Biosynthesis of 14-Membered Cyclopeptide Alkaloids via Nonheme Iron- and 2‑Oxoglutarate-Dependent Oxidative Decarboxylation

Cyclopeptide alkaloids are an expanding class of plant
peptide
natural products defined by a macrocyclic ether cross-link via a tyrosine-derived
phenol. Classical cyclopeptide alkaloids are characterized by strained
13- to 15-membered cyclophanes and terminal modifications such as N-methylation and C-terminal styrylamine moieties. While
synthetic access to many classical cyclopeptide alkaloids has been
established, no biosynthetic route has been reported. Here, we elucidate
the biosynthetic pathway of a 14-membered cyclopeptide alkaloid, lotusine
A, from the Chinese date tree (Ziziphus jujuba), which features peptide cyclization on a ribosomal precursor peptide
by a split burpitide cyclase, nonheme-iron and 2-oxoglutarate-dependent
oxidative decarboxylation affording the C-terminal hydroxystyrylamine,
and SAM-dependent N-terminal α-N,N-dimethylation.
We apply the discovered Z. jujuba enzymes
in combination with a clubmoss cyclopeptide alkaloid cyclase for the
biosynthesis and diversification of the analgesic adouetine X and
the anxiolytic sanjoinine A by combining in planta and in vitro reactions. Our work expands the biocatalytic
repertoire of nonheme iron- and 2-oxoglutarate-dependent enzymology
to oxidative peptide decarboxylation and primes scaled metabolic engineering
and chemoenzymatic synthesis of 14-membered cyclopeptide alkaloids
with terminal posttranslational modifications.