Agonists of galanin subtype 2 receptor may prevent pancreatic cancer and agonists of angiotensin II type 2 receptor may prevent colorectal cancer.

Pancreatic ductal adenocarcinoma (PDAC) remains a dreadful disease with poor prognosis. While the prognosis of colorectal carcinoma (CRC) is better than that of PDAC, it still is the second-leading cause of cancer deaths worldwide. Recently, a (methyl)lanthionine-stabilized, highly receptor-specific agonist of galanin subtype 2 (GAL2) receptor inhibited the growth of GAL2 receptor-expressing patient-derived xenografts (PDX) of pancreatic cancer. Furthermore, a lanthionine-constrained agonist of angiotensin II type 2 (AT2) receptor inhibited PDX of colorectal cancer in mice. Stimulation of GAL2 receptor may modulate immune surveillance and inhibits PDAC via cell cycle inhibition and apoptosis. Consistent with GAL2 receptor-mediated tumor inhibition, for PDAC, survival is much higher for patients with high GAL2 receptor expression. Importantly, a (methyl)lanthionine-stabilized GAL2 receptor-specific agonist enhances expression of GAL2 receptor, not only in PDAC-PDX but also in healthy tissue indicating therapeutic and preventive potentials for GAL2 receptor agonists. AT2 receptor is interacting with four tumor suppressor proteins, Src homology phosphatase 1, Src homology phosphatase 2, Promyelocytic Leukemia Zinc Finger protein and Microtuble-Associated Scaffold Protein1, the latter also known as Angiotensin-II type 2 receptor-Interacting Protein. Pathways linked to these tumor suppressor proteins may enhance immune surveillance, prevent carcinogenesis, counter proliferation and stimulate apoptosis. Taken together, current data are prompting the hypothesis of a prophylactic treatment option with stable, specific and safe agonists of GAL2 receptor and AT2 receptor to prevent the emergence of pancreatic and colorectal cancer in individuals at risk.

Evolving views on the first two ligands of the angiotensin II type 2 receptor. From putative antagonists to potential agonists?

The renin-angiotensin system is one of the most complex regulatory systems that controls multiple organ functions. One of its key components, angiotensin II (Ang II), stimulates two G-protein coupled class A receptors: the Ang II type 1 (AT1) receptor and the Ang II type 2 (AT2) receptor. While stimulation of the AT1 receptor causes G-protein-dependent signaling and arrestin recruitment, the AT2 receptor seems to have a constitutively active-like conformation and appears to act via G-protein-dependent and -independent pathways. Overstimulation of the AT1 receptor may lead to unwanted effects like inflammation and fibrosis. In contrast, stimulation of the AT2 receptor leads to opposite effects thus restoring the balance. However, the role of the AT2 receptor has become controversial due to beneficial effects of putative AT2 receptor antagonists. The two first synthetic AT2 receptor-selective ligands, peptide CGP42112 and small molecule PD123319, were initially both considered antagonists. CGP42112 was subsequently considered a partial agonist and it was recently demonstrated to be a full agonist. Based on the search-term PD123319 in Pubmed, 1652 studies have investigated putative AT2 receptor antagonist PD123319. Here, we put forward literature that shows beneficial effects of PD123319 alone, even at doses too low for antagonist efficacy. These beneficial effects appear compatible with agonist-like activity via the AT2 receptor. Taken together, a more consistent image of a therapeutic role of stimulated AT2 receptor emerges which may clarify current controversies.

AT2 receptor agonist LP2 restores respiratory function in a rat model of bleomycin-induced lung remodelling.

This study aimed to evaluate the prophylactic and therapeutic potential of angiotensin II type 2 receptor peptide agonist LP2 in bleomycin-induced airway and cardiac remodeling in rats. Male Wistar rats were intratracheally instillated with bleomycin. Animals of a prophylactic arm received LP2 from day 0 at intraperitoneal doses of 1, 3 or 10 µg/kg/d, whereas animals from a therapeutic arm received this LP2 treatment from day 7. On day 28 direct lung mechanics were determined and cardiac and lung tissues were collected and (histo)morphologically assessed. Prophylactic LP2 at 1 µg/kg/d with bleomycin, versus bleomycin alone, significantly improved the airway pressure responses at fixed inflation of 4 ml (p < 0.05) and 7 ml volume (p < 0.05), static compliance (p < 0.01), inspiratory capacity (p < 0.05), lung tolerance of increased volume (p < 0.0001), right to left ventricular hypertrophy (p < 0.05). Therapeutic regime showed a similar trend as the prophylactic arm but was less effective, mostly lacking significance. However, and importantly, therapeutic LP2 at 1 µg/kg/d significantly decreased mRNA expression of collagen 1A1 (p < 0.01), of Connective Tissue Growth Factor 1 (p < 0.05) and of Tissue MetalloPeptidase inhibitor 1 (p < 0.05). In conclusion, a very low dose of 1 µg/kg/d LP2 has capacity to counter bleomycin-induced impairment of lung functioning and consequent cardiac remodeling.

Galanin 2 Receptor: A Novel Target for a Subset of Pancreatic Ductal Adenocarcinoma.

Galanin is a 30 amino acid peptide that stimulates three subtype receptors (GAL1-3R). M89b is a lanthionine-stabilized, C-terminally truncated galanin analog that specifically stimulates GAL2R. We investigated the potential of M89b as a therapeutic for pancreatic ductal adenocarcinoma (PDAC) and assessed its safety. The anti-tumor activity of subcutaneously injected M89b on the growth of patient-derived xenografts of PDAC (PDAC-PDX) in mice was investigated. In addition, the safety of M89b was assessed in vitro using a multi-target panel to measure the off-target binding and modulation of enzyme activities. In a PDAC-PDX with a high GAL2R expression, M89b completely inhibited the growth of the tumor (p < 0.001), while in two PDAC-PDXs with low GAL2R expression, low or negligeable inhibition of tumor growth was measured, and in the PDX without GAL2R expression no influence on the tumor growth was observed. The M89b treatment of the GAL2R high-PDAC-PDX-bearing mice led to a reduction in the expression of RacGap1 (p < 0.05), PCNA (p < 0.01), and MMP13 (p < 0.05). In vitro studies involving a multi-target panel of pharmacologically relevant targets revealedexcellent safety of M89b. Our data indicated that GAL2R is a safe and valuable target for treating PDACs with high GAL2R expression.

Intranasal Delivery of a Methyllanthionine-Stabilized Galanin Receptor-2-Selective Agonist Reduces Acute Food Intake.

The regulatory (neuro)peptide galanin is widely distributed in the central and peripheral nervous systems, where it mediates its effects via three G protein-coupled receptors (GAL1-3R). Galanin has a vast diversity of biological functions, including modulation of feeding behavior. However, the clinical application of natural galanin is not practicable due to its rapid in vivo breakdown by peptidases and lack of receptor subtype specificity. Much effort has been put into the development of receptor-selective agonists and antagonists, and while receptor selectivity has been attained to some degree, most ligands show overlapping affinity. Therefore, we aimed to develop a novel ligand with specificity to a single galanin receptor subtype and increased stability. To achieve this, a lanthionine amino acid was enzymatically introduced into a galanin-related peptide. The residue's subsequent cyclization created a conformational constraint which increased the peptide's receptor specificity and proteolytic resistance. Further exchange of certain other amino acids resulted in a novel methyllanthionine-stabilized galanin receptor agonist, a G1pE-T3N-S6A-G12A-methyllanthionine[13-16]-galanin-(1-17) variant, termed M89b. M89b has exclusive specificity for GAL2R and a prolonged half-life in serum. Intranasal application of M89b to unfasted rats significantly reduced acute 24 h food intake inducing a drop in body weight. Combined administration of M89b and M871, a selective GAL2R antagonist, abolished the anorexigenic effect of M89b, indicating that the effect of M89b on food intake is indeed mediated by GAL2R. This is the first demonstration of in vivo activity of an intranasally administered lanthipeptide. Consequently, M89b is a promising candidate for clinical application as a galanin-related peptide-based therapeutic.

LP2, the first lanthipeptide GPCR agonist in a human pharmacokinetics and safety study.

Introduction of a lanthionine into a peptide may enhance target affinity, target specificity and proteolytic resistance. This manuscript reports preclinical safety studies and the first-in-human study with the lanthipeptide AT2R agonist LP2, a structural analog of cAng-(1-7), whose N-terminus was protected against aminopeptidases by the presence of a d-lysine. None of the preclinical studies, including an in vitro multitarget panel, behavioral, respiratory and cardiovascular measurements, genotoxicity and toxicity studies in rat and dog, posed any safety concern. Due to lack of toxicity the maximum tolerated dose was not reached neither in rat nor in dog. In the human dose escalation study, healthy male volunteers received a single 1 mL subcutaneous injection (0.001 mg, 0.01 mg or 0.1 mg) of LP2 or matching placebo. In contrast to angiotensin II which has a T1/2 in plasma of < 1 min, LP2 has a T1/2 of approximately 2.1-2.6 hours. The fraction of the dose excreted unchanged in urine ranged from 84.73 ± 10.4 % at a dose of 0.001 mg to 66.4 ± 3.9 % at 0.1 mg. There were no deaths, serious adverse events or subject withdrawals as a result of an adverse event. The incidence of adverse events was 16.7 %; each was mild in severity. One adverse event, peripheral coldness, was considered to be possibly related to LP2 at 0.001 mg LP2. None of the results was considered to pose a clinically relevant safety concern. This study supports the potential for the therapeutic use of lanthipeptides.

Biosynthesis of lanthionine-constrained agonists of G protein-coupled receptors.

The conformation with which natural agonistic peptides interact with G protein-coupled receptor(s) (GPCR(s)) partly results from intramolecular interactions such as hydrogen bridges or is induced by ligand-receptor interactions. The conformational freedom of a peptide can be constrained by intramolecular cross-links. Conformational constraints enhance the receptor specificity, may lead to biased activity and confer proteolytic resistance to peptidic GPCR agonists. Chemical synthesis allows to introduce a variety of cross-links into a peptide and is suitable for bulk production of relatively simple lead peptides. Lanthionines are thioether bridged alanines of which the two alanines can be introduced at different distances in chosen positions in a peptide. Thioether bridges are much more stable than disulfide bridges. Biosynthesis of lanthionine-constrained peptides exploiting engineered Gram-positive or Gram-negative bacteria that contain lanthionine-introducing enzymes constitutes a convenient method for discovery of lanthionine-stabilized GPCR agonists. The presence of an N-terminal leader peptide enables dehydratases to dehydrate serines and threonines in the peptide of interest after which a cyclase can couple the formed dehydroamino acids to cysteines forming (methyl)lanthionines. The leader peptide also guides the export of the formed lanthionine-containing precursor peptide out of Gram-positive bacteria via a lanthipeptide transporter. An engineered cleavage site in the C-terminus of the leader peptide allows to cleave off the leader peptide yielding the modified peptide of interest. Lanthipeptide GPCR agonists are an emerging class of therapeutics of which a few examples have demonstrated high efficacy in animal models of a variety of diseases. One lanthipeptide GPCR agonist has successfully passed clinical Phase Ia.

Does activation of the protective Renin-Angiotensin System have therapeutic potential in COVID-19?

Infection of lung cells by the corona virus results in a loss of the balance between, on the one hand, angiotensin II-mediated stimulation of the angiotensin II type 1 receptor and, on the other hand, stimulation of the angiotensin II type 2 receptor and/or the Mas receptor. The unbalanced enhanced stimulation of the angiotensin II type 1 receptor causes inflammation, edema and contributes to the pathogenesis of severe acute respiratory distress syndrome. Here we hypothesize that stable, receptor-specific agonists of the angiotensin II type 2 receptor and of the Mas receptor are molecular medicines to treat COVID-19 patients. These agonists have therapeutic potential in the acute disease but in addition may reduce COVID-19-associated long-term pulmonary dysfunction and overall end-organ damage of this disease.

High-Throughput Screening for Substrate Specificity-Adapted Mutants of the Nisin Dehydratase NisB.

Microbial lanthipeptides are formed by a two-step enzymatic introduction of (methyl)lanthionine rings. A dehydratase catalyzes the dehydration of serine and threonine residues, yielding dehydroalanine and dehydrobutyrine, respectively. Cyclase-catalyzed coupling of the formed dehydroresidues to cysteines forms (methyl)lanthionine rings in a peptide. Lanthipeptide biosynthetic systems allow discovery of target-specific, lanthionine-stabilized therapeutic peptides. However, the substrate specificity of existing modification enzymes impose limitations on installing lanthionines in non-natural substrates. The goal of the present study was to obtain a lanthipeptide dehydratase with the capacity to dehydrate substrates that are unsuitable for the nisin dehydratase NisB. We report high-throughput screening for tailored specificity of intracellular, genetically encoded NisB dehydratases. The principle is based on the screening of bacterially displayed lanthionine-constrained streptavidin ligands, which have a much higher affinity for streptavidin than linear ligands. The designed NisC-cyclizable high-affinity ligands can be formed via mutant NisB-catalyzed dehydration but less effectively via wild-type NisB activity. In Lactococcus lactis, a cell surface display precursor was designed comprising DSHPQFC. The Asp residue preceding the serine in this sequence disfavors its dehydration by wild-type NisB. The cell surface display vector was coexpressed with a mutant NisB library and NisTC. Subsequently, mutant NisB-containing bacteria that display cyclized strep ligands on the cell surface were selected via panning rounds with streptavidin-coupled magnetic beads. In this way, a NisB variant with a tailored capacity of dehydration was obtained, which was further evaluated with respect to its capacity to dehydrate nisin mutants. These results demonstrate a powerful method for selecting lanthipeptide modification enzymes with adapted substrate specificity.

An Engineered Double Lipid II Binding Motifs-Containing Lantibiotic Displays Potent and Selective Antimicrobial Activity against Enterococcus faecium.

Lipid II is an essential precursor for bacterial cell wall biosynthesis and thereby an important target for various antibiotics. Several lanthionine-containing peptide antibiotics target lipid II with lanthionine-stabilized lipid II binding motifs. Here, we used the biosynthesis system of the lantibiotic nisin to synthesize a two-lipid II binding motifs-containing lantibiotic, termed TL19, which contains the N-terminal lipid II binding motif of nisin and the distinct C-terminal lipid II binding motif of one peptide of the two-component haloduracin (i.e., HalA1). Further characterization demonstrated that (i) TL19 exerts 64-fold stronger antimicrobial activity against Enterococcus faecium than nisin(1-22), which has only one lipid II binding site, and (ii) both the N- and C-terminal domains are essential for the potent antimicrobial activity of TL19, as evidenced by mutagenesis of each single and the double domains. These results show the feasibility of a new approach to synthesize potent lantibiotics with two different lipid II binding motifs to treat specific antibiotic-resistant pathogens.

Cyclic angiotensin-(1-7) contributes to rehabilitation of animal performance in a rat model of cerebral stroke.

Peptidase-resistant, lanthionine-stabilized angiotensin-(1-7), termed cAng-(1-7), has shown therapeutic efficacy in animal models of cardiovascular, metabolic, kidney and pulmonary disease. Goal of the present study was testing the capacity of subcutaneously administered cAng-(1-7) to induce rehabilitation of animal performance in the transient middle cerebral artery occlusion rat model of cerebral stroke. 24 h after ischemic stroke induction, cAng-(1-7) was administered for 28 days at a dose of 500 µg/kg/day, either daily via subcutaneous injection or continuously via an alzet pump. Both ways of administration of cAng-(1-7) were equally effective. Measurements were continued until day 50. Compared to vehicle, cAng-(1-7) clearly demonstrated significantly increased capillary density (p < 0.01) in the affected hemisphere and improved motor and somatosensory functioning. The modified neurological severity score (p < 0.001 at days 15 and 50), stepping test (p < 0.001 at days 36-50), forelimb placement test (p < 0.001 at day 50), body swing test (p < 0.001 at days 43 and 50) all demonstrated that cAng-(1-7) caused significantly improved animal performance. Taken together the data convincingly indicate rehabilitating capacity of subcutaneously injected cAng-(1-7) in cerebral ischemic stroke.

Genetically Encoded Libraries of Constrained Peptides.

Many therapeutic peptides can still be improved with respect to target specificity, target affinity, resistance to peptidases/proteases, physical stability, and capacity to pass through membranes required for oral delivery. Several modifications can improve the peptides' properties, in particular those that impose (a) conformational constraint(s). Screening of constrained peptides and the identification of hits is greatly facilitated by the generation of genetically encoded libraries. Recent breakthrough bacterial, phage, and yeast display screening systems of ribosomally synthesized post-translationally constrained peptides, particularly those of lanthipeptides, are earning special attention. Here we provide an overview of display systems for constrained, genetically encoded peptides and indicate prospects of constrained peptide-displaying phage and bacterial systems as such in vivo.

Efficacy of lanthionine-stabilized angiotensin-(1-7) in type I and type II diabetes mouse models.

Native angiotensin-(1-7) exerts many therapeutic effects. However, it is rapidly degraded by ACE and other peptidases. This drawback is largely eliminated for lanthionine-stabilized angiotensin-(1-7), termed cAng-(1-7), which is fully resistant to ACE and has strongly increased resistance to other peptidases. Goal of the present study was to test whether cAng-(1-7) has therapeutic activity in diabetes mouse models: in a multiple low dose streptozotocin-induced model of type I diabetes and / or in a db/db model of type II diabetes. In the type I diabetes model cAng-(1-7) caused in an increase in the insulin level of 133% in week 4 (p < 0.001) compared to vehicle, and in the type II diabetes model an increase of 55% of the insulin level in week 8 (p < 0.05) compared to vehicle. cAng-(1-7) reduced blood glucose levels in the type I model by 37% at day 22 (p < 0.001) and in the type II diabetes model by 17% at day 63 of treatment (p < 0.001) and in an oral glucose tolerance test in a type II diabetes model, by 17% at week 4 (p < 0.01). cAng-(1-7) also caused a reduction of glycated hemoglobin levels in the type II diabetes model of 21% in week 6 (p < 0,001). These data are consistent with therapeutic potential of cAng-(1-7) in type I and II diabetes.

Phage display and selection of lanthipeptides on the carboxy-terminus of the gene-3 minor coat protein.

Ribosomally synthesized and post-translationally modified peptides (RiPPs) are an emerging class of natural products with drug-like properties. To fully exploit the potential of RiPPs as peptide drug candidates, tools for their systematic engineering are required. Here we report the engineering of lanthipeptides, a subclass of RiPPs characterized by multiple thioether cycles that are enzymatically introduced in a regio- and stereospecific manner, by phage display. This was achieved by heterologous co-expression of linear lanthipeptide precursors fused to the widely neglected C-terminus of the bacteriophage M13 minor coat protein pIII, rather than the conventionally used N-terminus, along with the modifying enzymes from distantly related bacteria. We observe that C-terminal precursor peptide fusions to pIII are enzymatically modified in the cytoplasm of the producing cell and subsequently displayed as mature cyclic peptides on the phage surface. Biopanning of large C-terminal display libraries readily identifies artificial lanthipeptide ligands specific to urokinase plasminogen activator (uPA) and streptavidin.

Semi-microbiological synthesis of an active lysinoalanine-bridged analog of glucagon-like-peptide-1.

Some modified glucagon-like-peptide-1 (GLP-1) analogs are highly important for treating type 2 diabetes. Here we investigated whether GLP-1 analogs expressed in Lactococcus lactis could be substrates for modification and export by the nisin dehydratase and transporter enzyme. Subsequently we introduced a lysinoalanine by coupling a formed dehydroalanine with a lysine and investigated the structure and activity of the formed lysinoalanine-bridged GLP-1 analog. Our data show: (i) GLP-1 fused to the nisin leader peptide is very well exported via the nisin transporter NisT, (ii) production of leader-GLP-1 via NisT is higher than via the SEC system, (iii) leader-GLP-1 exported via NisT was more efficiently dehydrated by the nisin dehydratase NisB than when exported via the SEC system, (iv) individual serines and threonines in GLP-1 are dehydrated by NisB to a significantly different extent, (v) an introduced Ser30 is well dehydrated and can be coupled to Lys34 to form a lysinoalanine-bridged GLP-1 analog, (vi) a lysinoalanine(30-34) variant's conformation shifts in the presence of 25% trifluoroethanol towards a higher alpha helix content than observed for wild type GLP-1 under identical condition, (vii) a lysinoalanine(30-34) GLP-1 variant has retained significant activity. Taken together the data extend knowledge on the substrate specificities of NisT and NisB and their combined activity relative to export via the Sec system, and demonstrate that introducing a lysinoalanine bridge is an option for modifying therapeutic peptides.

Mutagenesis of nisin's leader peptide proline strongly modulates export of precursor nisin.

The lantibiotic nisin is produced by Lactococcus lactis as a precursor peptide comprising a 23 amino acid leader peptide and a 34 amino acid post-translationally modifiable core peptide. We previously demonstrated that the conserved FNLD part of the leader is essential for intracellular enzyme-catalyzed introduction of lanthionines in the core peptide and also for transporter-mediated export, whereas other positions are subject to large mutational freedom. We here demonstrate that, in the absence of the extracellular leader peptidase, NisP, export of precursor nisin via the modification and transporter enzymes, NisBTC, is strongly affected by multiple substitutions of the leader residue at position -2, but not by substitution of positions in the vicinity of this site. Export levels of precursor nisin increased by more than 70% for position -2 mutants Asp, Thr, Ser, Trp, Lys, Val and decreased more than 70% for Cys, His, Met. In a strain with leader peptidase, the Pro-2Lys and Pro-2Asp precursor nisins were less efficiently cleaved by NisP than wild type precursor nisin. Taken together, the wild type precursor nisin with a proline at position -2 allows balanced export and cleavage efficiencies by precursor nisin's transporter and leader peptidase.

Discovery, Production and Modification of Five Novel Lantibiotics Using the Promiscuous Nisin Modification Machinery.

To find the right conditions to isolate natively expressed antimicrobial peptides from a wide range of different microorganisms can be a challenge. Here, we exploited a heterologous expression system to produce and characterize several novel lantibiotics. We identified 54 novel putative class I and class II lantibiotics after inspecting all publicly available prokaryotic genomes using the in-house developed mining tool BAGEL3. The genes encoding these new lantibiotics fused to the nisin leader peptide gene sequence were synthesized, and the constructs were plugged into the nisin expression and modification system. Using this approach 30 peptides could be expressed, 27 of which were dehydrated by NisBC on at least 1 predicted position. Good antimicrobial activity against several pathogenic bacteria could be demonstrated for 5 novel heterologously modified lantibiotics. Lantibiotics from Corynebacterium lipophiloflavum DSM 44291 and Streptococcus agalactiae ATCC 13813, named flavucin and agalacticin, respectively, were fully modified and displayed high antimicrobial activity. The efficiency of functional expression was significantly enhanced when we made use of the native nisin leader cleavage site, instead of an artificial factor Xa site. Thus, we describe an efficient way for heterologous production of active lantibiotics, facilitating a rapid identification of promising molecules.

Identification of essential amino acid residues in the nisin dehydratase NisB.

Nisin is a posttranslationally-modified antimicrobial peptide that has the ability to induce its own biosynthesis. Serines and threonines in the modifiable core peptide part of precursor nisin are dehydrated to dehydroalanines and dehydrobutyrines by the dehydratase NisB, and subsequently cysteines are coupled to the dehydroamino acids by the cyclase NisC. In this study, we applied extensive site-directed mutagenesis, together with direct binding studies, to investigate the molecular mechanism of the dehydratase NisB. We use a natural nisin-producing strain as a host to probe mutant-NisB functionality. Importantly, we are able to differentiate between intracellular and secreted fully dehydrated precursor nisin, enabling investigation of the NisB properties needed for the release of dehydrated precursor nisin to its devoted secretion system NisT. We report that single amino acid substitutions of conserved residues, i.e., R83A, R83M, and R87A result in incomplete dehydration of precursor nisin and prevention of secretion. Single point NisB mutants Y80F and H961A, result in a complete lack of dehydration of precursor nisin, but do not abrogate precursor nisin binding. The data indicate that residues Y80 and H961 are directly involved in catalysis, fitting well with their position in the recently published 3D-structure of NisB. We confirm, by in vivo studies, results that were previously obtained from in vitro experiments and NisB structure elucidation and show that previous findings translate well to effects seen in the original production host.

Identification of distinct nisin leader peptide regions that determine interactions with the modification enzymes NisB and NisC.

Nisin is the most prominent and applied bacteriocin that serves as a model for class I lantibiotics. The nisin leader peptide importantly determines interactions between precursor nisin and its modification enzymes NisB and NisC that mature nisin posttranslationally. NisB dehydrates serines and threonines, while NisC catalyzes the subsequent coupling of the formed dehydroamino acids to form lanthionines. Currently, little is known about how the nisin leader interacts with NisB and even less is known about its interactions with NisC. To investigate the nisin leader peptide requirements for functional interaction with the modification enzymes NisB and NisC, we systematically replaced six regions, of 2-4 amino acids each, with all-alanine regions. By performing NisB and NisC co-purification studies with these mutant leader peptides, we demonstrate that the nisin leader regions STKD(-22-19), FNLD(-18-15) and PR(-2-1) importantly contribute to the interactions of precursor nisin with both NisB and NisC, whereas the nisin leader region LVSV(-14-11) additionally contributes to the interaction of precursor nisin with NisC.

Mechanistic aspects of lanthipeptide leaders.

Lanthipeptides are ribosomally synthesized and posttranslationally modified peptides produced by microorganisms. The name lanthipeptide is derived from lanthionine, a thioether-bridged amino acid installed by dedicated modification enzymes. Serines and threonines are dehydrated and subsequently coupled to cysteines, thus forming intramolecular lanthionine rings. A well-known subclass of lanthipeptides are lantibiotics: lanthipeptides with antimicrobial activity. The lantibiotic nisin is applied worldwide in the food industry to prevent food spoilage. This review focuses on lanthipeptide leader peptides, which have a crucial and central role in lanthipeptide biosynthesis. Lanthipeptide leader peptides are present at the N-terminus within precursor lanthipeptides. Intriguingly, a single leader peptide can interact with highly different modifying enzyme(s) (domains) and furthermore induce export out of the cell via a dedicated export protein. Eventually the leader peptide is cleaved off by a leader peptidase, either extracellularly or intracellularly as part of the transporter. Recent exciting mechanistic and engineering studies ignited the unraveling of the fascinating interactions of lanthipeptide leader peptides with the lanthipeptide modification enzymes and transporters. The biosynthesis of at least some lanthipeptides is performed by a highly flexible enzyme system. Novel lantibiotics can be synthesized by fusing lanthipeptide leader peptides to completely different silent lantibiotics obtained by genome mining. Moreover, the fusion of leader peptides to the N-terminus of medically and economically important therapeutic peptides has resulted in lanthioninestabilized therapeutics with enhanced bioavailability and optimized receptor interaction.