Proteomics Guided Discovery of Flavopeptins: Anti-Proliferative Aldehydes Synthesized by a Reductase Domain-Containing Nonribosomal Peptide Synthetase
Yunqiu Chen , Ryan Adam McClure , Yupeng Zheng , Regan James Thomson , and Neil L. Kelleher
J. Am. Chem. Soc., Just Accepted Manuscript
DOI: 10.1021/ja4031193
Publication Date (Web): June 13, 2013
Copyright © 2013 American Chemical Society

Due to the importance of proteases in regulating cellular processes, the development of protease inhibitors has garnered great attention. Peptide-based aldehydes are a class of compounds that exhibit inhibitory activities against various proteases and proteasomes in the context of anti-proliferative treatments for cancer and other diseases. More than a dozen peptide-based natural products containing aldehydes have been discovered such as chymostatin, leupeptin, and fellutamide; however, the biosynthetic origin of the aldehyde functionality has yet to be elucidated. Herein we describe the discovery of a new group of lipopeptide aldehydes, the flavopeptins, and the corresponding biosynthetic pathway arising from an orphan gene cluster in Streptomyces sp. NRRL-F6652, a close relative of Streptomyces flavogriseus ATCC 33331. This research was initiated using a proteomics approach that screens for expressed enzymes involved in secondary metabolism in microorganisms. Flavopeptins are synthesized through a nonribosomal peptide synthetase containing a terminal NAD(P)H dependent reductase domain likely for the reductive release of the peptide with a C-terminal aldehyde. Solid phase peptide synthesis of several flavopeptin species and derivatives enabled structural verification and subsequent screening of biological activity. Flavopeptins exhibited submicromolar inhibition activities against cysteine proteases such as papain and calpain as well as the human 20S proteasome. They also showed anti-proliferative activities against multiple myeloma and lymphoma cell lines.