How do bacterial cells ensure that metalloproteins get the correct metal?

Abstract

Protein metal-coordination sites are richly varied and exquisitely attuned to their inorganic partners, yet many metalloproteins still select the wrong metals when presented with mixtures of elements. Cells have evolved elaborate mechanisms to scavenge for sufficient metal atoms to meet their needs and to adjust their needs to match supply. Metal sensors, transporters and stores have often been discovered as metal-resistance determinants, but it is emerging that they perform a broader role in microbial physiology: they allow cells to overcome inadequate protein metal affinities to populate large numbers of metalloproteins with the right metals.

Metal Selectivity of the Escherichia coli Nickel Metallochaperone, SlyD

“…This result raises the question as to how SlyD in vivo is able to overcome the preference for Zn(II) over Ni(II). One possible explanation involves metal-induced allostery (2,41). In this event, the binding of the "correct metal" is exploited to drive changes in the secondary/tertiary/quaternary structure of the protein and/or dynamics (i.e.…”

“…The following metal salts, ZnSO 4 , [Cu(CH 3 CN) 4 ]PF 6 , Ni(acetate) 2 , CoSO 4 , FeSO 4 and MnCl 2 were purchased from Aldrich as a minimum 99.9% pure. Except for copper, all metal solutions were prepared by dissolving the salts as purchased in Milli-Q water that was stirred in an anaerobic glovebox (O 2 < 1 ppm) for at least 24 h to minimize oxygen content.…”

“…The proteins involved in metal homeostasis include membrane importers/ exporters, metal storage proteins that are responsible for safe sequestration, metallochaperones dedicated to targeted delivery of metal ions, as well as metal-sensing transcription factors, which together control the amount of a specific metal available in the cellular cytoplasm. The fidelity of these proteins is at the top of a hierarchy of metalselective processes, and their selectivity is proposed to ultimately influence the metal occupancy of all other proteins that require a metal ion cofactor for function (2,3). Therefore, a detailed understanding of the proteins involved in metal homeostasis and their ability to recognize and chelate a cognate metal partner is a prerequisite for deciphering how metal selectivity is achieved in the context of an entire cell.…”

“…Metal homeostasis is an essential yet complex process that is achieved through the action of a number of proteins often working in concert (1,2). These factors ensure that metaldependent proteins are paired with the correct metal ion(s) to produce biologically active complexes.…”

Fate of Trace Metals in Anaerobic Digestion

“…A well-studied example is microbial Fe acquisition by excretion of Fe-chelating siderophores and further uptake by cognate receptors [50]. Similar processes are believed to be responsible for the increase in Co and Ni solubility and bio-uptake under sulfidic conditions of the natural environments [51,52]. Some microorganisms have developed metal efflux mechanisms, which pumps excess intracellular metals out of the cell as a strategy against metal toxicity when exposed to high concentrations of metals [53].…”