Biosynthesis and ecological functions of diketopiperazine natural products from marine actinomycetes

Molecules featuring 2,5-diketopiperazine (DKP) scaffolds are common in Nature and have been isolated from a variety of fungi and bacteria. These cyclodipeptides offer a range of medicinal activities, including antimicrobial, anticancer, and immunosuppressant effects. Cyclodipeptide synthases (CDPSs) were recently revealed as a novel family of small (˜30 kDa) enzymes that assemble DKPs from aminoacyl-tRNA substrates diverted from primary metabolic pathways. Although bioinformatics analyses of microbial genomes suggest that CDPSs are widespread amongst terrestrial and marine bacteria, fewer than a dozen CDPSs have been biochemically characterized. Here, we present the biochemical characterization of two CDPSs from a marine-derived Nocardiopsis sp. actinomycete. Our data reveal that both of these phylogenetically distinct CDPSs are highly selective for tryptophan-charged tRNA substrates to yield exclusively cyclo(L-Trp-L-Trp). We also present results from field and laboratory experiments probing cyclo(L-Trp-L-Trp) and other microbial DKPs as mediators of interactions between marine microorganisms. Together, our data provide insights into the prevalent, yet understudied CDPS enzyme family and suggest important adaptive functions of corresponding DKP metabolites.