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Multiple bacteria encode metallothioneins and SmtA‐like zinc fingers
Author(s) -
Blindauer Claudia A.,
Harrison Mark D.,
Robinson Andrea K.,
Parkinson John A.,
Bowness Peter W.,
Sadler Peter J.,
Robinson Nigel J.
Publication year - 2002
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.2002.03109.x
Subject(s) - metallothionein , zinc , cysteine , escherichia coli , anabaena , biology , zinc finger , biochemistry , pseudomonas putida , zinc finger nuclease , histidine , bacteria , amino acid , cyanobacteria , chemistry , gene , transcription factor , genetics , organic chemistry , enzyme
Summary Zinc is essential but toxic in excess. Bacterial metallothionein, SmtA from Synechococcus PCC 7942, sequesters and detoxifies four zinc ions per molecule and contains a zinc finger structurally similar to eukaryotic GATA. The dearth of other reported bacterial metallothioneins has been surprising. Here we describe related bacterial metallothioneins (BmtA) from Anabaena PCC 7120, Pseudomonas aeruginosa and Pseudomonas putida that bind multiple zinc ions with high stability towards protons. Thiol modification demonstrates that cysteine coordinates zinc in all of these proteins. Additionally, 111 Cd‐NMR, and 111 Cd‐edited 1 H‐NMR, identified histidine ligands in Anabaena PCC 7120 BmtA, analogous to SmtA. A related Escherichia coli protein bound only a single zinc ion, via four cysteine residues, with low stability towards protons; 111 Cd‐NMR and 111 Cd‐edited 1 H‐NMR confirmed exclusive cysteine‐coordination, and these cysteine residues reacted rapidly with 5,5′‐dithiobis‐(2‐nitrobenzoic acid). 1 H‐NMR of proteins from P. aeruginosa , Anabaena PCC 7120 and E. coli generated fingerprints diagnostic for the GATA‐like zinc finger fold of SmtA. These studies reveal first the existence of multiple bacterial metallothioneins, and second proteins with SmtA‐like lone zinc fingers, devoid of a cluster, and designated GatA. We have identified 12 smtA ‐like genes in sequence databases including four of the gatA type.