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Protein-folding location can regulate manganese-binding versus copper- or zinc-binding

Lookup NU author(s): Dr Stephen Tottey, Dr Kevin Waldron, Dr Susan Firbank, Dr Katsuko Sato, Dr Timothy Cheek, Dr Joseph Gray, Dr Mark Banfield, Professor Christopher Dennison, Professor Nigel Robinson

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Abstract

Metals are needed by at least one-quarter of all proteins(1,2). Although metallochaperones(3-8) insert the correct metal into some proteins, they have not been found for the vast majority, and the view is that most metalloproteins acquire their metals directly from cellular pools. However, some metals form more stable complexes with proteins than do others. For instance, as described in the Irving Williams series(9), Cu2+ and Zn2+ typically form more stable complexes than Mn2+. Thus it is unclear what cellular mechanisms manage metal acquisition by most nascent proteins. To investigate this question, we identified the most abundant Cu2+-protein, CucA (Cu2+- cupin A), and the most abundant Mn2+- protein, MncA (Mn2+- cupin A), in the periplasm of the cyanobacterium Synechocystis PCC 6803. Each of these newly identified proteins binds its respective metal via identical ligands within a cupin fold. Consistent with the Irving - Williams series, MncA only binds Mn2+ after folding in solutions containing at least a 10(4) times molar excess of Mn2+ over Cu2+ or Zn2+. However once MncA has bound Mn2+, the metal does not exchange with Cu2+. MncA and CucA have signal peptides for different export pathways into the periplasm, Tat and Sec respectively. Export by the Tat pathway allows MncA to fold in the cytoplasm, which contains only tightly bound copper or Zn2+ ( refs 10-12) but micromolar Mn2+ ( ref. 13). In contrast, CucA folds in the periplasm to acquire Cu2+. These results reveal a mechanism whereby the compartment in which a protein folds overrides its binding preference to control its metal content. They explain why the cytoplasm must contain only tightly bound and buffered copper and Zn2+.


Publication metadata

Author(s): Tottey S, Waldron KJ, Firbank SJ, Reale B, Bessant C, Sato K, Cheek TR, Gray J, Banfield MJ, Dennison C, Robinson NJ

Publication type: Article

Publication status: Published

Journal: Nature

Year: 2008

Volume: 455

Issue: 7216

Pages: 1138-1142

ISSN (print): 0028-0836

ISSN (electronic): 1476-4687

Publisher: Nature Publishing Group

URL: http://dx.doi.org/10.1038/nature07340

DOI: 10.1038/nature07340


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