抗菌肽及其功能研究

抗菌肽是近年来发现的广泛存在于自然界的一类阳离子抗菌活性肽,越来越多的证据表明它们在宿主先天性免疫和适应性免疫中有着重要的作用。对抗菌肽的研究正不断深入。本文先从抗菌肽研究的历史背景出发,简要介绍了抗菌肽的一般特性;然后从抗菌肽的直接抗菌活性和免疫调节功能这两个方面重点阐述其在宿主防御过程中的作用,最后对抗菌肽的临床应用及前景做了一个概述。     

昆虫防御机制研究的一些进展

昆虫是动物界中最大的种群,遍布陆地、江河、海洋和天空,且有惊人的繁殖力和对环境顽强的适应性。研究昆虫的防御体系,对害虫的防治及经济昆虫的保护都有理论和实践意义。十九世纪人们已发现昆虫的免疫现象。例如接种微量的病原菌可诱导提高机体的抗病力。但诱导源是非专一性的,免疫应答又是广谱的;昆虫不同于高等动物;它们不产生抗体r-球蛋白,而是以抗菌肽、抗病毒因子、凝集素、溶菌酶及蛋白酶抑制剂等多种活性因子,配合多种功能的血细胞以建立一个开放的、完整的防御体系。本文扼要地从抗菌肽和抗病毒因子两个方面综述昆虫防御机制研究的进展。 (一)抗菌肽 1976年,瑞典博曼(Boman)等人从地中海果蝇及惜古比天蚕血淋巴中分离到抗菌肽,称天蚕素(Ce-     

昆虫抗菌肽对病原微生物作用的研究进展

在诱导和非诱导情况下,昆虫能产生各种类型的具有体液免疫功能的小分子物质-抗菌肽,参与机体对入侵病原微生物的免疫应答反应,构成了机体独特的免疫系统和免疫机制。这类抗菌肽或抗菌蛋白也存在于其它动物。研究表明,抗菌肽对细菌、真菌、病毒和原虫都具有作用,甚至对癌细胞也具有杀伤作用。随着抗菌肽家族的不断扩大,其结构研究的深入,相继提出了一些崭新的杀菌方式和作用机制。本文从目前国内外这方面的研究入手,分析各抗菌肽的作用特点、杀菌作用模式,展望了基因工程及临床应用的前景。     

昆虫天然免疫反应研究前沿

昆虫天然免疫反应分为体液免疫和细胞免疫两种,二者共同作用抵御细菌、真菌、病毒等外源病原物的侵染。体液免疫反应主要包括黑色素形成和抗菌肽产生两种机制,细胞免疫反应包括吞噬、集结和包囊等作用类型。在昆虫天然免疫反应中,昆虫模式识别蛋白负责识别并结合外源物表面特有的模式分子,丝氨酸蛋白酶、丝氨酸蛋白酶抑制剂、各种配体、受体等负责级联信号途径的激活和调控,抗菌肽、黑色素等效应分子则负责对入侵物的杀灭和清除。本文根据国外和作者自己的研究,综述了昆虫天然免疫反应的研究进展,并针对该领域最新的研究动态展望了昆虫肠道免疫、昆虫免疫致敏以及不完全变态昆虫免疫学等这些研究前沿。     

泛素-蛋白酶体系统在昆虫先天免疫中的调控作用

完善的先天免疫系统使得昆虫成为分布最广、适应性最强、物种多样性最丰富的动物类群。在长期的进化过程中,昆虫建立了一套安全有效的先天免疫系统,一方面在面对外界微生物攻击的时候及时有效的发生免疫应答反应;另一方面通过免疫抑制来调控适度免疫应答,避免对自身发动攻击和控制环境共生菌刺激引起的免疫应答信号通路的持续激活。泛素-蛋白酶体系统在昆虫先天免疫中具有重要的调控作用,在Toll和IMD信号通路中,通过对免疫应答通路中信号分子的泛素化修饰加工,促进或抑制抗菌肽的表达,从而使免疫反应达到一个平衡。本文通过对泛素-蛋白酶体系统在Toll和IMD信号通路中的免疫应答和免疫抑制方面的研究进行综述,阐明了该系统在昆虫先天免疫中的调控作用,将有助于开展农业害虫与其天敌之间相互关系的深入研究,揭示其免疫调控机理,为开发生物农药,进行生物防控提供理论依据。     

昆虫抗菌肽的研究进展

昆虫抗菌肽是昆虫先天免疫中起重要的作用的一类免疫效应因子,具有广谱抗菌、抗病毒、抑制肿瘤的生物活性和很好应用前景.本文主要介绍昆虫抗菌肽的类型、抗菌机理和分子设计的研究进展.     

抗菌肽的抗肿瘤作用

抗菌肽是宿主免疫防御系统的重要成分,具有广谱杀菌、相对分子量较小、热稳定性及水溶性好等优点,更重要的是抗菌肽能选择性杀灭肿瘤细胞,对人畜毒副作用小。因此,抗菌肽在生物和医药等方面,尤其是抗肿瘤方面有很好的开发前景。     

昆虫天然免疫反应分子机制研究进展

昆虫体内缺乏高等脊椎动物所具有的获得性免疫系统, 只能依赖发达的天然免疫系统抵抗细菌、 真菌、 病毒等外源病原物的侵染。本文概括了昆虫天然免疫反应发生和作用的分子机制相关进展, 重点阐述了重要免疫相关因子在昆虫天然免疫反应中的功能和作用机制。昆虫天然免疫反应分为体液免疫和细胞免疫两种, 二者共同作用完成对病原物的吞噬 (phagocytosis)、 集结 (nodulation)、 包囊 (encapsulation)、 凝结 (coagulation)和黑化（melanization）等。当昆虫受到外界病原物的侵染时, 首先通过体内的模式识别蛋白（pattern recognition proteins/receptor, PRPs）识别并结合病原物表面特有的模式分子（pathogen-associated molecular pattern, PAMPs）, 继而一系列包括丝氨酸蛋白酶和丝氨酸蛋白酶抑制剂在内的级联激活反应被激活和调控, 产生抗菌肽、 黑色素等免疫效应分子, 清除或杀灭外源物。抗菌肽是一类小分子量的阳离子肽, 具有广谱抗菌活性, 针对不同类型的病原物, 抗菌肽的产生机制也不尽相同。昆虫体内存在着两种信号转导途径调节抗菌肽的产生： 一是由真菌和大部分革兰氏阳性菌激活的Toll途径; 二是由革兰氏阴性菌激活的Imd途径（immune deficiency pathway）。这两个途径通过激活不同转录因子调控不同抗菌肽基因的表达参与昆虫体内的天然免疫反应。     

某些抗菌肽的研究进展

抗菌肽是各种生物防御系统的一个组成部分,是由于微生物等因素的侵染而产生的免疫应答反应产物,具有分子量低,热稳定,强碱性和广谱抗菌等特点,抗菌肽的正电荷与细菌细胞的磷脂头负电荷之间的相互作用是重要,肽分子氮端的两性螺旋是裂解细菌的主要部分,碳末端酰胺化与抗菌肽的广谱抗菌有关,抗菌肽具有独特的抗菌机理,能在细菌质膜上形成离子通道,破坏膜势,引起胞内物质泄漏,从而杀灭细菌。     

类弹性蛋白ELPs融合表达在抗菌肽分离纯化中的应用（简报）

抗菌肽（Antimicrobial polypeptides,AMPs）是两性带电分子,广泛存在于多种生物体内,具有广谱抗菌、调节免疫、抑制肿瘤等多种生物学功能。一些抗菌肽不仅对耐药性的病原细菌有很好的抑制和杀灭作用,而且还对真菌、原生动物、病毒等有很好的抑制作用。近年研究还发现,某些抗菌肽还可选择性杀伤肿瘤细胞,     

The role of antimicrobial peptides in innate immunity

Production of antimicrobial peptides and proteins is an importantmeans of host defense in eukaryotes. The larger antimicrobialproteins, containing more than 100 amino acids, are often lyticenzymes, nutrient-binding proteins or contain sites that targetspecific microbial macromolecules. The smaller antimicrobialpeptides act largely by disrupting the structure or functionof microbial cell membranes. Hundreds of antimicrobial peptideshave been found in the epithelial layers, phagocytic cells andbody fluids of multicellular animals, from mollusks to humans.Some antimicrobial peptides are produced constitutively, othersare induced in response to infection or inflammation. Studiesof the regulation of antimicrobial peptide synthesis in Drosophilahave been particularly fruitful, and have provided a new paradigmfor the analysis of mammalian host defense responses. It nowappears that the general patterns of antimicrobial responsesof invertebrates have been preserved in vertebrates ("innateimmunity") where they contribute to host defense both independentlyand in complex interplay with adaptive immunity.     

Antimicrobial activity and stability to proteolysis of small linear cationic peptides with D-amino acid substitutions

Antimicrobial peptides contribute to innate host defense against a number of bacteria and fungal pathogens. Some of antimicrobial synthetic peptides were systemically administered in vivo; however, effective protection has so far not been obtained because the effective dose of peptides in vivo seems to be very high, often close to the toxic level against the host. Alternatively, peptides administered in vivo may be degraded by certain proteases present in serum. In this study, D-amino acids were substituted for the L-amino acids of antimicrobial peptides to circumvent these problems. Initially a peptide (L-peptide) rich in five arginine residues and consisting of an 11-amino acid peptide (residues 32-42) of human granulysin was synthesized. Subsequently, the L-amino acids of the 11-amino acid peptide were replaced partially (D-peptide) or wholly (AD-peptide) with D-amino acids. Activity and stability to proteolysis, in particular, in the serum of antimicrobial peptides with D-amino acid substitutions were examined. Peptides with D-amino acid substitutions were found to lyse bacteria as efficiently as their all-L-amino acid parent, L-peptide. In addition, the peptide composed of L-amino acids was susceptible to trypsin, whereas peptides containing D-amino acid substitutions were highly stable to trypsin treatment. Similarly, the peptide consisting of L-amino acids alone was also susceptible to fetal calf serum (FCS), however, protease inhibitors restored the lowered antimicrobial activity of the FCS-incubated peptide. Thus, D-amino acid substitutions can make antimicrobial peptides resistant to proteolysis, suggesting that the antimicrobial peptides consisting of D-amino acids are potential candidates for clinical therapeutic use.     

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.     

Allergic airway inflammation inhibits pulmonary antibacterial host defense

The innate immune system of the lung is a multicomponent host defense system and in addition has an instructing role in regulating the quality and quantity of the adaptive immune response. When the interaction between innate and adaptive immunity is disturbed, pathological conditions such as asthma can develop. It was the aim of the study to investigate the effect of the allergic inflammation of the lung on the innate host defense during bacterial infection. Human bronchial epithelial cells were preincubated with Th2 cytokines and infected with Pseudomonas aeruginosa. The effect of the Th2 cytokines on the mRNA levels of antimicrobial peptides and the antimicrobial activity of HBEC was determined. To investigate the influence of an allergic inflammation on pulmonary host defense in vivo, mice sensitized and challenged with OVA were infected with P. aeruginosa, and the number of viable bacteria in the lungs was determined together with markers of inflammation like cytokines and antimicrobial peptides. Exposure of airway epithelial cells to Th2 cytokines resulted in a significantly decreased antimicrobial activity of the cells and in suppressed mRNA levels of the antimicrobial peptide human beta-defensin 2. Furthermore, mice with allergic airway inflammation had significantly more viable bacteria in their lungs after infection. This was consistent with reduced levels of proinflammatory cytokines and of the antimicrobial peptide cathelin-related antimicrobial peptide. These results show that an allergic airway inflammation suppresses the innate antimicrobial host defense. The adaptive immune system modulates the functions of the pulmonary innate immune system.     

Cateslytin,a Chromogranin A Derived Peptide Is Active against Staphylococcus aureus and Resistant to Degradation by Its Proteases

Innate immunity involving antimicrobial peptides represents an integrated and highly effective system of molecular and cellular mechanisms that protects host against infections. One of the most frequent hospital-acquired pathogens, Staphylococcus aureus, capable of producing proteolytic enzymes, which can degrade the host defence agents and tissue components. Numerous antimicrobial peptides derived from chromogranins, are secreted by nervous, endocrine and immune cells during stress conditions. These kill microorganisms by their lytic effect at micromolar range, using a pore-forming mechanism against Gram-positive bacteria, filamentous fungi and yeasts. In this study, we tested antimicrobial activity of chromogranin A-derived peptides (catestatin and cateslytin) against S. aureus and analysed S. aureus-mediated proteolysis of these peptides using HPLC, sequencing and MALDI-TOF mass spectrometry. Interestingly, this study is the first to demonstrate that cateslytin, the active domain of catestatin, is active against S. aureus and is interestingly resistant to degradation by S. aureus proteases.     

Antibiotic peptides from higher eukaryotes: biology and applications.

Gene-encoded antibiotic peptides are increasingly being recognized as effector molecules of host defense in plants and animals. Studies of antimicrobial peptides are providing new insights into the dynamic interactions between microbes and their hosts, and are generating new paradigms for the pathogenesis and treatment of diseases. Because antimicrobial peptides of higher eukaryotes differ structurally from conventional antibiotics produced by bacteria and fungi, they offer novel templates for pharmaceutical compounds that could be effective against increasingly resistant microbes.     

The role of amphibian antimicrobial peptides in protection of amphibians from pathogens linked to global amphibian declines

Amphibian species have experienced population declines and extinctions worldwide that are unprecedented in recent history. Many of these recent declines have been linked to a pathogenic skin fungus, Batrachochytrium dendrobatidis, or to iridoviruses of the genus Ranavirus. One of the first lines of defense against pathogens that enter by way of the skin are antimicrobial peptides synthesized and stored in dermal granular glands and secreted into the mucus following alarm or injury. Here, I review what is known about the capacity of amphibian antimicrobial peptides from diverse amphibians to inhibit B. dendrobatidis or ranavirus infections. When multiple species were compared for the effectiveness of their in vitro antimicrobial peptides defenses against B. dendrobatidis, non-declining species of rainforest amphibians had more effective antimicrobial peptides than species in the same habitat that had recently experienced population declines. Further, there was a significant correlation between the effectiveness of the antimicrobial peptides and resistance of the species to experimental infection. These studies support the hypothesis that antimicrobial peptides are an important component of innate defenses against B. dendrobatidis. Some amphibian antimicrobial peptides inhibit ranavirus infections and infection of human T lymphocytes by the human immunodeficiency virus (HIV). An effective antimicrobial peptide defense against skin pathogens appears to depend on a diverse array of genes expressing antimicrobial peptides. The production of antimicrobial peptides may be regulated by signals from the pathogens. However, this defense must also accommodate potentially beneficial microbes on the skin that compete or inhibit growth of the pathogens. How this delicate balancing act is accomplished is an important area of future research.     

Structural congruence among membrane-active host defense polypeptides of diverse phylogeny

A requisite for efficacious host defense against pathogens and predators has prioritized evolution of effector molecules thereof. A recent multidimensional analysis of physicochemical properties revealed a novel, unifying structural signature among virtually all classes of cysteine-containing antimicrobial peptides. This motif, termed the gamma-core, is seen in host defense peptides from organisms spanning more than 2.6 billion years of evolution. Interestingly, many toxins possess the gamma-core signature, consistent with discoveries of their direct antimicrobial activity. Many microbicidal chemokines (kinocidins) likewise contain iterations of the gamma-core motif, reconciling their antimicrobial efficacy. Importantly, these polypeptide classes have evolved to target and modulate biomembranes in protecting respective hosts against unfavorable interactions with potential pathogens or predators. Extending on this concept, the current report addresses the hypothesis that antimicrobial peptides, kinocidins, and polypeptide toxins are structurally congruent and share a remarkably close phylogenetic relationship, paralleling their roles in host-pathogen relationships. Analyses of their mature amino acid sequences demonstrated that cysteine-stabilized antimicrobial peptides, kinocidins, and toxins share ancient evolutionary relatedness stemming from early precursors of the gamma-core signature. Moreover, comparative 3-D structure analysis revealed recurring iterations of antimicrobial peptide gamma-core motifs within kinocidins and toxins. However, despite such congruence in gamma-core motifs, the kinocidins diverged in overall homology from microbicidal peptides or toxins. These findings are consistent with observations that chemokines are not toxic to mammalian cells, in contrast to many antimicrobial peptides and toxins. Thus, specific functions of these molecular effectors may be governed by specific configurations of structural modules associated with a common gamma-core motif. These concepts are consistent with the hypothesis that the gamma-core is an archetype determinant in polypeptides that target or regulate with biological membranes, with specific iterations optimized to unique or cognate host defense contexts. Quantitative and qualitative data suggest these protein families emerged through both parallel and divergent processes of modular evolution. Taken together, the current and prior findings imply that the gamma-core motif contributes to conserved structures and functions of host defense polypeptides. The presence of this unifying molecular signature in otherwise diverse categories of membrane-active host defense peptides implies an ancient and essential role for such a motif in effector molecules governing host-pathogen relationships.     

Human antimicrobial peptides: analysis and application

Antimicrobial peptides are innate host defense molecules that have a direct effect on bacteria, fungi and enveloped viruses. They are found in evolutionarily diverse species ranging from prokaryotes and plants to invertebrate and vertebrate animals. Humans express several families of antimicrobial peptides in myeloid cells and on various epithelial surfaces where they are poised to defend against pathogens. Recently, antimicrobial peptides from animals and plants have served as templates for the design of new therapeutic antibiotics. This review provides an introduction to the biology of human antimicrobial peptides, followed by a more detailed discussion of their isolation from tissues and biological fluids, their purification by gel electrophoresis and chromatography and assays of their antimicrobial activities.