Graham, AI, Hunt, S, Stokes, SL, Bramall, N, Bunch, J, Cox, AG, McLeod, CW and Poole, RK (2009) Severe zinc depletion of Escherichia coli: roles for high affinity zinc binding by ZinT, zinc transport and zinc-independent proteins. J. Biol. Chem. 284:18377-89
Zinc ions play indispensable roles in biological chemistry. However, bacteria have an impressive ability to acquire Zn(2+) from the environment, making it exceptionally difficult to achieve Zn(2+) deficiency, and so a comprehensive understanding of the importance of Zn(2+) has not been attained. Reduction of the Zn(2+) content of Escherichia coli growth medium to 60 nm or less is reported here for the first time, without recourse to chelators of poor specificity. Cells grown in Zn(2+)-deficient medium had a reduced growth rate and contained up to five times less cellular Zn(2+). To understand global responses to Zn(2+) deficiency, microarray analysis was conducted of cells grown under Zn(2+)-replete and Zn(2+)-depleted conditions in chemostat cultures. Nine genes were up-regulated more than 2-fold (p < 0.05) in cells from Zn(2+)-deficient chemostats, including zinT (yodA). zinT is shown to be regulated by Zur (zinc uptake regulator). A mutant lacking zinT displayed a growth defect and a 3-fold lowered cellular Zn(2+) level under Zn(2+) limitation. The purified ZinT protein possessed a single, high affinity metal-binding site that can accommodate Zn(2+) or Cd(2+). A further up-regulated gene, ykgM, is believed to encode a non-Zn(2+) finger-containing paralogue of the Zn(2+) finger ribosomal protein L31. The gene encoding the periplasmic Zn(2+)-binding protein znuA showed increased expression. During both batch and chemostat growth, cells "found" more Zn(2+) than was originally added to the culture, presumably because of leaching from the culture vessel. Zn(2+) elimination is shown to be a more precise method of depleting Zn(2+) than by using the chelator N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine.
Binding Sites; Binding, Competitive/physiology; Biological Transport/physiology; Escherichia coli/genetics; Escherichia coli/growth & development; Escherichia coli/metabolism; Escherichia coli Proteins/chemistry; Escherichia coli Proteins/genetics; Escherichia coli Proteins/metabolism; Fluorescent Dyes/metabolism; Fura-2/analogs & derivatives; Fura-2/metabolism; Gene Expression Profiling; Gene Expression Regulation, Bacterial/physiology; Microbiological Techniques; Oligonucleotide Array Sequence Analysis; Protein Structure, Tertiary; Ribosomal Proteins/chemistry; Ribosomal Proteins/genetics; Ribosomal Proteins/metabolism; Zinc/deficiency; Zinc/metabolism
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