Lantibiotic Biosynthesis: Interactions between Prelacticin 481 and Its Putative Modification Enzyme, LctM

Abstract

Class AII and AIII lantibiotics and mersacidin are antibacterial peptides containing unusual residues obtained by posttranslational modifications of prepeptides, presumably catalyzed by LanM. LctM, the LanM for lacticin 481, is essential for the production of this class AII lantibiotic. Using the yeast two-hybrid system, we showed direct contact between the prelacticin 481 and LctM, supporting the proposed LctM function. Sixteen domains are conserved between the 10 known LanM proteins, whereas three additional domains were found only in class AII LanM proteins and in MrsM, the LanM for mersacidin. All the truncated LctM proteins that we tested presented impaired LctA-binding activity.Bacteriocins are ribosomally synthesized peptides with antibacterial activity. Some bacteriocins from gram-positive bacteria are termed lantibiotics because they present the unique feature of containing unusual residues, leading to intramolecular thioether bridges (20,21). Lantibiotics are produced as prepeptides encoded by structural genes. The unusual residues are created in the prepeptide C-terminal part (propeptide) by posttranslational modifications, whereas the prepeptide N-terminal leader sequence is cleaved off (4,20,21). The unusual residues are mainly the ␣,␤-unsaturated amino acids dehydroalanine (Dha) and dehydrobutyrine (Dhb) and the residues lanthionine (Lan) and 3-methyllanthionine (MeLan) harboring the thioether bonds. Dehydrations of serine and threonine produce Dha and Dhb, respectively, which are targets for nucleophilic addition of the SH group of cysteine residues, yielding Lan and MeLan. The most studied linear (type A) lantibiotics belong to class AI, which includes in particular nisin, subtilin, Pep5, and epidermin (4, 21). Biosynthesis of these lantibiotics requires two modification enzymes, LanB and LanC (Lan refers collectively to homologous proteins of different lantibiotic systems). LanB would be involved in the dehydration process and LanC in thioether bond formation, as shown in the cases of nisin and Pep5, respectively (10,14). It has been shown in the cases of nisin and subtilin that LanB and LanC form a lantibiotic synthetase complex also including the transmembrane ATP-binding cassette (ABC) transporter LanT and that both LanB and LanC interact directly with the lantibiotic prepeptide (11,22). In comparison, information related to the biosynthesis of other type A lantibiotics is scarce. Lacticin 481 contains 1 Dhb, 1 MeLan, and 2 Lan residues responsible for a rather globular C terminus, whereas the N-terminal part is unbridged (16,20,25). This lantibiotic is representative of several highly similar bacteriocins (streptococcin A-FF22, mutacin II, salivaricin A, variacin, streptococcin A-M49, and butyrivibriocin OR79A) that have been regrouped so far into class AII (9, 13). The gene clusters for lacticin 481, mutacin II, and streptococcin A-FF22 have been reported (3,13,18). They are similarly organized, each including the structural gene lanA followed by the genes lanMTFEG ( Fig. 1) but no counterp...

Maturation by LctT Is Required for Biosynthesis of Full-Length Lantibiotic Lacticin 481

“…Similar genes, collectively named lanAMTFEG, were found in the operons for lantibiotics of the lacticin 481 group (2,14,15). The functions of the lctM and lctFEG products were experimentally determined: LctM creates the unusual residues in LctA (25,27), and LctFEG constitutes an immunity system protecting the lacticin 481 producer strain against its own lantibiotic (20). The functions of the proteins encoded by lanT genes of the lacticin 481 group were deduced from their similarities to ATP-binding cassette (ABC) transporters possessing an N-terminal protease domain.…”

Characterization of ISRgn 1 , a Novel Insertion Sequence of the IS 3 Family Isolated from a Bacteriocin-Negative Mutant of Ruminococcus gnavus E1

“…It is 248 amino acids long, whereas typical LanM proteins consist of over 900 residues. Furthermore, RumN lacks the C-terminal region, which is thought to be involved in the formation of thioether bonds from previously didehydrated residues in lantibiotic prepeptides (17,21). Second, no other genes typically associated with bacteriocin production, as that encoding the specific transporter, have been found in the vicinity of rumN.…”

“…strain HIL Y-85,54728 (1). The following ORF, rumN, encoded a putative protein of 248 amino acids (29.2 kDa) exhibiting significant sequence similarity (25% identity, 43% similarity) with the N-terminal region of MrsM, the modifying enzyme of the mersacidin precursor (1), and other LanM proteins supposed to catalyze dehydration and subsequent thioether ring formation in lantibiotic prepeptides (17,21). Both rumB and rumN were named on the basis of database similarity searches and were in accordance with conventional lantibiotic clusters nomenclature (6).…”

The Expanding Role of Lipid II as a Target for Lantibiotics

“…This work has shown that in the biosynthesis of nisin, two separate enzymes carry out the dehydration (NisB) and cyclization (NisC) reactions, prior to export and leader peptide removal by translocase (NisT) and protease (NisP) enzymes. Analogous enzyme systems have also been reported for a number of other lantibiotics [56][57][58][59].…”