Rapid Communications Structure Revision of the Lantibiotic 97518 Sonia I. Maffioli,* ,†,‡ Donatella Potenza, ‡ Francesca Vasile, ‡ Marilenia De Matteo, ‡ Margherita Sosio, † Barbara Marsiglia, ‡ Vincenzo Rizzo, ‡ Carlo Scolastico, ‡ and Stefano Donadio † NAICONS, New Anti-InfectiVe CONSortium, Via G. Fantoli 16/15, 20138, Milan, Italy, and CISI, Centre for Bio-molecular Interdisciplinary Studies and Industrial Applications, Via G. Fantoli 16/15, 20138, Milan, Italy ReceiVed December 15, 2008 The lantibiotic 97518, produced by a Planomonospora sp., was reported as a 2194 Da polypeptide comprising 24 amino acid residues with five thioether bridges. It was assigned to the mersacidin subgroup of type B lantibiotics by Castiglione et al. (Biochemistry 2007, 46, 5884-5897) and named planosporicin. New analytical, chemical, and genetic data and reinterpretation of the published NMR chemical shifts enable structure revision of 97518. The resulting revision of the 97518 structure involves both a shift of two amino acids and a reorganization of two thioether bridges. With this revision, the lantibiotic 97518 becomes a clear member of the nisin subgroup of compounds. Lantibiotics are ribosomally synthesized and post-translationally modified peptides produced by Gram-positive bacteria. 1 They contain the thioether-cross-linked amino acids lanthionines and/or methyllanthionines in addition to 2,3-didehydroalanines (Dha) and/ or (Z)-2,3-didehydrobutyrines (Dhb). On the basis of their structural and functional features, the lantibiotics endowed with antibacterial activity are currently divided into two groups: type A are typically elongated, amphiphilic peptides, while type B are compact and globular. 2 Nisin is the prototype of type A lantibiotics, whereas actagardine and mersacidin belong to the type B subclass. Despite differences in shape and primary structure, both nisin- and mersacidin-type lantibiotics interact with the membrane-bound peptidoglycan precursor lipid II. 3 Lantibiotics have been isolated mostly from the order Firmicutes, while relatively few have been described from the Actinomycetales, with actagardine 4 and the recently described 107891 5 and 97518 (planosporicin) 6 as repre- sentative examples. The lantibiotic 97518, produced by a Planomonospora sp., was reported as a 2194 Da polypeptide consisting of 24 amino acid residues with five thioether bridges. On the basis of the reported structure (1) and mode of action, 97518 was assigned to the type B lantibiotics. The lantibiotics 97518 and 107891, produced by the Planomonospora-related genus Microbispora, represent promising compounds to potentially treat infections caused by multiresistant Gram-positive pathogens. Inspection of the published structure (1) of 97518 highlighted similarity in amino acid sequence to nisin- type lantibiotics, including 107891, despite different thioether linkages. The first 12 residues of nisin fold back into the first two lanthionine rings, forming a cage-like structure that forms five intermolecular hydrogen bonds between the backbone amide functionalities of nisin and the pyrophosphate group. 7 The N- terminal two-ring system is maintained in a number of other lantibiotics, suggesting a common lipid II-interacting fold. In contrast, mersacin-type lantibiotics interact with lipid II through a different fold, proposed to be the highly conserved CTLTXEC propeptide sequence (X any amino acid). 8 The reported structure of 97518 (1) assigns thioether linkages between amino acids 3-11 and 7-18, thus resulting in neither the nisin- nor the mersacidin- type fold. However, the N-terminal 10-aa sequence of the linear precursor shares six identical amino acids with nisin, suggesting that thioether linkages different from those published would result in a nisin-type fold. Data are reported that result in the 97518 structure being revised as 2, thus possessing a new amino acid sequence and two different thioether linkages from the structure 1 published by Castiglione et al. 6 * To whom correspondence should be addressed. Tel: +39 02-50320966. Fax: +39 02-50320919. E-mail: SMaffioli@naicons.com. † NAICONS. ‡ CISI.  Copyright 2009 by the American Chemical Society and the American Society of Pharmacognosy Volume 72, Number 4 April 2009 10.1021/np800794y CCC: $40.75  2009 American Chemical Society and American Society of Pharmacognosy Published on Web 03/20/2009