de Castro Ferreira Ivan Gonçalves, Rodrigues Mirian Molnar, da Silva Neto José Freire, Mazzon Ricardo Ruiz, do Valle Marques Marilis
Departamento de Microbiologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, Av. Prof. Lineu Prestes 1374, São Paulo, SP, 05508-900, Brazil.
Departamento de Biologia Celular e Molecular e Bioagentes Patogênicos, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Av. Bandeirantes, 3900, Ribeirão Preto, SP, 14049-900, Brazil.
Biometals. 2016 Oct;29(5):851-62. doi: 10.1007/s10534-016-9956-y. Epub 2016 Aug 2.
Iron is an essential nutrient that is poorly available to living organisms but can be harmful when in excess due to the production of reactive oxygen species. Bacteria and other organisms use iron storage proteins called ferritins to avoid iron toxicity and as a safe iron source in the cytosol. The alpha-proteobacterium Caulobacter crescentus has two putative ferritins, Bfr and Dps, and some other proteins belonging to the ferritin-like superfamily, among them the one encoded by CC_0557. In this work, we have analyzed the role and regulation of these three putative ferritin-like proteins. Using lacZ-transcriptional fusions, we found that bfr expression is positively regulated (2.5-fold induction) by the Fe-responsive regulator Fur in iron sufficiency, as expected for an iron storage protein. Expression of dps was induced 1.5-fold in iron limitation in a Fur-independent manner, while the expression of the product of CC_0557 was unaffected by either iron supply or Fur. With respect to growth phase, while bfr expression was constant during growth, expression of dps (1.4-fold) and CC_0557 (around seven times) increased in the transition from exponential to stationary phase. Deletion mutant strains for each gene and a double dps/bfr mutant were obtained and tested for oxidative stress resistance. The dps mutant was very sensitive to H2O2, and this phenotype was not relieved by the addition of the iron chelator 2',2-dipyridyl in the conditions tested. While bfr and CC_0557 showed no phenotype as to H2O2 resistance, the double dps/bfr mutant had a similar phenotype to the dps mutation alone. These findings indicate that in C. crescentus Bfr contributes to iron homeostasis and Dps has a role in protection against oxidative stress. The role of the protein CC_0557 containing a ferritin-like fold remains unclear.
铁是一种对生物体至关重要的营养素，但生物体难以获取，且过量时会因活性氧的产生而有害。细菌和其他生物利用称为铁蛋白的铁储存蛋白来避免铁毒性，并作为细胞质中安全的铁源。α-变形菌新月柄杆菌有两种假定的铁蛋白，即Bfr和Dps，以及一些属于铁蛋白样超家族的其他蛋白质，其中包括由CC_0557编码的蛋白质。在这项工作中，我们分析了这三种假定的铁蛋白样蛋白质的作用和调控。使用lacZ转录融合，我们发现bfr的表达在铁充足时受到铁响应调节因子Fur的正向调控（诱导2.5倍），这对于铁储存蛋白来说是预期的。dps的表达在铁限制条件下以不依赖Fur的方式诱导1.5倍，而CC_0557产物的表达不受铁供应或Fur的影响。关于生长阶段，虽然bfr的表达在生长过程中保持恒定，但dps（1.4倍）和CC_0557（约7倍）的表达在从指数生长期到稳定期的转变中增加。获得了每个基因的缺失突变株以及双dps/bfr突变株，并测试了它们对氧化应激的抗性。dps突变株对H2O2非常敏感，在测试条件下添加铁螯合剂2',2-联吡啶并不能缓解这种表型。虽然bfr和CC_0557在H2O2抗性方面没有表现出表型，但双dps/bfr突变株具有与单独的dps突变相似的表型。这些发现表明，在新月柄杆菌中，Bfr有助于铁稳态，而Dps在抗氧化应激中发挥作用。含有铁蛋白样折叠的CC_0557蛋白的作用仍不清楚。
