Zinc Starvation Response in a Cyanobacterium Revealed
Zinc Starvation Response in a Cyanobacterium Revealed
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蓝藻中的锌饥饿反应被揭示
DOI：
10.1128/jb.00257-12
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发表时间：
2012
影响因子：
3.2
通讯作者：
D. Nies
中科院分区：
文献类型：
--
作者：
D. Nies
鱼腥藻需要多种金属用于其细胞生物化学。一般的问题是为正确的酶提供所有不同的金属，从而避免有毒的副作用和这些金属之间的干扰。鱼腥藻必须处理过剩的金属，但也与金属饥饿，这个问题必须解决许多环境，每个具有不同的金属阳离子的可用性。在这个问题上，Napolitano等人。（34）报告了一项研究，他们在研究中揭示了鱼腥藻的锌饥饿反应。锌是所有生物体中重要的必需微量元素。在大肠杆菌中已知超过100种锌依赖性或锌结合蛋白（39），例如，果糖二磷酸醛缩酶、DNA引发酶、碳酸酐酶、碱性磷酸酶和RNA聚合酶。在哺乳动物中，包括人类，锌是正常大脑功能以及胰岛素和精液释放所必需的，并作为细胞信号（30）。纳波利塔诺等人（34）讲述的故事读起来很精彩。他们确定了鱼腥藻、Zur和Zur控制下的数十个基因中科普锌缺乏的主要转录调节因子。其中最有趣的是假定的锌结合金属伴侣，其他调节蛋白，令人惊讶的是，TonB依赖性外膜蛋白，这可能涉及锌或锌螯合物跨外膜的主动运输。鱼腥藻甚至可能合成和分泌锌螯合剂（“锌载体”？），使人联想到用于铁的铁载体或用于铜获取的白垩载体。为了将这项工作（34）置于适当的背景下，重要的是要重申对鱼腥藻的了解，这种细菌如何生长，为什么它需要金属阳离子，在一般金属稳态的背景下锌稳态如何发挥作用，以及Napolitano等人的报告中的新内容。鱼腥藻PCC 7120是一种蓝细菌。如果没有这些生物，这个星球上的生命将是不同的。它们是细菌超王国的一个主要门，它们的生态位是生理位，即产氧光合作用。蓝细菌是唯一能够进行这种反应的生物体，无论是作为自由生活的生物体还是作为质体内共生体（或奴隶？）真核细胞。光合作用的产物是分子氧。当半电池电位（Eo=）为816 mV（61）时，在标准条件下（摩尔浓度; pH 7），电子从NADH（Eo= 320 mV）转移释放约238 kJ/mol，足以使每个转移的电子对保留3个ATP。没有其他呼吸电子受体允许这样高的能量守恒的电子转移依赖磷酸化。蓝藻分子氧的生产导致了两个主要的氧化事件约24亿和7亿年前，这可能引发了真核生物和多细胞生物的进化，分别（22，25，45）。因此，蓝藻有效地改变了我们星球的地球化学。鱼腥藻需要过渡金属来进行光合作用和固氮。含氧光合作用发生在类囊体中，类囊体是一种特殊的内部膜系统，包含光系统I和II。两者都含有叶绿素分子，在它们的中心有一个镁。一个含锰的水分解复合物连接到光系统II的电子转移后，光吸收从光系统II到质体醌。水分解复合物在其核心含有Mn 4CaO 5簇，在其附近有两个氯阴离子（59），将水氧化为分子氧，并将产生的电子一个接一个地提供给光系统II的中心。在随后的步骤中，电子从质体醌转移到含铁的细胞色素b6 f复合物，通过铜依赖性可溶性蛋白质质体蓝素转移到含铁的光系统I，并从这里，在被另一个光子推动后，转移到NADP。该过程还通过质子动力和F1 Fo ATP酶保存能量。最后，NADPH被用作氧化还原供体以通过卡尔文循环同化CO2。因此，含氧光合作用需要过渡金属锰、铁和铜，碱土金属镁和钙，以及卤素氯。固氮固氮酶复合物含有铁和钼。鱼腥藻菌株PCC 7120也可能能够合成替代的钒-铁依赖性固氮酶（NifH 2，all 1455）和钒依赖性氯过氧化物酶（alr 0672）。钴是钴胺素的一部分，镍是尿素酶和氢化酶的一部分，氢化酶是一种再吸收固氮酶产生的分子氢的酶，具有其他生理功能。如果我们沿着元素周期表从左到右移动第一个过渡期的元素，鱼腥藻有使用V，第二个过渡期的Mo（第一个过渡期的铬是作为硫酸盐拮抗剂的铬酸盐，非常有毒），Mn，Fe，Co，Ni，Cu，最后是Zn。因此，鱼腥藻对过渡金属和其他金属的需求令人印象深刻，并且像其他生物一样，必须解决将正确的金属转化为正确的蛋白质的问题。一般来说，大约40%的酶需要金属作为辅助因子，从Mg（16%）Zn（9%）Fe（8%）Mn（6%）Ca（2%）Co和Cu（1%）到K，Na，Ni，V，Mo，W，以及在一种情况下Cd（60）。过渡金属阳离子的金属分配问题特别困难，因为乍一看，第一过渡族（Mn，Fe，Co，Ni，Cu和Zn）的离子半径相似（图2）。在电池中，这些金属阳离子沿着Irving-Williams系列或“啄食顺序”（21）相互干扰，其中铜在顶部，锰在底部，对于产生分子氧至关重要，直到过渡
The cyanobacterium Anabaena needs a variety of metals for its cellular biochemistry. The general problem is to supply all the different metals to the right enzymes, thereby avoiding toxic side reactions and interference between these metals. Anabaena has to deal with surplus metals but also with metal starvation, and this problem has to be solved for many environments, each with a different availability of metal cations. In this issue, Napolitano et al. (34) report a study in which they unraveled the zinc starvation response in Anabaena. Zinc is an important essential trace element in all organisms. More than 100 zinc-dependent or -binding proteins are known in Escherichia coli (39), e.g., a fructose-bisphosphate aldolase, DNA primase, carbonic anhydrase, alkaline phosphatase, and RNA polymerase. In mammals, including humans, zinc is required for proper brain function and for insulin and semen release and acts as cellular signal (30). The story told by Napolitano et al. (34) is wonderful to read. They identified the main transcriptional regulator to cope with zinc deficiency in Anabaena, Zur, and dozens of genes under Zur control. Most interesting among those were putative zinc-binding metallochaperones, other regulatory proteins, and, surprisingly, TonB-dependent outer membrane proteins, which may be involved in active transport of zinc or zinc chelates across the outer membrane. Anabaena might even synthesize and excrete a zinc chelator (a “zincophore”?), reminiscent of siderophores for iron or chalkophores for copper acquisition. To place this work (34) in a proper context, it is important to reiterate what is known about Anabaena, how this bacterium grows, why it needs metal cations, how zinc homeostasis in the context of general metal homeostasis might function, and what is new in the report by Napolitano et al. (34) (Fig. 1). Anabaena sp. PCC 7120 is a cyanobacterium. Without these organisms, life on this planet would be different. They are a major phylum of the superkingdom Bacteria, and their ecological niche is a physiological one, namely, oxygenic photosynthesis. Cyanobacteria are the only organisms able to perform this reaction, either as free-living organisms or as plastid endosymbionts (or slaves?) of eukaryotic cells. The product of oxygenic photosynthesis is molecular oxygen. With a half-cell potential (Eo=) of 816 mV (61), transfer of electrons from NADH (Eo= 320 mV) releases about 238 kJ/mol under standard conditions (molar concentrations; pH 7), enough to conserve 3 ATP per electron pair transferred. No other respiratory electron acceptor allows such a high energy conservation by electron transfer-dependent phosphorylation. Production of molecular oxygen by cyanobacteria led to two major oxygenation events about 2.4 billion and 700 million years ago, which may have sparked evolution of eukaryotes and multicellular organisms, respectively (22, 25, 45). Thus, cyanobacteria have efficiently changed the biogeochemistry of our planet. Anabaena needs transition metals to perform oxygenic photosynthesis and for nitrogen fixation. Oxygenic photosynthesis occurs in thylakoids, a specialized internal membrane system that contains photosystems I and II. Both contain chlorophyll molecules, which harbor a Mg at their center. A Mn-containing water-splitting complex attached to photosystem II replenishes electrons that are transferred after light absorption from photosystem II to a plastoquinone. The water-splitting complex contains at its core a Mn4CaO5 cluster with two chloride anions in its vicinity (59), oxidizes water to molecular oxygen, and donates the resulting electrons one by one to the center of photosystem II. In the subsequent steps, electrons are transferred from the plastoquinone to an iron-containing cytochrome b6f complex, via the copper-dependent soluble protein plastocyanin to the iron-containing photosystem I, and from here, after being pushed by another photon, to NADP . This process also conserves energy via the proton motive force and the F1Fo ATPase. Finally, NADPH is used as a redox donor to assimilate CO2 via the Calvin cycle. Oxygenic photosynthesis, therefore, needs the transition metals manganese, iron, and copper, the earth alkali metals magnesium and calcium, and the halogen chlorine. The nitrogen-fixing nitrogenase complex contains iron and molybdenum. Anabaena sp. strain PCC 7120 may also be able to synthesize an alternative vanadium-iron-dependent nitrogenase (NifH2, all1455) and a vanadium-dependent chloroperoxidase (alr0672). Cobalt is part of the component cobalamin, and nickel is part of urease and of hydrogenase, an enzyme that reassimilates molecular hydrogen produced by the nitrogenases among other physiological functions. If we move along the periodic table of the elements in the first transition period from left to right, Anabaena has use for V, Mo of the second transition period (chromium of the first period is as chromate a sulfate antagonist and very toxic), Mn, Fe, Co, Ni, Cu, and finally Zn. Thus, Anabaena has an impressive need for transition and other metals and, like other organisms, must solve the problem of getting the correct metal to the right protein. In general, about 40% of all enzymes need metals as cofactors, ranking from Mg (16%) Zn (9%) Fe (8%) Mn (6%) Ca (2%) Co and Cu (1%) down to K, Na, Ni, V, Mo, W, and in one case Cd (60). The problem of metal allocation is especially difficult for transition metal cations because, at first glance, those of the first transition group (Mn, Fe, Co, Ni, Cu, and Zn) have similar ionic radii (Fig. 2). In the cell, these metal cations interfere with each other along the Irving-Williams series or “pecking order” (21), which has copper on top and manganese, essential for production of molecular oxygen, at the bottom as far as transition
DOI：
10.1073/pnas.97.2.652
发表时间：
2000-01-18
影响因子：
11.1
作者：
Rensing, C;Fan, B;Rosen, BP
通讯作者：
Rosen, BP
DOI：
10.1073/pnas.94.26.14326
发表时间：
1997-12-23
影响因子：
11.1
作者：
Rensing, C;Mitra, B;Rosen, BP
通讯作者：
Rosen, BP
影响因子：
2.1
作者：
Lee, SM;Grass, G;Rensing, C
通讯作者：
Rensing, C