Biology subjects

Scheck, R. A.

Publications and source records attributed to Scheck, R. A..

4 recordsLinked to original sources

bioRxiv2025

A Cyclic Arginine Adduct Eclipses Carboxymethylation as the Primary Glyoxal-Derived Advanced Glycation End-Product

Glyoxal (GO) is a highly reactive 1,2 dialdehyde implicated in the formation of a set of disease-associated post-translational modifications (PTMs) known as advanced glycation end products (AGEs). While GO has been widely reported to modify lysine to form the highly studied AGE carboxymethyllysine (CML), here we demonstrate that GO alone leads to highly chemoselective arginine glycation, yielding a stable glyoxal-derived hydroimidazolidine (GH-DH) product. This near-exclusively formed AGE has the same mass change as carboxymethylarginine (CMA), which implies that it may have been overlooked or misattributed in prior studies. In contrast, lysine modification by GO is highly dependent on the presence of hydride-based reducing agents, suggesting that prior reports may have artifactually generated CML through pervasive use of reductive amination protocols during sample preparation. These findings challenge the standing assumptions about the landscape of GO-derived glycation, emphasizing the importance of carefully considering the impact of experimental conditions in glycation studies. By redefining the complement of GO-derived AGEs, this study provides essential new information that is greatly needed for uncovering their biology, creating new tools for their study, and discovering therapies that ameliorate or mitigate their glycation-related damage.

biochemistry↗

bioRxiv2025

Predictable modulation of a spontaneous post-translational modification in living cells

Glycation is a non-enzymatic post-translational modification associated with aging and disease. Because it occurs spontaneously, it is extremely difficult to control the extent of glycation at distinct sites within target proteins, especially in cellular systems. Here we report a chemical approach, referred to as dialAGE, that enables the site-specific control of protein glycation. This unique tool requires the introduction of just a single point mutation that modulates the glycation susceptibility of a nearby arginine. As proof-of-concept, extensive mass spectrometry analysis was performed to confirm that dialAGE can modulate site-specific glycation levels at multiple arginine residues in ubiquitin in vitro, enabling both enhanced and diminished glycation. Introduction of dialAGE point mutations and/or glycation with the biologically relevant glycating agent methylglyoxal did not affect polyubiquitin chain formation using in vitro ubiquitination assays. Furthermore, we show that dialAGE can be used to modulate ubiquitin glycation levels in living mammalian cells. We therefore anticipate that this method will be particularly useful for enabling the study of glycation as a genuine, functional, post-translational modification.

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↗

bioRxiv2021

Members of the Legionella pneumophila Sde Family Target Tyrosine Residues for Phosphoribosyl-Linked Ubiquitination

Legionella pneumophila establishes a replication vacuole by translocating hundreds of protein effectors through a type IV secretion system (T4SS). Among these translocated effectors are members of the Sde family, which catalyze phosphoribosyl-linked ubiquitination (pR-Ub) of host targets. Previous work has posited that Sde proteins solely target serine (Ser) residues within acceptor protein substrates. We show here that SdeC-mediated pR-Ub modification results from a stepwise reaction that also modifies tyrosine (Tyr) residues. Unexpectedly, the presence of an HA tag on Ub resulted in poly-pR-ubiquitination, consistent with the HA tag acting as an acceptor target. Interrogation of phosphoribosyl-linked HA-Ub revealed that Tyr4 was the preferred targeted residue, based on LC-MS/MS analysis of the crosslinked product. Further analysis using synthetic HA variants revealed promiscuous modification of Tyr, as crosslinking was prevented only by constructing a triple mutant in which all three Tyr within the HA sequence were substituted with Phe. Although previous work has indicated that Ser is the sole acceptor residue, we found no evidence of Ser preference over Tyr using Tyr->Ser replacement mutants. This work demonstrates that pR-ubiquitination by the Sde family is not limited to Ser-modification as previously proposed, and broadens the potential sites targeted by this family.

biochemistry↗