Native metabolomics identifies pteridines as CutA ligands and modulators of copper binding

CutA, a conserved protein across all domains of life, has long been linked to copper tolerance in Escherichia coli, though recent studies question this association. To clarify its function, we studied cutA knockout mutants from two phylogenetically distant species, E. coli and Synechococcus elongatus PCC 7942, using phenotyping combined with targeted and untargeted metabolomics. Native metabolomics of cell extracts revealed the lumazine dehydroxyxanthopterin B2, a previously uncharacterized pteridine, to bind CutA in both species. Based on these results, we identified other pteridines, including the essential cofactor tetrahydrobiopterin, as ligands of CutA proteins. In the presence of pterins, we observed higher affinity of CutA to copper ions. These findings, alongside the known role of pteridines as redox shuttles, suggest a previously unrecognized role for CutA in coordinating copper homeostasis and redox balance via pteridine metabolism. SignificanceWe identified the molecular class of pteridines as natural ligands of CutA, including the so far unknown lumazine dehydroxyxanthopterin B2. Pteridines are known redox shuttles involved in various cellular processes such as cofactors for redox enzymes. Our data showed increased copper binding to CutA in the presence of pteridines. Together, these results suggest that pteridines are physiological ligands of CutA that may modulate copper binding and redox homeostasis.