van Vliet Arnoud H M, Stoof Jeroen, Poppelaars Sophie W, Bereswill Stefan, Homuth Georg, Kist Manfred, Kuipers Ernst J, Kusters Johannes G
Department of Gastroenterology and Hepatology, Erasmus MC University Medical Center Rotterdam, 3015 GD Rotterdam, The Netherlands.
J Biol Chem. 2003 Mar 14;278(11):9052-7. doi: 10.1074/jbc.M207542200. Epub 2002 Dec 23.
The production of high levels of ammonia allows the human gastric pathogen Helicobacter pylori to survive the acidic conditions in the human stomach. H. pylori produces ammonia through urease-mediated degradation of urea, but it is also able to convert a range of amide substrates into ammonia via its AmiE amidase and AmiF formamidase enzymes. Here data are provided that demonstrate that the iron-responsive regulatory protein Fur directly and indirectly regulates the activity of the two H. pylori amidases. In contrast to other amidase-positive bacteria, amidase and formamidase enzyme activities were not induced by medium supplementation with their respective substrates, acrylamide and formamide. AmiE protein expression and amidase enzyme activity were iron-repressed in H. pylori 26695 but constitutive in the isogenic fur mutant. This regulation was mediated at the transcriptional level via the binding of Fur to the amiE promoter region. In contrast, formamidase enzyme activity was not iron-repressed but was significantly higher in the fur mutant. This effect was not mediated at the transcriptional level, and Fur did not bind to the amiF promoter region. These roles of Fur in regulation of the H. pylori amidases suggest that the H. pylori Fur regulator may have acquired extra functions to compensate for the absence of other regulatory systems.
高水平氨的产生使人类胃部病原体幽门螺杆菌能够在人类胃部的酸性环境中存活。幽门螺杆菌通过脲酶介导的尿素降解产生氨，但它也能够通过其AmiE酰胺酶和AmiF甲酰胺酶将一系列酰胺底物转化为氨。本文提供的数据表明，铁反应调节蛋白Fur直接和间接调节两种幽门螺杆菌酰胺酶的活性。与其他酰胺酶阳性细菌不同，补充各自底物丙烯酰胺和甲酰胺的培养基并未诱导酰胺酶和甲酰胺酶的活性。在幽门螺杆菌26695中，AmiE蛋白表达和酰胺酶活性受铁抑制，但在同基因fur突变体中则为组成型。这种调节是通过Fur与amiE启动子区域的结合在转录水平上介导的。相反，甲酰胺酶活性不受铁抑制，但在fur突变体中显著更高。这种效应不是在转录水平上介导的，并且Fur不与amiF启动子区域结合。Fur在调节幽门螺杆菌酰胺酶中的这些作用表明，幽门螺杆菌Fur调节因子可能获得了额外的功能，以补偿其他调节系统的缺失。
