Résumé
Albicidin is a potent DNA gyrase inhibitor produced by the sugarcane pathogenic bacterium Xanthomonas albilineans. It blocks the d ifferentiation of chloroplasts, resulting in appearance of narrow white stripes on sugarcane leaves that are characteristic of leaf scald d isease. Albicidin targets the bacterial gyrase by a mechanism that is different from the one of any other known DNA gyrases inhibitors [l]. It exhibits antibacterial activity at nanomolar concentrations against Escherichia coli and to a lower extent aga inst numerous human pathogenic bacteria [2]. A decade of intense work was necessary to decipher a lbicid in's biosynthetic pathway and to elucidate its astonishing never-seen-before structure. Albicidin is produced by a hybrid PKS/NRPS system. Such ribosome-independent systems cons ist of modular megasynthetases which operate in an assembly-line fashion to activate, modify and link mostly unusual aminoacid build ing blocks, fina lly resulting in complex bioactive peptide-like molecules. The structure of albicidin, which was predicted by fo rmer in silico sequence a nalyses of its PKS/ NRPS gene cluster [3], was ascertained by means of mass spectrometry and NMR spectroscopy. We demonstrated that a lbicidin exhibits a linear polyaromatic penta-peptidic structure containing the rare aminoacids para-aminobenzoate a nd cyanoalanine [4]. Insights into biosynthesis and structure of natural a nalogues of al bicidin will also be presented [5]. The determination of the structure of albicidin allowed the development of a protocol for the chemical synthesis of this complex molecule [6]. Consequently, new research, such as structureactivity relationship studies, will now be possible. (Résumé d'auteur)