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Proteusins are a family of bacterial ribosomal peptides that largely remain hypothetical genome‐predicted metabolites. The only known members are the polytheonamide‐type cytotoxins, which have complex structures due to numerous unusual posttranslational modifications (PTMs). Cyanobacteria contain large numbers of putative proteusin loci. To investigate their chemical and pharmacological potential beyond polytheonamide‐type compounds, we characterized landornamide A, the product of the silent osp gene cluster from Kamptonema sp. PCC 6506. Pathway reconstruction in E. coli revealed a peptide combining lanthionines, d‐residues, and, unusually, two ornithines introduced by the arginase‐like enzyme OspR. Landornamide A inhibited lymphocytic choriomeningitis virus infection in mouse cells, thus making it one of the few known anti‐arenaviral compounds. These data support proteusins as a rich resource of chemical scaffolds, new maturation enzymes, and bioactivities. [ABSTRACT FROM AUTHOR]

Proteusins are a family of bacterial ribosomal peptides that largely remain hypothetical genome‐predicted metabolites. The only known members are the polytheonamide‐type cytotoxins, which have complex structures due to numerous unusual posttranslational modifications (PTMs). Cyanobacteria contain large numbers of putative proteusin loci. To investigate their chemical and pharmacological potential beyond polytheonamide‐type compounds, we characterized landornamide A, the product of the silent osp gene cluster from Kamptonema sp. PCC 6506. Pathway reconstruction in E. coli revealed a peptide combining lanthionines, d‐residues, and, unusually, two ornithines introduced by the arginase‐like enzyme OspR. Landornamide A inhibited lymphocytic choriomeningitis virus infection in mouse cells, thus making it one of the few known anti‐arenaviral compounds. These data support proteusins as a rich resource of chemical scaffolds, new maturation enzymes, and bioactivities. [ABSTRACT FROM AUTHOR]