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Severe zinc depletion of escherichia coli: roles for high affinity zinc binding by ZinT, zinc transport and zinc-independent proteins \ud \ud \ud \ud

By A.I. Graham, S. Hunt, S.L. Stokes, N. Bramall, J. Bunch, A.G. Cox, C.W. McLeod and R.K. Poole

Abstract

Zinc ions play indispensable roles in biological chemistry. However, bacteria have an impressive ability to acquire Zn2+ from the environment, making it exceptionally difficult to achieve Zn2+ deficiency, and so a comprehensive understanding of the importance of Zn2+ has not been attained. Reduction of the Zn2+ 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 Zn2+-deficient medium had a reduced growth rate and contained up to five times less cellular Zn2+. To understand global responses to Zn2+ deficiency, microarray analysis was conducted of cells grown under Zn2+-replete and Zn2+-depleted conditions in chemostat cultures. Nine genes were up-regulated more than 2-fold (p<0.05) in cells from Zn2+-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 Zn2+ level under Zn2+ limitation. The purified ZinT protein possessed a single, high affinity metal-binding site that can accommodate Zn2+ or Cd2+. A further up-regulated gene, ykgM, is believed to encode a non-Zn2+ finger-containing paralogue of the Zn2+ finger ribosomal protein L31. The gene encoding the periplasmic Zn2+- binding protein znuA showed increased expression. During both batch and chemostat growth, cells "found" more Zn2+ than was originally added to the culture, presumably because of leaching from the culture vessel. Zn2+ elimination is shown to be a more precise method of depleting Zn2+ than by using the chelator N,N,N',N'-tetrakis(2-pyridylmethyl)ethylenediamine

Publisher: American Society for Biochemistry and Molecular Biology
Year: 2009
OAI identifier: oai:eprints.whiterose.ac.uk:9031

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