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Lookup NU author(s): Dr Dr MD Harrison Harrison, Andrea Robinson, Dr Jennifer Cavet, Professor Nigel Robinson
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Zinc is essential for many cellular processes, including DNA synthesis, transcription, and translation, but excess can be toxic. A zinc-induced gene, smtA, is required for normal zinc-tolerance in the cyanobacterium Synechococcus PCC 7942. Here we report that the protein SmtA contains a cleft lined with Cys-sulfur and His-imidazole ligands that binds four zinc ions in a Zn4Cys9His2 cluster. The thiolate sulfurs of five Cys ligands provide bridges between the two ZnCys4 and two ZnCys3His sites, giving two fused six-membered rings with distorted boat conformations. The inorganic core strongly resembles the Zn4Cys11 cluster of mammalian metallothionein, despite different amino acid sequences, a different linear order of the ligands, and presence of histidine ligands. Also, SmtA contains elements of secondary structure not found in metallothioneins. One of the two Cys4-coordinated zinc ions in SmtA readily exchanges with exogenous metal (111Cd), whereas the other is inert. The thiolate sulfur ligands bound to zinc in this site are buried within the protein. Regions of β-strand and α-helix surround the inert site to form a zinc finger resembling the zinc fingers in GATA and LIM-domain proteins. Eukaryotic zinc fingers interact specifically with other proteins or DNA and an analogous interaction can therefore be anticipated for prokaryotic zinc fingers. SmtA now provides structural proof for the existence of zinc fingers in prokaryotes, and sequences related to the zinc finger motif can be identified in several bacterial genomes.
Author(s): Harrison MD; Robinson AK; Robinson NJ; Cavet JS; Blindauer CA; Parkinson JA; Sadler PJ
Publication type: Article
Publication status: Published
Journal: Proceedings of the National Academy of Sciences of the United States of America
Year: 2001
Volume: 98
Issue: 17
Pages: 9593-9598
ISSN (print): 0027-8424
ISSN (electronic): 1091-6490
Publisher: National Academy of Sciences
URL: http://dx.doi.org/10.1073/pnas.171120098
DOI: 10.1073/pnas.171120098
PubMed id: 11493688
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