细菌锌离子调控体系与感染北大核心CSCD

锌(Zn)是生命体不可或缺的微量元素,对细菌和宿主同等重要。细菌体内锌离子稳态的维持依赖锌离子转运和调控体系。宿主通过限制锌离子或高锌离子中毒来控制细菌感染。为了在宿主体内生存,细菌必须表达高亲和力的锌离子转运系统,如ZnuABC,以获取足够的锌离子。由于锌与细菌大量的代谢和毒性通路密切相关,在细菌建立感染的过程中尤为重要,因此通过抑制锌离子转运系统来影响锌离子的稳态,将成为一个非常有发展前途的新型抗菌策略。     

锰离子转运、代谢与稳态平衡调控

金属离子在生命体细胞内的转运、代谢、稳态平衡调控及其相关疾病的研究是生物无机化学、化学生物学和生物医学等研究领域的一个前沿热点。锰被称作“细胞护卫”或“生命体保镖”,在生物体中发挥重要的作用,体内锰离子的含量必须维持在一个恰当的水平,锰缺少或过量都会导致疾病或生物毒性。因此,生物体内锰离子的稳态平衡调控对维持体内锰离子的正常生理功能至关重要。对细菌、出芽酵母、动物的锰离子运输、代谢及其稳态平衡调控的分子机制研究分别进行综述。     

金属离子铁和锌对鲍曼不动杆菌的抗菌作用机制研究进展

由于抗菌药物的开发周期越来越长,远远赶不上细菌耐药的发展速度,临床鲍曼不动杆菌多重耐药与泛耐药现象日益严重。因此,人们越来越关注对抗菌药物以外的抗菌物质的开发,尤其是从生存条件方面来研究抑制耐药菌活性的方法,如金、银、铜等金属离子对鲍曼不动杆菌的作用。本文主要综述铁、锌等金属离子及其螯合物对鲍曼不动杆菌的抗菌作用。铁、锌等金属离子通过与一系列酶的协同作用,调控外排泵或影响生物膜形成及其黏附性等来抑制细菌生长。此外,一些非必需金属如金、银、钯等对鲍曼不动杆菌也具有很强的毒性,有良好的抗菌和降低耐药率的效果,可作为医疗留置器械的抗菌涂层等来预防感染。     

希瓦氏菌铁稳态及调控的研究进展

铁元素通常以蛋白辅因子的形式参与一系列重要的生命过程,是绝大多数生命必需的营养物质。在细菌生命过程中,一方面铁短缺是必须克服的严峻挑战,另一方面铁过量又会危及生命。铁的这种二元性质要求细菌必须严格保持体内的铁稳态。当前革兰氏阴性菌铁稳态的作用模式及理解主要基于肠道细菌大肠杆菌的长期探索成果。近年来,在环境细菌中开展的相关研究揭示了革兰氏阴性菌的铁稳态机制存在出乎意料的多样性:细菌中铁稳态相关的生物途径及组成蛋白、关键调控系统的生理影响以及铁稳态与其他生物过程的相互影响等方面都显示不同菌种的生存和进化特征。本综述以希瓦氏菌中的相关发现为基础,分析总结革兰氏阴性菌铁稳态重要途径及其组成的多样性、不同途径的相互影响以及调控因子的生理影响和调控机理等方面的研究进展和未解决的问题,以期为革兰氏阴性菌铁稳态的研究提供参考。     

铜稳态对铁代谢平衡的影响

铜是人体必需的微量元素,参与体内多种蛋白和酶的组成,机体内存在严格的铜稳态调控机制。作为血浆中最主要的多铜亚铁氧化酶——铜蓝蛋白,与另外两种同源亚铁氧化酶——膜铁转运辅助蛋白和zyklopen,共同参与体内铁的转运,维持铁代谢的平衡。将对调节铜和铁平衡的重要意义以及铜和铁在机体代谢过程中的相互作用、发展动态进行讨论。     

细菌锌离子抗性机制研究进展

锌(Zn)是生命代谢中重要的微量金属元素,但锌过量会对细胞造成毒害作用。细菌通过一些特有的机制来解除重金属离子对它们的毒害。该文重点介绍了细菌对高浓度Zn2+的抗性机制,主要包括外排机制(RND蛋白家族、CDF蛋白家族和P-型ATPase)、螯合机制和外排后结合机制。通过这些机制细菌能有效控制胞内Zn2+浓度,保护其不受过量Zn2+的毒害,但抗性机制往往不依赖单一的抗性系统,而是多种系统协调作用的结果。细菌Zn2+抗性机制的研究将有助于进一步揭示生物是如何应对高浓度金属离子的胁迫及相应的适应性规律。     

铁摄取调节蛋白Fur功能和作用模式的研究进展

铁是大多数生物必需的微量元素,在健康和疾病,尤其是宿主-病原菌互作过程中发挥着至关重要的作用.细菌胞内铁离子浓度的高低不仅是调节自身高亲和力铁运输系统表达的信号,更是病原菌产生毒素和其他必要毒力因子的关键调控因素.而另一方面,超负荷的铁也会导致致命的细胞毒性.因此,生物体内铁稳态的维持受到严格控制,其中以铁摄取调节蛋白(ferric uptake regulator,Fur)的作用最为显著,其调控网络涵盖了细菌生命活动的各个方面.本综述将基于Fur的生物学功能,围绕其家族分类、结构特点和差异、调控网络和调控机制等方面进行总结和分析,以期为Fur和铁稳态调节等研究提供参考.     

细菌铁离子摄取系统与宿主免疫

铁是绝大多数细菌生存所必需的营养物质,参与了许多重要的生命过程。病原菌为了在宿主体内生长繁殖建立感染,进化出了多种从宿主体内摄取铁元素的机制。但过量的铁也会通过Fenton反应对细胞产生毒性,所以铁的摄取必须受到严格的调控。宿主为抵抗感染采取多种手段限制病原菌对于自身铁的利用,同时铁摄取系统也可以作为抗菌治疗的靶点。     

革兰氏阴性菌锌摄取机制及抵抗宿主营养免疫的策略

锌是一种重要的金属元素,不仅充当许多蛋白质和酶的辅因子,还广泛参与糖类、脂质等的代谢过程。锌通常以二价离子的形式存在,在自然界主要分布在植物、土壤和水中,而在生物体内则是分散于肌肉和骨等组织中。对于大多数革兰氏阴性菌而言,锌离子也是其生长过程中必不可少的营养物质。正常情况下,细菌通过ZnuABC和ZIP锌转运系统从宿主体内夺取锌离子,用于体内蛋白质和酶的合成。当过多的锌离子被摄入时,细菌为了避免锌毒性则会启动特定的锌转录调节蛋白,以维持体内外的锌平衡。另一方面,当宿主察觉体内的锌离子被夺取,便会迅速采取锌限制性营养免疫等措施来制止锌离子的进一步流失。为了抵抗宿主的营养免疫,细菌进化出了相应的抵抗策略。较为典型的例子有鲍曼不动杆菌（Acinetobacter baumannii）的锌金属伴侣ZigA,其可在低锌环境中帮助细菌转运锌离子。本文将介绍革兰氏阴性菌锌摄取机制和抵抗宿主营养免疫的典型策略,为控制细菌感染途径和开发相关免疫疫苗等方面提供理论依据。     

铜、铁离子代谢调节隐球菌致病力及宿主免疫的研究进展

金属离子参与真菌和哺乳动物众多重要的生长代谢过程。隐球菌利用金属离子参与毒力因子的形成;宿主利用金属离子进行自身代谢,增强机体免疫,抵御隐球菌感染。因此深入研究隐球菌金属离子代谢,以及探索宿主利用金属离子抵御隐球菌感染的调控机制是至关重要的,可为真菌感染的治疗提供理论依据。     

A role for copper in protozoan grazing – two billion years selecting for bacterial copper resistance

The Great Oxidation Event resulted in integration of soft metals in a wide range of biochemical processes including, in our opinion, killing of bacteria by protozoa. Compared to pressure from anthropologic copper contamination, little is known on impacts of protozoan predation on maintenance of copper resistance determinants in bacteria. To evaluate the role of copper and other soft metals in predatory mechanisms of protozoa, we examined survival of bacteria mutated in different transition metal efflux or uptake systems in the social amoeba Dictyostelium discoideum. Our data demonstrated a strong correlation between the presence of copper/zinc efflux as well as iron/manganese uptake, and bacterial survival in amoebae. The growth of protozoa, in turn, was dependent on bacterial copper sensitivity. The phagocytosis of bacteria induced upregulation of Dictyostelium genes encoding the copper uptake transporter p80 and a triad of Cu(I)‐translocating P_IB‐type ATPases. Accumulated Cu(I) in Dictyostelium was monitored using a copper biosensor bacterial strain. Altogether, our data demonstrate that Cu(I) is ultimately involved in protozoan predation of bacteria, supporting our hypothesis that protozoan grazing selected for the presence of copper resistance determinants for about two billion years.     

Metalloregulation of Gram-positive pathogen physiology

Owing to the unique redox potential of transition metals, many of these elements serve important roles as cofactors in numerous enzymes. However, the reactive nature of metal becomes an intracellular threat when these ions are present in excess. Therefore, all organisms require mechanisms for sensing small fluctuations in metal levels to maintain a controlled balance of uptake, efflux, and sequestration. The ability to sense metal ion concentration is especially important for the survival of pathogenic bacteria because host organisms can both restrict access to essential metals from invading pathogens and utilize the innate toxicity of certain metals for bacterial killing. Host-induced metal ion fluctuations must be rapidly sensed by pathogenic bacteria so that they can activate metal transport systems, alter their physiology to accommodate differences in metal concentrations, and regulate the expression of virulence factors.     

The IRT1 protein from Arabidopsis thaliana is a metal transporter with a broad substrate range

The molecular basis for the transport of manganese across membranes in plant cells is poorly understood. We have found that IRT1, an Arabidopsis thaliana metal ion transporter, can complement a mutant Saccharomyces cerevisiae strain defective in high-affinity manganese uptake (smf1). The IRT1 protein has previously been identified as an iron transporter. The current studies demonstrated that IRT1, when expressed in yeast, can transport manganese as well. This manganese uptake activity was inhibited by cadmium, iron(II) and zinc, suggesting that IRT1 can transport these metals. The IRT1 cDNA also complements a zinc uptake-deficient yeast mutant strain (zrt1zrt2), and IRT1-dependent zinc transport in yeast cells is inhibited by cadmium, copper, cobalt and iron(III). However, IRT1 did not complement a copper uptake-deficient yeast mutant (ctr1), implying that this transporter is not involved in the uptake of copper in plant cells. The expression of IRT1 is enhanced in A. thaliana plants grown under iron deficiency. Under these conditions, there were increased levels of root-associated manganese, zinc and cobalt, suggesting that, in addition to iron, IRT1 mediates uptake of these metals into plant cells. Taken together, these data indicate that the IRT1 protein is a broad-range metal ion transporter in plants.     

Copper in microbial pathogenesis: meddling with the metal

Transition metals such as iron, zinc, copper, and manganese are essential for the growth and development of organisms ranging from bacteria to mammals. Numerous studies have focused on the impact of iron availability during bacterial and fungal infections, and increasing evidence suggests that copper is also involved in microbial pathogenesis. Not only is copper an essential cofactor for specific microbial enzymes, but several recent studies also strongly suggest that copper is used to restrict pathogen growth in vivo. Here, we review evidence that animals use copper as an antimicrobial weapon and that, in turn, microbes have developed mechanisms to counteract the toxic effects of copper.     

Transporters of ligands for essential metal ions in plants

Essential metals are required for healthy plant growth but can be toxic when present in excess. Therefore plants have mechanisms of metal homeostasis which involve coordination of metal ion transporters for uptake, translocation and compartmentalization. However, very little metal in plants is thought to exist as free ions. A number of small, organic molecules have been implicated in metal ion homeostasis as metal ion ligands to facilitate uptake and transport of metal ions with low solubility and also as chelators implicated in sequestration for metal tolerance and storage. Ligands for a number of essential metals have been identified and proteins involved in the transport of these ligands and of metal-ligand complexes have been characterized. Here we review recent advances in understanding the role of mugineic acid, nicotianamine, organic acids (citrate and malate), histidine and phytate as ligands for iron (Fe), zinc (Zn), copper (Cu), manganese (Mn) and nickel (Ni) in plants, and the proteins identified as their transporters.     

Strength of Cu-efflux response in Escherichia coli coordinates metal resistance in Caenorhabditis elegans and contributes to the severity of environmental toxicity

Without effective homeostatic systems in place, excess copper (Cu) is universally toxic to organisms. While increased utilization of anthropogenic Cu in the environment has driven the diversification of Cu-resistance systems within enterobacteria, little research has focused on how this change in bacterial architecture impacts host organisms that need to maintain their own Cu homeostasis. Therefore, we utilized a simplified host–microbe system to determine whether the efficiency of one bacterial Cu-resistance system, increasing Cu-efflux capacity via the ubiquitous CusRS two-component system, contributes to the availability and subsequent toxicity of Cu in host Caenorhabditis elegans nematode. We found that a fully functional Cu-efflux system in bacteria increased the severity of Cu toxicity in host nematodes without increasing the C. elegans Cu-body burden. Instead, increased Cu toxicity in the host was associated with reduced expression of a protective metal stress-response gene, numr-1, in the posterior pharynx of nematodes where pharyngeal grinding breaks apart ingested bacteria before passing into the digestive tract. The spatial localization of numr-1 transgene activation and loss of bacterially dependent Cu-resistance in nematodes without an effective numr-1 response support the hypothesis that numr-1 is responsive to the bacterial Cu-efflux capacity. We propose that the bacterial Cu-efflux capacity acts as a robust spatial determinant for a host’s response to chronic Cu stress.     

Metal trafficking: from maintaining the metal homeostasis to future drug design

The diverse proteins and enzymes involved in metal trafficking between and inside human cells form numerous transport networks which are highly specific for each essential metal ion and apoprotein. Individual players include voltage-gated ion channels, import and export proteins, intracellular metal-ion sensors, storage proteins and chaperones. In the case of calcium, iron and copper, some of the most apparent trafficking avenues are now well established in eukaryotes, while others are just emerging (e.g. for zinc, manganese and molybdenum). Chemistry provides an important contribution to many issues surrounding these transport pathways, from metal binding-constants and ion specificity to metal-ion exchange kinetics. Ultimately, a better understanding of these processes opens up opportunities for metal-ion-related therapy, which goes beyond traditional chelate-based metal ion detoxification.     

Ion efflux systems involved in bacterial metal resistances

Summary Studying metal ion resistances gives us important insights into environmental processes and provides an understanding of basic living processes. This review concentrates on bacterial efflux systems for inorganic metal cations and anions, which have generally been found as resistance systems from bacteria isolated from metal-polluted environments. The protein products of the genes involved are sometimes prototypes of new families of proteins or of important new branches of known families. Sometimes, a group of related proteins (and presumedly the underlying physiological function) has still to be defined. For example, the efflux of the inorganic metal anion arsenite is mediated by a membrane protein which functions alone in Gram-positive bacteria, but which requires an additional ATPase subunit in some Gram-negative bacteria. Resistance to Cd²⁺ and Zn²⁺ in Gram-positive bacteria is the result of a P-type efflux ATPase which is related to the copper transport P-type ATPases of bacteria and humans (defective in the human hereditary diseases Menkes' syndrome and Wilson's disease). In contrast, resistance to Zn²⁺, Ni²⁺, Co²⁺ and Cd²⁺ in Gram-negative bacteria is based on the action of proton-cation antiporters, members of a newly-recognized protein family that has been implicated in diverse functions such as metal resistance/nodulation of legumes/cell division (therefore, the family is called RND). Another new protein family, named CDF for cation diffusion facilitator has as prototype the protein CzcD, which is a regulatory component of a cobalt-zinc-cadmium resistance determinant in the Gram-negative bacteriumAlcaligenes eutrophus. A family for the ChrA chromate resistance system in Gram-negative bacteria has still to be defined.     

The family of SMF metal ion transporters in yeast cells

Metal ions are vital for all organisms, and metal ion transporters play a crucial role in maintaining their homeostasis. The yeast (Saccharomyces cerevisiae) Smf transporters and their homologs in other organisms have a central role in the accumulation of metal ions and their distribution in different tissues and cellular organelles. In this work we generated null mutations in each individual SMF gene in yeast as well as in all combinations of the genes. Each null mutation exhibited sensitivity to metal ion chelators at different concentrations. The combination of null mutants DeltaSMF1 + DeltaSMF2 and the triple null mutant Delta3SMF failed to grow on medium buffered at pH 8 and 7.5, respectively. Addition of 5 microm copper or 25 microm manganese alleviated the growth arrest at the high pH or in the presence of the chelating agent. The transport of manganese was analyzed in the triple null mutant and in this mutant expressing each Smf protein. Although overexpression of Smf1p and Smf2p resulted in uptake that was higher than wild type cells, the expression of Smf3p gave no significant uptake above that of the triple mutant Delta3SMF. Western analysis with antibody against Smf3p indicated that this transporter does not reach the plasma membrane and may function at the Golgi or post-Golgi complexes. The iron uptake resulting from expression of Smf1p and Smf2p was analyzed in a mutant in which its iron transporters FET3 and FET4 were inactivated. Overexpression of Smf1p gave rise to a significant iron uptake that was sensitive to the sodium concentrations in the medium. We conclude that the Smf proteins play a major role in copper and manganese homeostasis and, under certain circumstances, Smf1p may function in iron transport into the cells.     

Transition metal homeostasis: from yeast to human disease

Transition metal ions are essential nutrients to all forms of life. Iron, copper, zinc, manganese, cobalt and nickel all have unique chemical and physical properties that make them attractive molecules for use in biological systems. Many of these same properties that allow these metals to provide essential biochemical activities and structural motifs to a multitude of proteins including enzymes and other cellular constituents also lead to a potential for cytotoxicity. Organisms have been required to evolve a number of systems for the efficient uptake, intracellular transport, protein loading and storage of metal ions to ensure that the needs of the cells can be met while minimizing the associated toxic effects. Disruptions in the cellular systems for handling transition metals are observed as a number of diseases ranging from hemochromatosis and anemias to neurodegenerative disorders including Alzheimer??s and Parkinson??s disease. The yeast Saccharomyces cerevisiae has proved useful as a model organism for the investigation of these processes and many of the genes and biological systems that function in yeast metal homeostasis are conserved throughout eukaryotes to humans. This review focuses on the biological roles of iron, copper, zinc, manganese, nickel and cobalt, the homeostatic mechanisms that function in S. cerevisiae and the human diseases in which these metals have been implicated.