Covalent structure of mutacin 1140 and a novel method for the rapid identification of lantibiotics

Abstract

The primary structure of the Streptococcus mutans lantibiotic mutacin 1140 was elucidated by NMR spectroscopy, mass spectrometry, and chemical sequencing. The structure is in agreement with other closely related lantibiotics, such as epidermin. A novel method was developed in which mutacin 1140 was chemically modified with sodium borohydride followed by ethanethiol, allowing the differentiation of the thioethercontaining residues from the dehydrated residues. This double-labeling strategy provides a simple method to reliably identify all modified lantibiotic residues with a minimal amount of material. While NMR spectroscopy is still required to obtain thioether bridging patterns and thus the complete covalent structure, the double-labeling technique, along with mass spectrometry, provides most of the information in a fraction of the time required for a complete NMR analysis. Thus, with these new techniques lantibiotics can be rapidly characterized.Keywords: bacteriocin; double-labeling; mass spectrometry; NMR; structure determination.Mutacin 1140, a member of a family of ribosomally synthesized peptide antibiotics called lantibiotics (lanthioninecontaining antibiotics [1]), is produced by the Gram-positive bacterium Streptococcus mutans [2,3]. Because bacterial resistance to antibiotics is rapidly spreading, new antibiotics are in great demand. Mutacin 1140 has been shown to be stable, highly potent, and to inhibit a broad array of Gram-positive bacteria, including many that are responsible for human diseases [3±5]. Importantly, genetically stable resistant variants of sensitive strains have not yet been found, suggesting that the structure and chemistry of mutacin 1140 may provide important information for the development of new antibiotics. In addition, mutacin 1140 is a key feature in the development of replacement therapy for the prevention of dental caries. A genetically engineered effector strain of S. mutans has been constructed that has decreased virulence due to a mutation in the gene for lactate dehydrogenase [6]. By virtue of its ability to produce three-fold elevated amounts of mutacin 1140, this strain has been shown to displace disease-causing strains of S. mutans from the teeth of experimental animals and thereby provide lifelong protection against tooth decay. Thus, for these several reasons, it is important to obtain a comprehensive understanding of mutacin 1140.In a previous study, Hillman and coworkers reported the genetic and biochemical analysis of mutacin 1140 [3]. In this work, they isolated the mutacin 1140 gene cluster, determined the spectrum of antibacterial activity, characterized a mutant strain of S. mutans (DM25) deficient in antibacterial activity, and reported the isolation and purification of mutacin 1140. Hillman's group also presented a tentative structure of mutacin 1140 [3]. This tentative structure was based primarily on Edman sequencing and mass spectrometry, but the authors noted that``(the thioether bridge) assignment [would] have to be resolved, most probably by nuclea...

Carboxyl Analogue of Mutacin 1140, a Scaffold for Lead Antibacterial Discovery

“…Therefore, the formation of the lanthionine rings needed to be assessed by another method. A rapid and straightforward Edman sequencing method was developed by our group to distinguish between dehydrated residues and dehydrated residues involved in lanthionine ring formation (37). Dehydrated residues are first hydrated by sodium borohydride before lanthionine ring derivatization by an organothiol compound.…”

“…Edman sequencing has been frequently used to determine the sequence of small biological peptides and lantibiotics (54,55). mu1140-COOH was doubly labeled as previously described for mutacin 1140 (37). One nanomole of mu1140-COOH in 5 l of water was added to a reaction tube containing 2 mg of sodium borohydride.…”

Biosynthesis and Transport of the Lantibiotic Mutacin 1140 Produced by Streptococcus mutans

“…The crude extract was run on either a semiprep C 18 column (octyldecyl silane [C 18 ]; particle size, 5 m; 4.6 by 250 mm; Agilent Zorbax) or an analytical column, as previously reported (35). 2-Mercaptoethanol (BME) modification of mutacin 1140 peptide variants was done as previously reported (13,36). The lack of PTM cyclase activity would prevent lanthionine ring formation and result in the presence of cysteine thiols that can be selectively labeled.…”

N‐terminal acetylation in paenibacillin, a novel lantibiotic

“…In summary, the data obtained at this stage confirms the MS/ MS results and addresses the previously reported ambiguities [3], except the putative N-terminal residue. Virtually all of the expected resonances have been assigned (Table 1) with chemical shifts generally close to random-coil values of respective natural or modified amino acids [5][6][7][10][11][12]. Considering that the cyclic ring structural entities are intertwined and account for half of the residues in A11-K30 stretch, the conformation of the C-terminal part is expected to be extremely rigid.…”

“…6d) [10]. As for the bridging topology, the two Lan and three MeLan structures expected from 3 Abu and 7 A were deduced from intra-bridge NOE assignments, between Abu H a and A H b1,b2 in MeLan, and between H N of one A moiety and H b,b2 across the sulfur atom in Lan [11] (Fig. 5).…”