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Species that are currently listed under the genus Brevibacillus (formerly, Bacillus brevis cluster) have been a rich source of antimicrobial peptides for many decades. The first known peptide antibiotic, gramicidin, is presumed to be produced by a Brevibacillus sp. Members of the genus are widely spread in nature. They can be found in a variety of environments including intestinal tracts of animals, seawater, and soil. Some Brevibacillus strains have been used commercially as probiotics. Bioactive peptides produced by Brevibacillus spp. include antibacterial, antifungal and anti-invertebrate agents. Brevibacillus antimicrobial peptides are synthesized through ribosomal or nonribosomal pathway; these two groups can be further categorized based on specific structural features such as cyclization and presence of lipid chain. Some of the antimicrobial compounds produced by this genus share structural similarities that were overlooked previously. For example, the structural similarity between BT peptide, brevibacillin, and bogorol was revealed only recently. Here we review and classify Brevibacillus antimicrobial peptides and summarize their bioactivities and potential applications.

Antimicrobial peptides (AMPs) are regarded as a new generation of antibiotics. Besides antimicrobial activity, AMPs also have antibiofilm, immune-regulatory, and other activities. Exploring the mechanism of action of AMPs may help in the modification and development of AMPs. Many studies were conducted on the mechanism of AMPs. The present review mainly summarizes the research status on the antimicrobial, anti-inflammatory, and antibiofilm properties of AMPs. This study not only describes the mechanism of cell wall action and membrane-targeting action but also includes the transmembrane mechanism of intracellular action and intracellular action targets. It also discusses the dual mechanism of action reported by a large number of investigations. Antibiofilm and anti-inflammatory mechanisms were described based on the formation of biofilms and inflammation. This study aims to provide a comprehensive review of the multiple activities and coordination of AMPs in vivo, and to fully understand AMPs to realize their therapeutic prospect.

In Drosophila melanogaster, recognition of an invading pathogen activates the Toll or Imd signaling pathway, triggering robust upregulation of innate immune effectors. Although the mechanisms of pathogen recognition and signaling are now well understood, the functions of the immune-induced transcriptome and proteome remain much less well characterized. Through bioinformatic analysis of effector gene sequences, we have defined a family of twelve genes - the Bomanins (Boms) - that are specifically induced by Toll and that encode small, secreted peptides of unknown biochemical activity. Using targeted genome engineering, we have deleted ten of the twelve Bom genes. Remarkably, inactivating these ten genes decreases survival upon microbial infection to the same extent, and with the same specificity, as does eliminating Toll pathway function. Toll signaling, however, appears unaffected. Assaying bacterial load post-infection in wild-type and mutant flies, we provide evidence that the Boms are required for resistance to, rather than tolerance of, infection. In addition, by generating and assaying a deletion of a smaller subset of the Bom genes, we find that there is overlap in Bom activity toward particular pathogens. Together, these studies deepen our understanding of Toll-mediated immunity and provide a new in vivo model for exploration of the innate immune effector repertoire.

In the last 20 years, an increasing number of studies have been reported on membrane active peptides. These peptides exert their biological activity by interacting with the cell membrane, either to disrupt it and lead to cell lysis or to translocate through it to deliver cargos into the cell and reach their target. Membrane active peptides are attractive alternatives to currently used pharmaceuticals and the number of antimicrobial peptides (AMPs) and peptides designed for drug and gene delivery in the drug pipeline is increasing. Here, we focus on two most prominent classes of membrane active peptides; AMPs and cell-penetrating peptides (CPPs). Antimicrobial peptides are a group of membrane active peptides that disrupt the membrane integrity or inhibit the cellular functions of bacteria, virus, and fungi. Cell penetrating peptides are another group of membrane active peptides that mainly function as cargo-carriers even though they may also show antimicrobial activity. Biophysical techniques shed light on peptide–membrane interactions at higher resolution due to the advances in optics, image processing, and computational resources. Structural investigation of membrane active peptides in the presence of the membrane provides important clues on the effect of the membrane environment on peptide conformations. Live imaging techniques allow examination of peptide action at a single cell or single molecule level. In addition to these experimental biophysical techniques, molecular dynamics simulations provide clues on the peptide–lipid interactions and dynamics of the cell entry process at atomic detail. In this review, we summarize the recent advances in experimental and computational investigation of membrane active peptides with particular emphasis on two amphipathic membrane active peptides, the AMP melittin and the CPP pVEC.

For decades, antigen presentation on major histocompatibility complex class I for T cell-mediated immunity has been considered the primary function of proteasome-derived peptides 1 , 2 . However, whether the products of proteasomal degradation play additional parts in mounting immune responses remains unknown. Antimicrobial peptides serve as a first line of defence against invading pathogens before the adaptive immune system responds. Although the protective function of antimicrobial peptides across numerous tissues is well established, the cellular mechanisms underlying their generation are not fully understood. Here we uncover a role for proteasomes in the constitutive and bacterial-induced generation of defence peptides that impede bacterial growth both in vitro and in vivo by disrupting bacterial membranes. In silico prediction of proteome-wide proteasomal cleavage identified hundreds of thousands of potential proteasome-derived defence peptides with cationic properties that may be generated en route to degradation to act as a first line of defence. Furthermore, bacterial infection induces changes in proteasome composition and function, including PSME3 recruitment and increased tryptic-like cleavage, enhancing antimicrobial activity. Beyond providing mechanistic insights into the role of proteasomes in cell-autonomous innate immunity, our study suggests that proteasome-cleaved peptides may have previously overlooked functions downstream of degradation. From a translational standpoint, identifying proteasome-derived defence peptides could provide an untapped source of natural antibiotics for biotechnological applications and therapeutic interventions in infectious diseases and immunocompromised conditions. Proteasomal degradation of cellular proteins generate defence peptides constitutively and in response to bacterial infection. Such peptides might provide a source of natural antibiotics that could lead to biotechnology applications and therapeutic interventions.

Peptide hormones, a class of pharmacologically active molecules, have a critical role in regulating energy homeostasis. Prohormone convertase 1/3 (also known as PCSK1/3) represents a key enzymatic mechanism in peptide processing, as exemplified with the therapeutic target glucagon-like peptide 1 (GLP-1) 1 , 2 . However, the full spectrum of peptides generated by PCSK1 and their functional roles remain largely unknown. Here we use computational drug discovery to systematically map more than 2,600 previously uncharacterized human proteolytic peptide fragments cleaved by prohormone convertases, enabling the identification of novel bioactive peptides. Using this approach, we identified a 12-mer peptide, BRINP2-related peptide (BRP). When administered pharmacologically, BRP reduces food intake and exhibits anti-obesity effects in mice and pigs without inducing nausea or aversion. Mechanistically, BRP administration triggers central FOS activation and acts independently of leptin, GLP-1 receptor and melanocortin 4 receptor. Together, these data introduce a method to identify new bioactive peptides and establish pharmacologically that BRP may be useful for therapeutic modulation of body weight. Computational drug discovery is used to identify a 12-mer peptide derived from BRINP2 with potent anti-obesity effects that are independent of leptin, glucagon-like peptide 1 receptor and melanocortin 4 receptor.

ObjectiveThe colonic microbiota ferment dietary fibres, producing short chain fatty acids. Recent evidence suggests that the short chain fatty acid propionate may play an important role in appetite regulation. We hypothesised that colonic delivery of propionate would increase peptide YY (PYY) and glucagon like peptide-1 (GLP-1) secretion in humans, and reduce energy intake and weight gain in overweight adults.DesignTo investigate whether propionate promotes PYY and GLP-1 secretion, a primary cultured human colonic cell model was developed. To deliver propionate specifically to the colon, we developed a novel inulin-propionate ester. An acute randomised, controlled cross-over study was used to assess the effects of this inulin-propionate ester on energy intake and plasma PYY and GLP-1 concentrations. The long-term effects of inulin-propionate ester on weight gain were subsequently assessed in a randomised, controlled 24-week study involving 60 overweight adults.ResultsPropionate significantly stimulated the release of PYY and GLP-1 from human colonic cells. Acute ingestion of 10 g inulin-propionate ester significantly increased postprandial plasma PYY and GLP-1 and reduced energy intake. Over 24 weeks, 10 g/day inulin-propionate ester supplementation significantly reduced weight gain, intra-abdominal adipose tissue distribution, intrahepatocellular lipid content and prevented the deterioration in insulin sensitivity observed in the inulin-control group.ConclusionsThese data demonstrate for the first time that increasing colonic propionate prevents weight gain in overweight adult humans.Trial registration numberNCT00750438.

The formylpeptide receptors (FPRs) mediate pattern recognition of formylated peptides derived from invading pathogens or mitochondria from dead host cells. They can also sense other structurally distinct native peptides and even lipid mediators to either promote or resolve inflammation. Pharmacological targeting of FPRs represents a novel therapeutic approach in treating inflammatory diseases. However, the molecular mechanisms underlying FPR ligand recognition are elusive. We report cryo-EM structures of G i -coupled FPR1 and FPR2 bound to a formylpeptide and G i -coupled FPR2 bound to two synthetic peptide and small-molecule agonists. Together with mutagenesis data, our structures reveal the molecular mechanism of formylpeptide recognition by FPRs and structural variations of FPR1 and FPR2 leading to their different ligand preferences. Structural analysis also suggests that diverse FPR agonists sample a conserved activation chamber at the bottom of ligand-binding pockets to activate FPRs. Our results provide a basis for rational drug design on FPRs. Zhuang et al. report four cryo-EM structures of formylpeptide receptors FPR1 and FPR2 coupled with Gi protein and diverse agonists, revealing how FPRs as pattern recognition receptors recognize formylpeptides and synthetic agonists and a distinctive receptor activation mechanism.

Proline-rich antimicrobial peptides (PrAMPs) inhibit bacterial protein biosynthesis by binding to the polypeptide exit tunnel (PET) near the peptidyl transferase center. Api137, an optimized derivative of honeybee PrAMP apidaecin, inhibits protein expression by trapping release factors (RFs), which interact with stop codons on ribosomes to terminate translation. This study uses cryo-EM, functional assays and molecular dynamic (MD) simulations to show that Api137 additionally occupies a second binding site near the exit of the PET and can repress translation independently of RF-trapping. Api88, a C-terminally amidated (-CONH 2 ) analog of Api137 (-COOH), binds to the same sites, occupies a third binding pocket and interferes with the translation process presumably without RF-trapping. In conclusion, apidaecin-derived PrAMPs inhibit bacterial ribosomes by multimodal mechanisms caused by minor structural changes and thus represent a promising pool for drug development efforts. Proline-rich antimicrobial peptides (PrAMPs) inhibit bacterial protein biosynthesis. Here, the authors show that the honey-bee derived PrAMPs Api137 and Api88 inhibit bacterial ribosomes through multiple mechanisms, promising for drug development.

Diet is among the most important factors contributing to intestinal homeostasis, and basic functions performed by the small intestine need to be tightly preserved to maintain health. Little is known about the direct impact of high-fat (HF) diet on small-intestinal mucosal defenses and spatial distribution of the microbiota during the early phase of its administration. We observed that only 30 d after HF diet initiation, the intervillous zone of the ileum-which is usually described as free of bacteria-became occupied by a dense microbiota. In addition to affecting its spatial distribution, HF diet also drastically affected microbiota composition with a profile characterized by the expansion of Firmicutes (appearance of Erysipelotrichi), Proteobacteria (Desulfovibrionales) and Verrucomicrobia, and decrease of Bacteroidetes (family S24-7) and Candidatus arthromitus A decrease in antimicrobial peptide expression was predominantly observed in the ileum where bacterial density appeared highest. In addition, HF diet increased intestinal permeability and decreased cystic fibrosis transmembrane conductance regulator (Cftr) and the Na-K-2Cl cotransporter 1 (Nkcc1) gene and protein expressions, leading to a decrease in ileal secretion of chloride, likely responsible for massive alteration in mucus phenotype. This complex phenotype triggered by HF diet at the interface between the microbiota and the mucosal surface was reversed when the diet was switched back to standard composition or when mice were treated for 1 wk with rosiglitazone, a specific agonist of peroxisome proliferator-activated receptor-γ (PPAR-γ). Moreover, weaker expression of antimicrobial peptide-encoding genes and intervillous bacterial colonization were observed in Ppar-γ-deficient mice, highlighting the major role of lipids in modulation of mucosal immune defenses.