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. Author manuscript; available in PMC: 2019 Aug 19.
Published in final edited form as: Science. 2019 Jul 19;365(6450):280–284. doi: 10.1126/science.aau6232

Figure 4. Ammosamide biosynthesis involves addition of L-Trp to the C-terminus of a ribosomally synthesized peptide.

Figure 4.

(A) Pyrolloquinoline alkaloids ammosamides A-C. (B) Sequence alignment of the C-terminus of the AmmA precursor peptide and its homologs showing a C-terminal extension for AmmA relative to most homologs. The gene cluster for ammosamide biosynthesis in Streptomyces sp. CNR698 comprises 27 orfs. The encoded proteins include four small LanBs, two proteases, one halogenase and a transporter. (C) AmmB2 adds L-Trp to AmmA*, a truncated peptide of AmmA, to afford AmmA*W in vitro in an ATP, tRNATrp and Trp-RS dependent reaction. Red MALDI-TOF mass spectrum is AmmA* and the blue spectrum shows the product of the reaction. HR-ESI MS/MS confirms addition of L-Trp to the C-terminus.