Nickel Metallomics: General Themes Guiding Nickel Homeostasis

Abstract

The nickel metallome describes the distribution and speciation of nickel within the cells of organisms that utilize this element. This distribution is a consequence of nickel homeostasis, which includes import, storage, and export of nickel, incorporation into metalloenzymes, and the modulation of these and associated cellular systems through nickel-regulated transcription. In this chapter, we review the current knowledge of the most common nickel proteins in prokaryotic organisms with a focus on their coordination environments. Several underlying themes emerge upon review of these nickel systems, which illustrate the common principles applied by nature to shape the nickel metallome of the cell.

UreE-UreG Complex Facilitates Nickel Transfer and Preactivates GTPase of UreG in Helicobacter pylori

“…The utilization of nickel must be tightly controlled in H. pylori as a plethora of nickel causes serious cell damage to H. pylori (9). Therefore, H. pylori has developed an elaborate system to tightly regulate the cellular nickel homeostasis from uptake, storage, and delivery to efflux through biosynthesis of a series of metalloproteins and chaperones (10), such as nickel storage protein Hpn and Hpnl (11)(12)(13)(14), which are only produced by this pathogen, and HspA (15,16), which has a distinct His-Cys-rich C terminus with nickel binding ability.…”

Nickel recognition by bacterial importer proteins

“…34 In this case, CeuE His 103 displaces one His imidazole Nδ. The LHis ligand atoms are in the all cis configuration, and the bound complex is virtually identical in structure to the fivecoordinate free Cu(II)-(L-His) 2 complex. 26 The completion of the coordination sphere by His 103 exemplifies the manner in which a protein His residue could be used to discriminate metals (divalent Ni versus divalent Cu) based on coordination number, if not stereoisomer preference.…”

“…L-histidine is present in the intestine in amounts consistent with its role in E. coli nickel-uptake. 18 A structure of the complex Ni-(L-His) 2 :NikA followed shortly thereafter. 19 In addition to confirming the experimentally determined stoichiometry, several interesting features of Ni-recognition were revealed.…”

“…21 However, when the similar Co(II)-(His) 2 was oxidized to the exchange inert Co(III) complex, three isomers were isolated (trans-COO -, trans-NH 2 , and trans-imidazole) in a non-equivalent ratio, albeit strongly favouring trans-imidazole. [22][23][24] The Ni-(LHis) 2 …”

“…Terrestrial and marine microbes can require nickel to metabolize urea in the soil, generate methane, produce H 2 to get rid of excess reducing equivalents from photosynthesis, or to defend against reactive oxygen species. The proteins required for Nienzyme assembly and Ni-homeostasis are also well studied, 2 with a particular focus on their metal coordination properties. 3,4 This latter aspect is important for understanding metal selective function, but also bears on mechanisms of metal transfer reactions, an emerging area of research activity for Ni-assembly proteins.…”