Discovery and Assembly-Line Biosynthesis of the Lymphostin Pyrroloquinoline Alkaloid Family of mTOR Inhibitors in Salinispora Bacteria

Abstract

The pyrroloquinoline alkaloid family of natural products that includes the immunosuppressant lymphostin has long been postulated to arise from tryptophan. We now report the molecular basis of lymphostin biosynthesis in three marine Salinispora species that maintain conserved biosynthetic gene clusters harboring a hybrid nonribosomal peptide synthetase-polyketide synthase central to lymphostin assembly. Through a series of experiments involving gene mutations, stable isotope profiling, and natural product discovery, we report the assembly line biosynthesis of lymphostin and nine new analogues that exhibit potent mTOR inhibitory activity.

Diversity and evolution of secondary metabolism in the marine actinomycete genus Salinispora

“…Only nine of these OBUs have been formally linked to the production of specific secondary metabolites. These are sal (salinosporamides) (30), slm (salinilactam) (23), cyl (cyclomarins) (31), cya (cyanosporasides) (28), spo (sporolides) (29), arn (arenimycin) (32), rif (rifamycins) (33), lym (lymphostin) (34), and lom (lomaiviticin) (35), whereas two others are predicted to yield enterocin (36) (PKS31) and arenicolide (37) (PKS28) based on bioinformatic analyses. Although there is no evidence that all pathways are functional, the 113 remaining OBUs far exceed the four Salinispora secondary metabolites (arenamides, pacificanones, salinipyrones, and saliniquinones) that have yet to be linked to specific pathways, suggesting that considerable chemical diversity remains to be discovered from this genus.…”

The marine actinomycete genus Salinispora: a model organism for secondary metabolite discovery

“…126 , and belongs to the diverse class of pyrroloquinoline natural products. The molecular basis for lymphostin biosynthesis has been determined via interrogation of the lym gene cluster, which includes a uniquely organized modular synthetase 127 . Fermentation studies designed to induce lymphostin production also yielded the new derivative lymphostinol ( 62 ) along with the eight additional analogues neolymphostin A–D ( 63-66 ) and neolymphostinol A–D ( 67-70 ).…”

Biosynthetic Pathway Connects Cryptic Ribosomally Synthesized Posttranslationally Modified Peptide Genes with Pyrroloquinoline Alkaloids

“…In 2011, we verified the role of tryptophan in lymphostin biosynthesis and reported on the end-stage biosynthetic events leading to the production of lymphostin in three sequenced strains of the genus Salinispora . (Miyanaga et al, 2011) In that work, the O -methylation and two-carbon malonyl extension were attributed to the SAM-dependent methyltransferase LymB and the hybrid non-ribosomal peptide synthetase-polyketide synthase (NRPS-PKS) LymA, respectively. But there was no indication that neighboring genes at the lym genetic locus were responsible for the production of the pyrroloquinoline core.…”