Discovered in the 1990s as a product of the metabolism of the so-called ‘rare’ filamentous actinomycete Actinomadura lepetitiana DSM 10909 [1], GE23077 is a non-ribosomally synthesised cyclic heptapeptide antibiotic that inhibits a wide range of bacterial RNA polymerases (RNAP) in vitro while not affecting mammalian enzymes [2]. After its discovery, the molecule was later overlooked due to its more limited in vivo antimicrobial activity, which has mainly been exerted against Moraxella catarrhalis, Neisseria gonorrhoeae, and Mycobacterium smegmatis isolates [3]. However, with an increasing number of bacteria becoming resistant to antibiotics, including the major currently approved RNAP inhibitors (i.e., fidaxomicin and rifamycin), the development of new drugs to fight bacterial infections is essential. In this context, GE23077 might prove promising, as its target includes functionally critical residues of the RNAP that are different from those targeted by other inhibitors [4].
Therefore, our collaborative project aims to better understand the production of GE23077 using multiple approaches as an essential step for its further development. A high-quality genome sequence of A. lepetitiana was recently obtained using Illumina MiSeq and MinION, followed by the identification and annotation of a putative biosynthetic gene cluster (BGC) for the production of GE23077. Following the development of new methods for the genetic manipulation of this recalcitrant actinomycete, knock-out studies of key genes in the BGC and overexpression studies of two putative regulatory genes are currently ongoing. In parallel, in vitro studies are being performed on purified A. lepetitiana RNAP to evaluate its susceptibility to GE23077.
Elucidating the mechanisms behind the synthesis of this promising RNA inhibitor may also open the way to combinatorial biochemistry approaches to modify the molecule and potentially improve its in vivo antimicrobial activity.
[1] Dalmastri et al. Int J Syst Evol Microbiol 2020, 70(8):4782-90. [2] Ciciliato et al. J Antibiot 2004, 57(3):210-17. [3] Sarubbi et al. Eur J Biochem 2004, 271(15):3146-54. [4] Zhang et al. eLife 2014, 3:e02450.
