Schauer Kristine, Gouget Barbara, Carrière Marie, Labigne Agnès, de Reuse Hilde
Unité de Pathogénie Bactérienne des Muqueuses, Département de Microbiologie, Institut Pasteur, 75724 Paris Cedex 15, France.
Mol Microbiol. 2007 Feb;63(4):1054-68. doi: 10.1111/j.1365-2958.2006.05578.x.
Nickel is a cofactor for various microbial enzymes, yet as a trace element, its scavenging is challenging. In the case of the pathogen Helicobacter pylori, nickel is essential for the survival in the human stomach, because it is the cofactor of the important virulence factor urease. While nickel transport across the cytoplasmic membrane is accomplished by the nickel permease NixA, the mechanism by which nickel traverses the outer membrane (OM) of this Gram-negative bacterium is unknown. Import of iron-siderophores and cobalamin through the bacterial OM is carried out by specific receptors energized by the TonB/ExbB/ExbD machinery. In this study, we show for the first time that H. pylori utilizes TonB/ExbB/ExbD for nickel uptake in addition to iron acquisition. We have identified the nickel-regulated protein FrpB4, homologous to TonB-dependent proteins, as an OM receptor involved in nickel uptake. We demonstrate that ExbB/ExbD/TonB and FrpB4 deficient bacteria are unable to efficiently scavenge nickel at low pH. This condition mimics those encountered by H. pylori during stomach colonization, under which nickel supply and full urease activity are essential to combat acidity. We anticipate that this nickel scavenging system is not restricted to H. pylori, but will be represented more largely among Gram-negative bacteria.
镍是多种微生物酶的辅助因子，但作为一种微量元素，其清除具有挑战性。就病原体幽门螺杆菌而言，镍对其在人类胃部的存活至关重要，因为它是重要毒力因子脲酶的辅助因子。虽然镍通过细胞质膜的转运是由镍通透酶NixA完成的，但镍穿过这种革兰氏阴性菌外膜（OM）的机制尚不清楚。铁载体和钴胺素通过细菌外膜的导入是由TonB/ExbB/ExbD机制提供能量的特定受体来进行的。在本研究中，我们首次表明幽门螺杆菌除了获取铁之外，还利用TonB/ExbB/ExbD来摄取镍。我们已鉴定出与TonB依赖性蛋白同源的镍调节蛋白FrpB4，它是一种参与镍摄取的外膜受体。我们证明，ExbB/ExbD/TonB和FrpB4缺陷型细菌在低pH值下无法有效清除镍。这种情况模拟了幽门螺杆菌在胃部定殖过程中遇到的情况，在此情况下，镍供应和完整的脲酶活性对于抵抗酸性至关重要。我们预计这种镍清除系统不仅限于幽门螺杆菌，而是在革兰氏阴性菌中更为普遍。
