From nature to creation: Going around in circles, the art of peptide cyclization

An arresten-derived anti-angiogenic peptide triggers apoptotic cell death in endothelial cells

BACKGROUND

In recent years, anti-angiogenic peptides have received considerable attention as candidates for cancer treatment. Arresten is an angiogenesis inhibitor that cleaves from the α1 chain of type IV collagen and stimulates apoptosis in endothelial cells. We have recently indicated that a peptide corresponding to the amino acid 78 to 86 of arresten, so-called Ars, prevented the migration and tube formation of HUVECs and the colon carcinoma growth in mice significantly. The current study aimed to determine whether induction of apoptotic cell death in endothelial cells is one of the biochemical mechanisms of this anti-angiogenic peptide.

METHODS AND RESULTS

This hypothesis was assessed using the MTT assay, cell cycle analysis, Annexin V-FITC/PI staining, BCL2, CASP8, CASP9, p53, and CDKN2A gene expression studies as well as evaluating apoptosis in tumor tissues by TUNEL assay. Results demonstrated that 40 µM of Ars significantly stimulated 46.2% of early and late apoptosis in HUVECs compared to 13.6% in the untreated cells and did not significantly alter the cell cycle distribution. Moreover, BCL2 and CASP8 were down-regulated, while CASP9 and p53 were up-regulated in endothelial cells. CDKN2A gene expression, the regulator of G1 cell cycle arrest, was not significantly altered.

CONCLUSIONS

It might be suggested that Ars induced apoptosis in endothelial cells through the mitochondrial pathway and had no effect on the cell cycle. Besides, Ars induced apoptosis significantly in vivo. However, further studies are required to confirm the detailed molecular mechanism of Ars, this peptide has the potential to be optimized for clinical translations.

The Current and Promising Oral Delivery Methods for Protein- and Peptide-Based Drugs

Drugs based on peptides and proteins (PPs) have been widely used in medicine, beginning with insulin therapy in patients with diabetes mellitus over a century ago. Although the oral route of drug administration is the preferred one by the vast majority of patients and improves compliance, medications of this kind due to their specific chemical structure are typically delivered parenterally, which ensures optimal bioavailability. In order to overcome issues connected with oral absorption of PPs such as their instability depending on digestive enzymes and pH changes in the gastrointestinal (GI) system on the one hand, but also their limited permeability across physiological barriers (mucus and epithelium) on the other hand, scientists have been strenuously searching for novel delivery methods enabling peptide and protein drugs (PPDs) to be administered enterally. These include utilization of different nanoparticles, transport channels, substances enhancing permeation, chemical modifications, hydrogels, microneedles, microemulsion, proteolytic enzyme inhibitors, and cell-penetrating peptides, all of which are extensively discussed in this review. Furthermore, this article highlights oral PP therapeutics both previously used in therapy and currently available on the medical market.

Identification of the functional PD-L1 interface region responsible for PD-1 binding and initiation of PD-1 signaling

The PD-1/PD-L1 checkpoint pathway is important for regulating immune responses and can be targeted by immunomodulatory drugs to treat a variety of immune disorders. However, the precise protein-protein interactions required for the initiation of PD-1/PD-L1 signaling are currently unknown. Previously, we designed a series of first-generation PD-1 targeting peptides based on the native interface region of programmed death ligand 1 (PD-L1) that effectively reduced PD-1/PD-L1 binding. In this work, we further characterized the previously identified lead peptide, MN1.1, to identify key PD-1 binding residues and design an optimized peptide, MN1.4. We show MN1.4 is significantly more stable than MN1.1 in serum and retains the ability to block PD-1/PD-L1 complex formation. We further characterized the immunomodulatory effects of MN1.4 treatment by measuring markers of T cell activation in a co-culture model with ovarian cancer cells and peripheral blood mononuclear cells. We found MN1.4 treatment reduced cytokine secretion and suppressed T cell responses in a similar manner as recombinant PD-L1. Therefore, the PD-L1 interface region used to design MN1.4 appeared sufficient to initiate PD-1 signaling and likely represents the minimum necessary region of PD-L1 required for PD-1 recognition. We propose a peptide agonist for PD-1, such as MN1.4, could have several applications for treating autoimmune disorders caused by PD-1 deficiencies such as type 1 diabetes, inflammatory arthritis, or autoimmune side effects arising from monoclonal antibody-based cancer immunotherapies.

Lipidization as a tool toward peptide therapeutics

Peptides, as potential therapeutics continue to gain importance in the search for active substances for the treatment of numerous human diseases, some of which are, to this day, incurable. As potential therapeutic drugs, peptides have many favorable chemical and pharmacological properties, starting with their great diversity, through their high affinity for binding to all sort of natural receptors, and ending with the various pathways of their breakdown, which produces nothing but amino acids that are nontoxic to the body. Despite these and other advantages, however, they also have their pitfalls. One of these disadvantages is the very low stability of natural peptides. They have a short half-life and tend to be cleared from the organism very quickly. Their instability in the gastrointestinal tract, makes it impossible to administer peptidic drugs orally. To achieve the best pharmacologic effect, it is desirable to look for ways of modifying peptides that enable the use of these substances as pharmaceuticals. There are many ways to modify peptides. Herein we summarize the approaches that are currently in use, including lipidization, PEGylation, glycosylation and others, focusing on lipidization. We describe how individual types of lipidization are achieved and describe their advantages and drawbacks. Peptide modifications are performed with the goal of reaching a longer half-life, reducing immunogenicity and improving bioavailability. In the case of neuropeptides, lipidization aids their activity in the central nervous system after the peripheral administration. At the end of our review, we summarize all lipidized peptide-based drugs that are currently on the market.

Modification and Delivery of Enkephalins for Pain Modulation

Chronic pain negatively affects patient's quality of life and poses a significant economic burden. First line pharmaceutical treatment of chronic pain, including NSAIDs or antidepressants, is often inefficient to reduce pain, or produces intolerable adverse effects. In such cases, opioids are frequently prescribed for their potent analgesia, but chronic opioid use is also frequently associated with debilitating side effects that may offset analgesic benefits. Nonetheless, opioids continue to be widely utilized due to the lack of effective alternative analgesics. Since their discovery in 1975, a class of endogenous opioids called enkephalins (ENKs) have been investigated for their ability to relieve pain with significantly reduced adverse effects compared to conventional opioids. Their low metabolic stability and inability to cross biological membranes, however, make ENKs ineffective analgesics. Over past decades, much effort has been invested to overcome these limitations and develop ENK-based pain therapies. This review summarizes and describes chemical modifications and ENK delivery technologies utilizing ENK conjugates, nanoparticles and ENK gene delivery approaches and discusses valid lessons, challenges, and future directions of this evolving field.

Challenges and opportunities in delivering oral peptides and proteins

INTRODUCTION

Rapid advances in bioengineering enable the use of complex proteins as therapeutic agents to treat diseases. Compared with conventional small molecule drugs, proteins have multiple advantages, including high bioactivity and specificity with low toxicity. Developing oral dosage forms with active proteins is a route to improve patient compliance and significantly reduce production costs. However, the gastrointestinal environment remains a challenge to this delivery path due to enzymatic degradation, low permeability, and weak absorption, leading to reduced delivery efficiency and poor clinical outcomes.

AREAS COVERED

This review describes the barriers to oral delivery of peptides and complex proteins, current oral delivery strategies utilized and the opportunities and challenges ahead to try and circumvent these barriers. Oral protein drugs on the market and clinical trials provide insights and approaches for advancing delivery strategies.

EXPERT OPINION

Although most current studies on oral protein delivery rely on in vitro and in vivo animal data, the safety and limitations of the approach in humans remain uncertain. The shortage of clinical data limits the development of new or alternative strategies. Therefore, designing appropriate oral delivery strategies remains a significant challenge and requires new ideas, innovative design strategies and novel model systems.

Exploring the Limits of Cyanobactin Macrocyclase PatGmac: Cyclization of PawS-Derived Peptide Sunflower Trypsin Inhibitor-1 and Cyclotide Kalata B1

The subtilisin-like macrocyclase PatGmac is produced by the marine cyanobacterium Prochloron didemni. This enzyme is involved in the last step of the biosynthesis of patellamides, a cyanobactin type of ribosomally expressed and post-translationally modified cyclic peptides. PatGmac recognizes, cleaves, and cyclizes precursor peptides after a specific recognition motif comprised of a C-terminal tail with the sequence motif -AYDG. The result is the native macrocyclic patellamide, which has eight amino acid residues. Macrocyclase activity can be exploited by incorporating that motif in other short linear peptide precursors, which then are formed into head-to-tail cyclized peptides. Here, we explore the possibility of using PatGmac in the cyclization of peptides larger than the patellamides, namely, the PawS-derived peptide sunflower trypsin inhibitor-1 (SFTI-1) and the cyclotide kalata B1. These peptides fall under two distinct families of disulfide constrained macrocyclic plant peptides. They are both implicated as scaffolds for drug design due to their structures and unusual stability. We show that PatGmac can be used to efficiently cyclize the 14 amino acid residue long SFTI-1, but less so the 29 amino acid residue long kalata B1.

Synthetic corticotropins and the GABA-receptor system: Direct and delayed effects

The central effectors of the stress system are greatly interconnected and include, among others, a large group of peptides derived from proopiomelanocortin. In addition to natural corticotropins, a number of artificial molecules that contain some ACTH fragments in their structure are also referred to members of this family. Some of them possess a wide range of biological activity. The molecular mechanism underlying the biological activity of such peptides is partly based on allosteric modulation of various receptors. We analyzed the ability of some biologically active synthetic corticotropins (ACTH(4-7)PGP, ACTH(6-9)PGP, ACTH(7-10)PGP), and glyproline PGPL to affect the GABA-receptor system of rat brain. The effects of the peptides were studied in the isolated plasma membranes of brain cells, as well as after systemic peptide administration in the rat model of acute restraint stress. The delayed effect of stress or preadministration of each of the studied peptides on [³ H]GABA binding was different for its high- and low-affinity-specific sites. The studied peptides individually affected the binding of [³ H]GABA in their own way. Acute restraint stress caused a decrease in [³ H]GABA binding at its low-affine site and did not affected the high-affine site. Preliminary peptide administration did not influence this effect of stress.

A comprehensive review of microorganism-derived cyclic peptides: Bioactive functions and food safety applications

Cyclic peptides possess advanced structural characteristics of stability and play a vital role in medical treatment and agriculture. However, the biological functions of microorganism-derived cyclic peptides (MDCPs) and their applications in food industry were relatively absent. MDCPs are derived from extensive fermented food or soil. In this review, the synthesis approaches and structural characteristics are overviewed, while the interrelationship between bioactivities and functions is emphasized. This review summarizes the bioactivities of MDCPs from in vitro to in vivo, including antimicrobial activities, immune regulation, and antiviral cell activation. Their multiple functions as well as applications during food product processing, packaging, and storage are also comprehensively reviewed. Remarkably, some potential risks and cytotoxicity of MDCPs are also critically discussed. Moreover, future applications of MDCPs in the development of novel food additives and bioengineering materials are organized. Based on this review of native MDCPs, it is noteworthy that expected improvements of synthetic cyclic peptides in bioactive properties present potential valuable applications in future food, including artificial meat.

Engineering Approaches for the Development of Antimicrobial Peptide-Based Antibiotics

Antimicrobial peptides (AMPs) have received increasing attention as potential alternatives for future antibiotics because of the rise of multidrug-resistant (MDR) bacteria. AMPs are small cationic peptides with broad-spectrum antibiotic activities and different action mechanisms to those of traditional antibiotics. Despite the desirable advantages of developing peptide-based antimicrobial agents, the clinical applications of AMPs are still limited because of their enzymatic degradation, toxicity, and selectivity. In this review, structural modifications, such as amino acid substitution, stapling, cyclization of peptides, and hybrid AMPs with conventional antibiotics or other peptides, will be presented. Additionally, nanodelivery systems using metals or lipids to deliver AMPs will be discussed based on the structural properties and action mechanisms of AMPs.

Intramolecular covalent bonds in Gram-positive bacterial surface proteins

Gram-positive bacteria experience considerable mechanical perturbation when adhering to host surfaces during colonization and infection. They have evolved various adhesion proteins that are mechanically robust to ensure strong surface adhesion. Recently, it was discovered that these adhesion proteins contain rare, extra intramolecular covalent bonds that stabilize protein structures and participate in surface bonding. These intramolecular covalent bonds include isopeptides, thioesters, and ester bonds, which often form spontaneously without the need for additional enzymes. With the development of single-molecule force spectroscopy techniques, the detailed mechanical roles of these intramolecular covalent bonds have been revealed. In this review, we summarize the recent advances in this area of research, focusing on the link between the mechanical stability and function of these covalent bonds in Gram-positive bacterial surface proteins. We also highlight the potential impact of these discoveries on the development of novel antibiotics and chemical biology tools.

Synthesis of Cyclic Peptides in SPPS with Npb-OH Photolabile Protecting Group

Significant efforts have been made in recent years to identify more environmentally benign and safe alternatives to side-chain protection and deprotection in solid-phase peptide synthesis (SPPS). Several protecting groups have been endorsed as suitable candidates, but finding a greener protecting group in SPPS has been challenging. Here, based on the 2-(o-nitrophenyl) propan-1-ol (Npp-OH) photolabile protecting group, a structural modification was carried out to synthesize a series of derivatives. Through experimental verification, we found that 3-(o-Nitrophenyl) butan-2-ol (Npb-OH) had a high photo-release rate, high tolerance to the key conditions of Fmoc-SPPS (20% piperidine DMF alkaline solution, and pure TFA acidic solution), and applicability as a carboxyl-protective group in aliphatic and aromatic carboxyl groups. Finally, Npb-OH was successfully applied to the synthesis of head–tail cyclic peptides and side-chain–tail cyclic peptides. Moreover, we found that Npb-OH could effectively resist diketopiperazines (DKP). The α-H of Npb-OH was found to be necessary for its photosensitivity in comparison to 3-(o-Nitrophenyl)but-3-en-2-ol (Npbe-OH) during photolysis-rate verification.

Macrocyclic DNA-encoded chemical libraries: a historical perspective

While macrocyclic peptides are extensively researched for therapeutically relevant protein targets, DNA-encoded chemical libraries (DELs) are developed at a quick pace to discover novel small molecule binders. The combination of both fields has been explored since 2004 and the number of macrocyclic peptide DELs is steadily increasing. Macrocycles with high affinity and potency were identified for diverse classes of proteins, revealing DEL's huge potential. By giving a historical perspective, we would like to review the methods which permitted the rise of macrocyclic peptide DELs, describe the different DELs which were created and discuss the achievements and challenges of this emerging field.

Defensins: The natural peptide antibiotic

Defensins are a family of cationic antimicrobial peptides active against a broad range of infectious microbes including bacteria, viruses and fungi, playing important roles as innate effectors and immune modulators in immunological control of microbial infection. Their antibacterial properties and unique mechanisms of action have garnered considerable interest in developing defensins into a novel class of natural antibiotic peptides to fend off pathogenic infection by bacteria, particularly those resistant to conventional antibiotics. However, serious pharmacological and technical obstacles, some of which are unique to defensins and others are common to peptide drugs in general, have hindered the development and clinical translation of defensins as anti-infective therapeutics. To overcome them, several technologies have been developed, aiming for improved functionality, prolonged circulation time, enhanced proteolytic stability and bioavailability, and efficient and controlled delivery and release of defensins to the site of infection. Additional challenges include the alleviation of potential toxicity of defensins and their cost-effective manufacturing. In this review, we briefly introduce defensin biology, focus on various transforming strategies and practical techniques developed for defensins and their derivatives as antibacterial therapeutics, and conclude with a summation of future challenges and possible solutions.

One-Pot Cyclization and Cleavage of Peptides with N-Terminal Cysteine via the N,S-Acyl Shift of the N-2-[Thioethyl]glycine Residue

We developed a one-pot method for peptide cleavage from a solid support via the N,S-acyl shift of N-2-[thioethyl]glycine and transthioesterification using external thiols to produce cyclic peptides through native chemical self-ligation with the N-terminal cysteine. The feasibility of this methodology is validated by the syntheses of model short peptides, including a tetrapeptide, the bicyclic sunflower trypsin inhibitor SFTI-1, and rhesus Θ-defensin RTD-1. Synthesis of the whole peptide precursor can be fully automated and proceeds without epimerization or dimerization.

Oral delivery of proteins and peptides: Challenges, status quo and future perspectives

Proteins and peptides (PPs) have gradually become more attractive therapeutic molecules than small molecular drugs due to their high selectivity and efficacy, but fewer side effects. Owing to the poor stability and limited permeability through gastrointestinal (GI) tract and epithelia, the therapeutic PPs are usually administered by parenteral route. Given the big demand for oral administration in clinical use, a variety of researches focused on developing new technologies to overcome GI barriers of PPs, such as enteric coating, enzyme inhibitors, permeation enhancers, nanoparticles, as well as intestinal microdevices. Some new technologies have been developed under clinical trials and even on the market. This review summarizes the history, the physiological barriers and the overcoming approaches, current clinical and preclinical technologies, and future prospects of oral delivery of PPs.

Antimicrobial peptides towards clinical application: Delivery and formulation

Antimicrobial peptides hold promise to supplement small molecules antibiotics and combat the multidrug resistant microbes. There are however technical hurdles towards the clinical applications, largely due to the inherent limitations of peptides including stability, cytotoxicity and bioavailability. Here we review recent studies concerning the delivery and formulation of antimicrobial peptides, by categorizing the different strategies as driven by physical interactions or chemical conjugation reactions, and carriers ranging from inorganic based ones (including gold, silver and silica based solid nanoparticles) to organic ones (including micelle, liposome and hydrogel) are covered. Besides, targeted delivery of antimicrobial peptides or using antimicrobial peptides as the targeting moiety, and responsive release of the peptides after delivery are also reviewed. Lastly, strategies towards the increase of oral bioavailability, from both physical or chemical methods, are highlighted. Altogether, this article provides a comprehensive review of the recent progress of the delivery and formulation of antimicrobial peptides towards clinical application.

Fluorescent Self-Threaded Peptide Probes for Biological Imaging

A general synthetic method creates a new class of covalently connected, self-threaded, fluorescent molecular probes with figure-eight topology, an encapsulated deep-red fluorophore, and two peripheral peptide loops. The globular molecular shape and rigidified peptide loops enhance imaging performance by promoting water solubility, eliminating probe self-aggregation, and increasing probe stability. Moreover, the peptide loops determine the affinity and selectivity for targets within complex biological samples such as cell culture, tissue histology slices, or living subjects. For example, a probe with cell-penetrating peptide loops targets the surface of cell plasma membranes, whereas, a probe with bone-targeting peptide loops selectively stains the skeleton within a living mouse. The unique combination of bright deep-red fluorescence, high stability, and predictable peptide-based targeting is ideal for photon intense fluorescence microscopy and biological imaging.

Head-to-Tail Cyclization after Interaction with Trypsin: A Scorpion Venom Peptide that Resembles Plant Cyclotides

Peptidase inhibitors (PIs) have been broadly studied due to their wide therapeutic potential for human diseases. A potent trypsin inhibitor from Tityus obscurus scorpion venom was characterized and named ToPI1, with 33 amino acid residues and three disulfide bonds. The X-ray structure of the ToPI1:trypsin complex, in association with the mass spectrometry data, indicate a sequential set of events: the complex formation with the inhibitor Lys³² in the trypsin S1 pocket, the inhibitor C-terminal residue Ser³³ cleavage, and the cyclization of ToPI1 via a peptide bond between residues Ile¹ and Lys³². Kinetic and thermodynamic characterization of the complex was obtained. ToPI1 shares no sequence similarity with other PIs characterized to date and is the first PI with CS-α/β motif described from animal venoms. In its cyclic form, it shares structural similarities with plant cyclotides that also inhibit trypsin. These results bring new insights for studies with venom compounds, PIs, and drug design.

Design, synthesis, structural analysis and biochemical studies of stapled AIF(370-394) analogues as ligand of CypA

BACKGROUND

The neuronal apoptotic process requires the nuclear translocation of Apoptosis Inducing Factor (AIF) in complex with Cyclophilin A (CypA) with consequent chromatin condensation and DNA degradation events. Targeting CypA by delivering an AIF-blocking peptide (AIF(370-394)) provides a significant neuroprotection, demonstrating the biological relevance of the AIF/CypA complex. To date pharmaceutical compounds targeting this complex are missing.

METHODS

We designed and synthesized a set of mono and bicyclic AIF(370-394) analogs containing both disulfide and 1,2,3-triazole bridges, in the attempt to both stabilize the peptide conformation and improve its binding affinity to CypA. Peptide structures in solution and in complex with CypA have been studied by circular dichroism (CD), Nuclear Magnetic Resonance (NMR) and molecular modeling. The ability of stapled peptides to interact with CypA was evaluated by using Epic Corning label free technique and Isothermal Titration Calorimetry experiments.

RESULTS

We identified a stapled peptide analogue of AIF(370-394) with a ten-fold improved affinity for CypA. Molecular modeling studies reveal that the new peptide acquires β-turn/β-fold structures and shares with the parent molecule the same binding region on CypA.

CONCLUSIONS

Data obtained provide invaluable assistance in designing new ligand of CypA for therapeutic approaches in neurodegenerative diseases.

GENERAL SIGNIFICANCE

Due to the crucial role of AIF/CypA complex formation in neurodegeneration, identification of selective inhibitors is of high importance for targeted therapies. We describe new bicyclic peptide inhibitors with improved affinity for CypA, investigating the kinetic, thermodynamic and structural effects of conformational constraints on the protein-ligand interaction, and their utility for drug design.

Mapping and Exploiting the Promiscuity of OxyB toward the Biocatalytic Production of Vancomycin Aglycone Variants

Vancomycin is one of the most important clinical antibiotics in the fight against infectious disease. Its biological activity relies on three aromatic cross-links, which create a cup-shaped topology and allow tight binding to nascent peptidoglycan chains. The cytochrome P450 enzymes OxyB, OxyA, and OxyC have been shown to introduce these synthetically challenging aromatic linkages. The ability to utilize the P450 enzymes in a chemo-enzymatic scheme to generate vancomycin derivatives is appealing but requires a thorough understanding of their reactivities and mechanisms. Herein, we systematically explore the scope of OxyB biocatalysis and report installation of diverse diaryl ether and biaryl cross-links with varying macrocycle sizes and compositions, when the enzyme is presented with modified vancomycin precursor peptides. The structures of the resulting products were determined using one-dimensional/two-dimensional nuclear magnetic resonance spectroscopy, high-resolution mass spectrometry (HR-MS), tandem HR-MS, and isotopic labeling, as well as ultraviolet-visible light absorption and fluorescence emission spectroscopies. An exploration of the biological activities of these alternative OxyB products surprisingly revealed antifungal properties. Taking advantage of the promiscuity of OxyB, we chemo-enzymatically generated a vancomycin aglycone variant containing an expanded macrocycle. Mechanistic implications for OxyB and future directions for creating vancomycin analogue libraries are discussed.

Chloride-Assisted Peptide Macrocyclization

The role of the Cl^- anion as a templating agent for the synthesis of cyclopeptides was assessed through the preparation of three new homocyclolysines and other six cyclic peptides by head-to-tail lactamization. Isolated yields of products obtained by chloride-templating approach were considerably higher than those gained by a cation-promoted procedure, whereby, in some cases, only the anion-assisted synthesis yielded the desired cyclopeptides.

Simplified Head-to-Tail Cyclic Polypeptides as Biomaterial-Associated Antimicrobials with Endotoxin Neutralizing and Anti-Inflammatory Capabilities

The therapeutic application of antimicrobial peptides (AMPs), a potential type of peptide-based biomaterial, is impeded by their poor antimicrobial activity and potential cytotoxicity as a lack of understanding of their structure–activity relationships. In order to comprehensively enhance the antibacterial and clinical application potency of AMPs, a rational approach was applied to design amphiphilic peptides, including head-to-tail cyclic, linear and D-proline antimicrobial peptides using the template (IR)_nP(IR)_nP (n = 1, 2 and 3). Results showed that these amphiphilic peptides demonstrated antimicrobial activity in a size-dependent manner and that cyclic peptide OIR3, which contained three repeating units (IR)3, had greater antimicrobial potency and cell selectivity than liner peptide IR3, DIR3 with D-Pro and gramicidin S (GS). Surface plasmon resonance and endotoxin neutralization assays indicated that OIR3 had significant endotoxin neutralization capabilities, which suggested that the effects of OIR3 were mediated by binding to lipopolysaccharides (LPS). Using fluorescence spectrometry and electron microscopy, we found that OIR3 strongly promoted membrane disruption and thereby induced cell lysis. In addition, an LPS-induced inflammation assay showed that OIR3 inhibited the pro-inflammatory factor TNF-α in RAW264.7 cells. OIR3 was able to reduce oxazolone-induced skin inflammation in allergic dermatitis mouse model via the inhibition of TNF-α, IL-1β and IL-6 mRNA expression. Collectively, the engineered head-to-tail cyclic peptide OIR3 was considerable potential candidate for use as a clinical therapeutic for the treatment of bacterial infections and skin inflammation.

Novel Cyclic Biphalin Analogues by Ruthenium-Catalyzed Ring Closing Metathesis: in Vivo and in Vitro Biological Profile

In this work we report the application of the ring-closing metathesis (RCM) to the preparation of two cyclic olefin-bridged analogues of biphalin (Tyr-d-Ala-Gly-Phe-NH-NH ← Phe ← Gly ← d-Ala ← Tyr), using the second generation Grubbs' catalyst. The resulting cis- and trans-cyclic isomers were identified, fully characterized, and tested in vitro at μ (ΜΟR), δ (DOR), and κ (KOR) opioid receptors and in vivo for antinociceptive activity. Both were shown to be full agonists at MOR and potential partial antagonists at DOR, with low potency KOR agonism. They also share a strong antinociceptive effect after intracerebroventricular (i.c.v.) and intravenous (i.v.) administration, higher than that of the cyclic biphalin analogues containing a disulfide bridge between the side chains of two d-Cys or d-Pen residues, previously described by our group.

Investigation of Substrate Recognition and Biosynthesis in Class IV Lanthipeptide Systems

Lanthipeptides belong to the family of ribosomally synthesized and post-translationally modified peptides (RiPPs) and are subdivided into four classes. The first two classes have been heavily studied, but less is known about classes III and IV. The lanthipeptide synthetases of classes III and IV share a similar organization of protein domains: A lyase domain at the N-terminus, a central kinase domain, and a C-terminal cyclase domain. Here, we provide deeper insight into class IV enzymes (LanLs). A series of putative producer strains was screened to identify production conditions of four new venezuelin-like lanthipeptides, and an Escherichia coli based heterologous production system was established for a fifth. The latter not only allowed production of fully modified core peptide but was also employed as the basis for mutational analysis of the precursor peptide to identify regions important for enzyme recognition. These experiments were complemented by in vitro binding studies aimed at identifying the region of the leader peptide recognized by the LanL enzymes as well as determining which domain of the enzyme is recognizing the substrate peptide. Combined, these studies revealed that the kinase domain is mediating the interaction with the precursor peptide and that a putatively α-helical stretch of residues at the center to N-terminal region of the leader peptide is important for enzyme recognition. In addition, a combination of in vitro assays and tandem mass spectrometry was used to elucidate the order of dehydration events in these systems.