursor to APY. However, our results rule out previously proposed reductone or oxidative decarboxylation mechanisms. Instead, we show that a formal oxidation step is not required, and that formate is released instead of CO2. We further show the potential for a nearby residue such as Tyr to assist in the APY formation mechanism by acting as a general base. These experiments also reveal that phosphorylated Tyr or Ser residues can also promote equivalent levels of APY formation, despite introducing additional negative charges that we previously showed to impede glycation. Guided by these mechanistic insights and a newly defined role for phosphorylated residues on glycation substrates, we performed quantitative bottom-up proteomics analysis for MGO-treated cells. Gene ontology analysis for AGE-modified proteins revealed enrichment of phosphorylation-related terms (e.g. kinase activity or protein phosphorylation) for APY, while other Arg post-translational modifications did not. Collectively, these data define a chemical mechanistic path to APY and suggest significant crosstalk between cellular phosphorylation and glycation events including APY formation.

biochemistry↗