Biosynthesis of the Bis-Prenylated Alkaloids Muscoride A and B

Abstract

Prenylation is a common step in the biosynthesis of many natural products and plays an important role in increasing their structural diversity and enhancing biological activity. Muscoride A is a linear peptide alkaloid that contain two contiguous oxazoles and unusual prenyl groups that protect the amino-and carboxy-termini. Here we identified the 12.7 kb muscoride (mus) biosynthetic gene clusters from Nostoc spp. PCC 7906 and UHCC 0398. The mus biosynthetic gene clusters encode enzymes for the heterocyclization, oxidation, and prenylation of the MusE precursor protein. The mus biosynthetic gene clusters encode two copies of the cyanobactin prenyltransferase, MusF1 and MusF2. The predicted tetrapeptide substrate of MusF1 and MusF2 was synthesized through a novel tandem cyclization route in only eight steps. Biochemical assays demonstrated that MusF1 acts on the carboxy-terminus while MusF2 acts on the amino-terminus of the tetrapeptide substrate. We show that the MusF2 enzyme catalyzes the reverse or forward prenylation of amino-termini from Nostoc spp. PCC 7906 and UHCC 0398, respectively. This finding expands the regiospecific chemical functionality of cyanobactin prenyltransferases and the chemical diversity of the cyanobactin family of natural products to include bis-prenylated polyoxazole linear peptides.

Eighteen New Aeruginosamide Variants Produced by the Baltic Cyanobacterium Limnoraphis CCNP1324

“…In previously described linear cyanobactins such as virenamide A–C, aeruginosamide B and C, and viridisamide A, Phe 1 was the most commonly identified N -terminal residue [ 12 , 34 ]. In other cyanobactins, position 1 was occupied by Ile [ 28 , 36 ] or Val [ 37 ]. The high residue masses of the unidentified amino acids and a frequent occurrence of aromatic amino acids at N -terminus of AEGs produced by Limnoraphis sp.…”

“…Apart from reversed prenyl as present in AEG671, cyanobactins can also contain a forward prenylated N -terminus (e.g., AEG-A [ 28 ] and virenamide A [ 12 ]), as well as, a forward C-, and reverse prenylated N -terminus (muscoride A [ 36 ]) or forward prenylated both C- and N -termini (muscoride B [ 37 ]).…”

“…Proton and carbon chemical shifts unambiguously showed that the prenyl group in the studied compound was in reverse prenyl, 1, 1-dimethylallyl form. Apart from reversed prenyl as present in AEG671, cyanobactins can also contain a forward prenylated N-terminus (e.g., AEG-A [28] and virenamide A [12]), as well as, a forward C-, and reverse prenylated N-terminus (muscoride A [36]) or forward prenylated both C-and N-termini (muscoride B [37]).…”

Algal neurotoxin biosynthesis repurposes the terpene cyclase structural fold into an N -prenyltransferase

“…Numerous examples exist of prenylation of hydroxyl groups or nucleophilic carbons, but N-prenylation, especially of primary amines, is comparatively rare. The few known reactions include prenylation of primary amines found in adenines (12,13) or in the cyanobactin class of natural products (14,15).…”

Algal Neurotoxin Biosynthesis Repurposes the Terpene Cyclase Structural Fold Into anN-prenyltransferase

“…Several examples exist of aromatic primary amines, such as those found in adenines, serving as sites of prenylation reactions (12,13). However, to our knowledge, the only examples of N-prenylation of an unactivated primary amine are found in the cyanobactin class of natural products (14,15). However, cyanobactin prenyltransferases utilize peptidic substrates, while DabA and KabA employ a free amino acid.…”