抗菌肽药物工程化技术研究进展

尽管抗生素在畜牧业疾病防治中的主导地位在短期内不会动摇,但病原菌耐药性形成与快速发展让抗菌肽成为近年新药研发热点之一。作为一种在生物体内广泛存在的天然免疫物质,抗菌肽具有抗菌、抗病毒、抗肿瘤和免疫调节等功能,由于药效短、对蛋白酶敏感、细胞毒性高等缺陷而限制其应用。本文综述了抗菌肽基因工程技术、聚乙二醇(PEG)化、靶向性改造和固定化等工程技术在抗菌肽新药开发中的应用研究进展,以促进抗菌肽产业化。     

Molecular diversity and evolution of myticin-C antimicrobial peptide variants in the Mediterranean mussel, Mytilus galloprovincialis

Mussels have diverse groups of cysteine rich, cationic antimicrobial peptides (AMPs) (defensins, mytilins, myticins, and mytimycin) that constitute an important component of their innate immune defence. Despite the identification and characterization of these AMPs in mussels, the underlying genetic mechanisms that maintain high diversity among multiple variants of the myticin-C isoform are poorly understood. Using phylogeny-based models of sequence evolution and several site-by-site frequency spectrum statistical tests for neutrality, herein we report that positive selection has been the major driving force in maintaining high diversity among the allelic-variants of the myticin-C AMP of Mytilus galloprovincialis. The statistical tests rejected the hypothesis that all polymorphism within myticin-C loci is neutral. Although a majority of the codons constrained to purifying selection (rate of amino acid replacement to the silent substitution, omega < 1), approximately 8% of the codons with omega approximately equal to 5.5 are under positive selection (omega > 1), thus indicating adaptive evolution of certain amino acids. Direct interaction of these peptides with the surrounding pathogens and/or altered/new pathogens in the changing environment is the likely cause of molecular adaptation of certain amino acid sites in myticin-C variants.     

A review of fish-derived antioxidant and antimicrobial peptides: their production, assessment, and applications

Fishes are rich sources of structurally diverse bioactive compounds. In recent years, much attention has been paid to the existence of peptides with biological activities and proteins derived from foods that might have beneficial effects for humans. Antioxidant and antimicrobial peptides isolated from fish sources may be used as functional ingredients in food formulations to promote consumer health and improve the shelf life of food products. This paper presents an overview of the antioxidant and antimicrobial peptides derived from various fishes. In addition, we discuss the extraction of fish proteins, enzymatic production, and the techniques used to isolate and characterize these compounds. Furthermore, we review the methods used to assay the bioactivities and their applications in food and nutraceuticals.     

Structural determinants of host defense peptides for antimicrobial activity and target cell selectivity

Antimicrobial host defense peptides (HDPs) are a critical component of the innate immunity with microbicidal, endotoxin-neutralizing, and immunostimulatory properties. HDPs kill bacteria primarily through non-specific membrane lysis, therefore with a less likelihood of provoking resistance. Extensive structure–activity relationship studies with a number of HDPs have revealed that net charge, amphipathicity, hydrophobicity, and structural propensity are among the most important physicochemical and structural parameters that dictate their ability to interact with and disrupt membranes. A delicate balance among these factors, rather than a mere alteration of a single factor, is critically important for HDPs to ensure the antimicrobial potency and target cell selectivity. With a better understanding of the structural determinants of HDPs for their membrane-lytic activities, it is expected that novel HDP-based antimicrobials with minimum toxicity to eukaryotic cells can be developed for resistant infections, which have become a global public health crisis.     

含抗菌肽酵母工程菌对肉仔鸡肠道菌群和免疫功能的影响

目的 研究含抗菌肽（Cec Md、3cs、3js）酵母工程菌对肉仔鸡肠道菌群和免疫功能的影响。方法 采用随机试验设计的方法,选用1日龄健康爱拔益加肉仔鸡400只,随机分成5组,每组设4个重复,每个重复20只鸡（雌雄各半）。空白对照组常规饮水,抗生素组在饮水中添加50 mg/L的泰乐菌素,抗菌肽实验组分别在饮水中添加8 mg/L含Cec Md、3cs和3js酵母工程菌,实验期42 d。结果 （1）Cec Md组的第1、4和5周及3cs组第3、5周的大肠埃希菌数量显著低于空白对照组（P<0.05）;Cec Md组和3cs组的第2至第6周及3js组的第2至第4周沙门菌数量显著低于空白对照组（P<0.05）;Cec Md组的第4至第6周及3cs组和3js组的第5周的乳杆菌数量显著高于空白对照组（P<0.05）;Cec Md组的第2、3、5周和6周及3cs组第5、6周及3js组的第3至第6周的双歧杆菌数量显著高于空白对照组（P<0.05）。（2）Cec Md组的第3、5周及3cs和3js组的第6周的IgA含量显著高于空白对照组（P<0.05）;Cec Md组和3js组的第3周的IgG含量显著高于空白对照组（P<0.05）。3js组的第1周的IgM含量显著高于空白对照组（P<0.05）,Cec Md组第4、5周的IgE含量显著高于空白对照组（P<0.05）。结论 含抗菌肽Cec Md、3cs和3js酵母工程菌可以抑制肉仔鸡肠道有害菌群的生长,促进其有益菌群的增殖,且可以改善肉仔鸡的免疫功能。     

Avian antimicrobial peptides: the defense role of beta-defensins

Avian antimicrobial peptides, classified as beta-defensins, have been identified from bloods of chicken, turkey, and ostrich; epithelial cells of chicken and turkey; and king penguin stomach contents. Beta-defensins are a family of antimicrobial peptides characterized by six cysteine residues forming beta-defensin motifs that are also found in bovine, ovine, pig, and human. These peptides are active against a wide range of microorganisms including Gram-positive and Gram-negative bacteria, fungi, and yeast. Analysis of evolutionary relationships of vertebrate beta-defensins showed that there might be a common ancestral gene between avian and other mammalian peptides. This ancient gene may have been passed down and evolved from species older than the oldest living birds, forming a beta-defensin-like precursor molecule. This review describes potential applications of these peptides in health care products.     

Driving engineering of novel antimicrobial peptides from simulations of peptide-micelle interactions

Simulations of antimicrobial peptides in membrane mimics can provide the high resolution, atomistic picture that is necessary to decipher which sequence and structure components are responsible for activity and toxicity. With such detailed insight, engineering new sequences that are active but non-toxic can, in principle, be rationalized. Armed with supercomputers and accurate force fields for biomolecular interactions, we can now investigate phenomena that span hundreds of nanoseconds. Although the phenomena involved in antimicrobial activity, (i.e., diffusion of peptides, interaction with lipid layers, secondary structure attainment, possible surface aggregation, possible formation of pores, and destruction of the lipid layer integrity) collectively span time scales still prohibitively long for classical mechanics simulations, it is now feasible to investigate the initial approach of single peptides and their interaction with membrane mimics. In this article, we discuss the promise and the challenges of widely used models and detail our recent work on peptide-micelle simulations as an attractive alternative to peptide-bilayer simulations. We detail our results with two large structural classes of peptides, helical and beta-sheet and demonstrate how simulations can assist in engineering of novel antimicrobials with therapeutic potential.     

Molecular cloning and biological characterization of novel antimicrobial peptides, pilosulin 3 and pilosulin 4, from a species of the Australian ant genus Myrmecia

Venom of an Australian ant species of the Myrmecia pilosula species complex (mss. name Myrmecia banksi Taylor) contains two major allergenic peptides, pilosulin 1 and pilosulin 2. To obtain novel cDNA clones that encode the pilosulin-related bioactive peptides, mRNA of another Myrmecia species was subjected to RT-PCR in which the forward primer corresponds to a nucleotide sequence in the leader sequences of pilosulin 1 and pilosulin 2. As a result, we isolated cDNA clones encoding the novel antimicrobial peptides pilosulin 3 and pilosulin 4. The nucleotide and the amino acid sequences of all four pilosulins have high homology except for the mature peptide coding regions. Synthetic pilosulin 3 and pilosulin 4 peptides displayed antimicrobial activity with histamine-releasing and low hemolytic activities.     

Molecular docking analysis of antimicrobial peptides with the CXCL1 protein target for colorectal cancer

Antimicrobial peptides (AMPs) play a prominent role in drug discovery due to the rapid increase in drug resistant infections. Hence, we report the molecular docking analysis of antimicrobial peptides MREEKKERKRD and MVQGAKRGGRLHRV with the target protein CXCL1 in the context of colorectal cancer for further consideration in drug discovery.     

Overview on the recent study of antimicrobial peptides: Origins, functions, relative mechanisms and application

Antimicrobial peptides (AMPs), which are produced by several species including insects, other animals, micro-organisms and synthesis, are a critical component of the natural defense system. With the growing problem of pathogenic organisms resistant to conventional antibiotics, especially with the emergence of NDM-1, there is increased interest in the pharmacological application of AMPs. They can protect against a broad array of infectious agents, such as bacteria, fungi, parasite, virus and cancer cells. AMPs have a very good future in the application in pharmaceuticals industry and food additive. This review focuses on the AMPs from different origins in these recent years, and discusses their various functions and relative mechanisms of action. It will provide some detailed files for clinical research of pharmaceuticals industry and food additive in application.     

Tethering antimicrobial peptides: Current status and potential challenges

Antimicrobial peptides (AMPs) are next generation antibiotics which will make excellent coating agents for a myriad of devices because they are far less susceptible to the development of pathogen resistance compared to conventional antibiotics, exhibit rapid and broad-spectrum killing profiles, and are effective at low concentrations. These advantages, however, are compromised upon AMP tethering to solid supports. The effects of peptide-tethering strategies in governing AMP orientation, surface density, flexibility, and activity are reviewed. Understanding AMP structure-function relationship in the tethered conformation will enable rational improvements of immobilisation parameters. Foreseeable challenges in the development of AMP-coated devices such as microbial accumulation on implant surface and the lack of direct biomolecular structure and orientation data of peptides on surfaces are also discussed, and solutions to address these roadblocks are also proposed.     

Correlation between simulated physicochemical properties and hemolycity of protegrin-like antimicrobial peptides: predicting experimental toxicity

The therapeutic, antibiotic potential of antimicrobial peptides can be prohibitively diminished because of the cytotoxicity and hemolytic profiles they exhibit. Quantifying and predicting antimicrobial peptide toxicity against host cells is thus an important goal of AMP related research. In this work, we present quantitative structure activity relationships for toxicity of protegrin-like antimicrobial peptides against human cells (epithelial and red blood cells) based on physicochemical properties, such as interaction energies and radius of gyration, calculated from molecular dynamics simulations of the peptides in aqueous solvent. The hypothesis is that physicochemical properties of peptides, as manifest by their structure and interactions in a solvent and as captured by atomistic simulations, are responsible for their toxicity against human cells. Protegrins are beta-hairpin peptides with high activity against a wide variety of microbial species, but in their native state are toxic to human cells. Sixty peptides with experimentally determined toxicities were used to develop the models. We test the resulting relationships to determine their ability to predict the toxicity of several protegrin-like peptides. The developed QSARs provide insight into the mechanism of cytotoxic action of antimicrobial peptides. In a subsequent blind test, the QSAR correctly ranked four of five protegrin analogues newly synthesized and tested for toxicity.     

Ribosomally synthesized antimicrobial peptides: their function, structure, biogenesis, and mechanism of action

Ribosomally synthesized peptides with antimicrobial activity are produced by prokaryotes, plants, and a wide variety of animals, both vertebrates and invertebrates. These peptides represent an important defense against micro-organisms. Although the peptides differ greatly in primary structures, they are nearly all cationic and very often amphiphilic, which reflects the fact that many of these peptides kill their target cells by permeabilizing the cell membrane. Moreover, many of these peptides may roughly be placed into one of three groups: (1) those that have a high content of one (or two) amino acid(s), often proline, (2) those that contain intramolecular disulfide bonds, often stabilizing a predominantly β-sheet structure, and (3) those with amphiphilic regions if they assume an α-helical structure. Most known ribosomally synthesized antimicrobial peptides have been identified and characterized during the past 15 years. As a result of these studies, insight has been gained into fundamental aspects of biology and biochemistry such as innate immunity, membrane-protein interactions, and protein modification and secretion. Moreover, it has become evident that these peptides may be developed into useful antimicrobial additives and drugs. This review presents a broad overview of the main types of ribosomally synthesized antimicrobial peptides produced by eukaryotes and prokaryotes. Received: 30 August 1996 / Accepted: 26 November 1996     

Molecular evolution of animal antimicrobial peptides: widespread moderate positive selection

An increasing number of studies in both vertebrates and invertebrates show that the evolution of antimicrobial peptides is driven by positive selection. Because these diverse molecules show potential for therapeutic applications, they are currently the targets of much structural and functional research, providing extensive background data for evolutionary studies. In this paper, patterns of molecular evolution in antimicrobial peptide genes are reviewed. Evidence for positive selection on antimicrobial peptides includes an excess of nonsynonymous nucleotide substitutions, an excess of charge-changing amino acid substitutions, nonneutral patterns of allelic variation, and functional assays in vivo and in vitro that show improved antimicrobial effects for derived sequence variants. Positive selection on antimicrobial peptides may be as common as, but perhaps weaker than, selection on the best-known example of adaptively evolving immunity genes, the major histocompatibility complex. Thus, antimicrobial peptides present a useful and underutilized model for the study of adaptive molecular evolution.     

Effect of physicochemical properties of peptides from soy protein on their antimicrobial activity

Antimicrobial peptides (AMPs) kill microbial cells through insertion and damage/permeabilization of the cytoplasmic cell membranes and has applications in food safety and antibiotic replacement. Soy protein is an attractive, abundant natural source for commercial production of AMPs. In this research, explicit solvent molecular dynamics (MD) simulation was employed to investigate the effects of (i) number of total and net charges, (ii) hydrophobicity (iii) hydrophobic moment and (iv) helicity of peptides from soy protein on their ability to bind to lipid bilayer and their transmembrane aggregates to form pores. Interaction of possible AMP segments from soy protein with 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine/1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol (POPC/POPG) bilayers, a mimic of bacterial cell membrane, was investigated. Pore formation was insensitive to helicity and occurred for hydrophobicity threshold in the range of −0.3–0 kcal/mol, hydrophobic moment threshold of 0.3 kcal/mol, net charge threshold of 2. Though low hydrophobicity and high number of charges help in the formation of water channel for transmembrane aggregates, insertion of peptides with these properties requires overcome of energy barrier, as shown by potential of mean force calculations, thereby resulting in low antimicrobial activity. Experimental evaluation of antimicrobial activity of these peptides against Gram positive L. monocytogenes and Gram negative E. coli as obtained by spot-on-lawn assay was consistent with simulation results. These results should help in the development of guidelines for selection of peptides with antimicrobial activity based on their physicochemical properties.     

抗菌肽抗菌机制及其应用研究进展

抗菌肽是一类小分子肽,具有广谱的抗菌活性。以往对抗菌肽抗菌机制的研究主要集中在细菌细胞膜的作用上,包含"桶板"模型、"毯式"模型,"环形孔"模型和"凝聚"模型。近年来相继发现某些抗菌肽可以作用于细菌细胞内部,与核酸物质结合,阻断DNA复制、RNA合成;影响蛋白质合成;抑制隔膜、细胞壁合成,阻碍细胞分裂;抑制胞内酶的活性。本文从胞内机制和胞外机制两个角度对抗菌肽的抗菌机制进行综述,以期阐明各类抗菌肽的作用机制,为进一步研究菌株耐药性、杀菌效果及其杀菌机制提供科学根据。     

Cathelicidin family of antimicrobial peptides: proteolytic processing and protease resistance

Cathelicidins are a gene family of antimicrobial peptides produced as inactive precursors. Signal peptidase removes the N-terminal signal sequence, while peptidylglycine alpha-amidating monooxygenase often amidates and cleaves the C-terminal region. Removal of the cathelin domain liberates the active antimicrobial peptide. For mammalian sequences, this cleavage usually occurs through the action of elastase, but other tissue-specific processing enzymes may also operate. Once released, these bioactive peptides are susceptible to proteolytic degradation. We propose that some mature cathelicidins are naturally resistant to proteases due to their unusual primary structures. Among mammalian cathelicidins, proline-rich sequences should resist attack by serine proteases because proline prevents cleavage of the scissile bond. In hagfish cathelicidins, the unusual amino acid bromotryptophan may make the active peptides less susceptible to proteolysis for steric reasons. Such protease resistance could extend the pharmacokinetic lifetimes of cathelicidins in vivo, sustaining antimicrobial activity.     

Medusins: A new class of antimicrobial peptides from the skin secretions of phyllomedusine frogs

Natural drug discovery represents an area of research with vast potential. The investigation into the use of naturally-occurring peptides as potential therapeutic agents provides a new “chemical space” for the procurement of drug leads. Intensive and systematic studies on the broad-spectrum antimicrobial peptides found in amphibian skin secretions are of particular interest in the quest for new antibiotics to treat multiple drug-resistant bacterial infections. Here we report the molecular cloning of the biosynthetic precursor-encoding cDNAs and respective mature peptides representing a novel group of antimicrobial peptides from the skin secretions of representative species of phyllomedusine leaf frogs: the Central American red-eyed leaf frog (Agalychnis callidryas), the South American orange-legged leaf frog (Phyllomedusa hypochondrialis) and the Giant Mexican leaf frog (Pachymedusa dacnicolor). Each novel peptide possessed the highly-conserved sequence, LGMIPL/VAISAISA/SLSKLamide, and each exhibited activity against the Gram-positive bacterium, Staphylococcus aureus and the yeast, Candida albicans, but all were devoid of haemolytic effects at concentrations up to and including the MICs for both organisms. The novel peptide group was named medusins, derived from the name of the hylid frog sub-family, Phyllomedusinae, to which all species investigated belong. These data clearly demonstrate that comparative studies of the skin secretions of phyllomedusine frogs can continue to produce novel peptides that have the potential to be leads in the development of new and effective antimicrobials.     

Purification and characterization of antimicrobial and vasorelaxant peptides from skin extracts and skin secretions of the North American pig frog Rana grylio

Eight peptides with differential growth–inhibitory activity against the gram-positive bacterium Staphylococcus aureus, the gram-negative bacterium Escherichia coli and the yeast, Candida albicans were isolated from an extract of the skin of the North American pig frog Rana grylio. The primary structures of these antimicrobial peptides were different from previously characterized antimicrobial peptides from Ranid frogs but on the basis of sequence similarities, the peptides may be classified as belonged to four previously characterized peptide families: the ranatuerin-1, ranatuerin-2 and ranalexin families, first identified in the North American bullfrog, Rana catesbeiana, and the temporin family first identified in the European common frog Rana temporaria. Peptides belonging to the brevinin-1, brevinin-2, esculentin-1, and esculentin-2 families, previously isolated from the skins of other species of Ranid frogs, were not identified in the extracts. The ranatuerin-1 and ranalexin peptides showed broadest spectrum of antimicrobial activity whereas the temporins were active only against S. aureus. Synthetic replicates of temporin-1Gb (SILPTIVSFLSKFL.NH₂) and temporin-1Gd (FILPLIASFLSKFL.NH₂) produced concentration-dependent relaxation of preconstricted vascular rings from the rat thoracic aorta (EC₅₀=2.4±0.1 μM for temporin-1Gb and 2.3±0.2 μM for temporin-1Gd). The antimicrobial peptides that were isolated in extracts of the skin R. grylio were present in the same molecular forms in electrically-stimulated skin secretions of the animal demonstrating that the peptides are stored in the granular glands of the skin in their fully processed forms.