Nickel homeostasis in Escherichia coli -: the rcnR-rcnA efflux pathway and its linkage to NikR function
Nickel homeostasis in Escherichia coli -: the rcnR-rcnA efflux pathway and its linkage to NikR function
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DOI：
10.1111/j.1365-2958.2006.05369.x
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发表时间：
2006-10-01
影响因子：
3.6
通讯作者：
Chivers, Peter T.
中科院分区：
文献类型：
--
作者：
Iwig, Jeffrey S.;Rowe, Jessica L.;Chivers, Peter T.
大肠杆菌的镍生理主要由其在厌氧生长条件下表达的镍铁氢酶同工酶控制。在大肠杆菌中的氢酶活性需要NikABCDE镍转运蛋白，在过量镍存在的情况下，该转运蛋白被NikR转录抑制。最近，在大肠杆菌中发现了一种镍钴外排蛋白RcnA。这项研究考察了RcnA对大肠杆菌中镍稳态的影响。在镍限制条件下，缺失rcnA会增加体内NikR的活性。依赖镍和钴的rcnA表达调节需要新发现的转录抑制因子RcnR(以前的Yohl)。RcnR的缺失会导致结构性的rcnA表达和相应的NikR活性降低。纯化的RcnR与RcnA启动子DNA片段直接结合，这种相互作用被镍和钴抑制。镍的积累在镍稳态受损的缺失菌株中受到不同的影响。令人惊讶的是，在低镍增长条件下，通过NikABCDE进口镍需要rcnA表达。这些数据支持了一个在大肠杆菌中有两个不同镍离子池的模型。NikR通过根据第二个池中的镍水平控制氢酶相关池的水平来连接这两个池。
The nickel physiology of Escherichia coli is dominated by its Ni-Fe hydrogenase isozymes, which are expressed under anaerobic growth conditions. Hydrogenase activity in E. coli requires the NikABCDE nickel transporter, which is transcriptionally repressed by NikR in the presence of excess nickel. Recently, a nickel and cobalt-efflux protein, RcnA, was identified in E. coli. This study examines the effect of RcnA on nickel homeostasis in E. coli. Under nickel-limiting conditions, deletion of rcnA increased NikR activity in vivo. Nickel and cobalt-dependent regulation of rcnA expression required the newly identified transcriptional repressor RcnR (formerly YohL). Deletion of rcnR results in constitutive rcnA expression and a corresponding decrease in NikR activity. Purified RcnR binds directly to the rcnA promoter DNA fragment and this interaction is inhibited by nickel and cobalt. Nickel accumulation is affected differently among deletion strains with impaired nickel homeostasis. Surprisingly, in low nickel growth conditions rcnA expression is required for nickel import via NikABCDE. The data support a model with two distinct pools of nickel ions in E. coli. NikR bridges these two pools by controlling the levels of the hydrogenase-associated pool based on the nickel levels in the second pool.