Mass Spec Roundup: Gold, G-Proteins, and Gray Seals…

Carbonate Ions Reshape Selectivity in Gold CO₂ Catalysis

New research from the Fritz Haber Institute of the Max Planck Society has uncovered how carbonate ions and their radicals subtly control CO₂ electroreduction on gold electrodes – influencing whether carbon dioxide is converted into fuel or lost to competing reactions such as hydrogen evolution.

Electrolytes containing carbonate are widely used in CO₂ electroreduction, yet their molecular role has remained unclear. “However, the role of carbonate anions and the nature of the interfacial hydration layers during CO₂ electroreduction is still poorly understood,” said first author Christopher Kley.

Using operando spectroscopy and complementary mass spectrometry, the team found that carbonate anions organize interfacial water layers on gold, shaping proton movement and charge transfer. First author Ya-Wei Zhou explained: “This allowed us to detect carbonate anion radicals (CO₃•–),” explained first author Ya-Wei Zhou. “Carbonates promote molecular ordering within interfacial hydration layers and the radicals act as proton relay and facilitate charge transfer to gold, accelerating hydrogen evolution.”

Differential mass spectrometry also revealed that carbonate radicals act as a carbon source, producing formaldehyde. Isotope-labelling and modelling further showed that water, not bicarbonate, is the primary proton donor.

“These findings provide a new molecular-level perspective on the competition between CO₂ electroreduction and hydrogen evolution on gold electrodes, prompting a reevaluation of the origin of electrocatalytic selectivity,” said Beatriz Roldán Cuenya.

How Chemerin Receptors Regulate Metabolic Signaling

Researchers have uncovered how the adipokine chemerin interacts with its two receptors to regulate lipid metabolism, inflammation, and insulin sensitivity – offering new molecular insight into conditions such as obesity and metabolic disease. The study, published in Science, resolves long-standing questions about how chemerin’s receptors CMKLR1 and GPR1 cooperate despite their very different signaling behaviors.

Using cryo–electron microscopy to visualize GPR1 bound to chemerin and to either β-arrestin 1 or β-arrestin 2, the team revealed that β-arrestin 1 adopts four distinct binding modes, shifting from a pre-coupled to a fully engaged state. β-arrestin 2, in contrast, binds in a single stable configuration that promotes receptor internalization and signaling. The researchers also showed that cholesterol is essential for GPR1–β-arrestin 2 engagement but not for β-arrestin 1, highlighting a lipid-dependent regulatory step.

To examine how GPR1 behaves in the absence of chemerin, the team solved the structure of the ligand-free GPR1–β-arrestin 1 complex. Here, mass spectrometry was crucial: analysis of the receptor’s C-terminal region revealed a high basal phosphorylation level, explaining why GPR1 undergoes constitutive arrestin recruitment and internalization even without agonist.

The researchers further found that endogenous fatty acids such as palmitoleic acid and palmitic acid enhance binding of inactive GPR1 to β-arrestin 1, promoting scavenging of antagonistic chemerin isoforms. In adipocytes, this activity increases the availability of CMKLR1 to drive lipid metabolism.

Together, the findings provide the first molecular picture of GPR1 as a lipid-regulated scavenger receptor, offering new avenues for targeting chemerin pathways in metabolic inflammation and obesity.

Seal (Milk) of Approval

Gray seal pups have only 17 days to prepare for life in the frigid North Atlantic, and new research shows just how chemically sophisticated their mothers’ milk must be. In a study published in Nature Communications, researchers from the University of Gothenburg report that gray seal milk contains 332 distinct oligosaccharides – around 33% more than those typically found in human breast milk – and that two-thirds of them have never been described before.

“Our analysis shows that gray seal milk is extraordinary,” said senior author Daniel Bojar in a recent press release. “We identified 332 different sugar molecules… some of these molecules had a previously unseen size of 28 sugar units.” These complex carbohydrates support early immune function, shape gut microbial communities, and help pups rapidly mature their digestive systems during the brief lactation period.

Milk collected throughout lactation from wild Scottish gray seals revealed a coordinated shift in sugar composition – mirroring developmental transitions seen in humans. Using high-resolution mass spectrometry, the team structurally characterized 240 of the sugars and showed that some interact with human immune cells, modulating their responses to bacterial and viral threats.

Several newly identified sugars also displayed potent antibacterial properties, suggesting future applications in infant formula, infection prevention, and gut-health therapeutics.

“The study highlights the untapped biomedical potential hidden in understudied wild species,” Bojar said. “We have analyzed milk from ten mammals so far, and we find unique sugar molecules every time.”

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