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 (<i>mus</i>) biosynthetic gene clusters from <i>Nostoc</i> spp. PCC 7906 and UHCC 0398. The <i>mus</i> biosynthetic gene clusters encode enzymes for the heterocyclization, oxidation, and prenylation of the MusE precursor protein. The <i>mus</i> 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 <i>Nostoc</i> 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.