Multiple bacteria encode metallothioneins and SmtA-like zinc fingers.
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.
Department of Chemistry, University of Edinburgh, Edinburgh EH9 3JJ, Scotland, UK.
Claudia A
CA
Blindauer
Mark D
MD
Harrison
Andrea K
AK
Robinson
John A
JA
Parkinson
Peter W
PW
Bowness
Peter J
PJ
Sadler
Nigel J
NJ
Robinson
D000595:Amino Acid Sequence; D017033:Anabaena / Q000235:genetics / Q000378:metabolism; D001419:Bacteria / Q000235:genetics* / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D001665:Binding Sites; D003545:Cysteine / Q000737:chemistry; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005798:Genes, Bacterial; D006863:Hydrogen-Ion Concentration; D008668:Metallothionein / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D011550:Pseudomonas aeruginosa / Q000235:genetics / Q000378:metabolism; D016958:Pseudomonas putida / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015032:Zinc / Q000378:metabolism; D016335:Zinc Fingers / Q000235:genetics*
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; C080048:smtA protein, Synechococcus; D008668:Metallothionein; D015032:Zinc; D003545:Cysteine