1jjd
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(New page: 200px<br /><applet load="1jjd" size="450" color="white" frame="true" align="right" spinBox="true" caption="1jjd" /> '''NMR structure of the Cyanobacterial Metallot...)
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Revision as of 16:12, 20 November 2007
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NMR structure of the Cyanobacterial Metallothionein SmtA
Overview
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 Zn(4)Cys(9)His(2) cluster. The thiolate sulfurs of five Cys, ligands provide bridges between the two ZnCys(4) and two ZnCys(3)His, sites, giving two fused six-membered rings with distorted boat, conformations. The inorganic core strongly resembles the Zn(4)Cys(11), 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 Cys(4)-coordinated zinc ions in, SmtA readily exchanges with exogenous metal ((111)Cd), whereas the other, is inert. The thiolate sulfur ligands bound to zinc in this site are, buried within the protein. Regions of beta-strand and alpha-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.
About this Structure
1JJD is a Single protein structure of sequence from Synechococcus sp. with ZN as ligand. Full crystallographic information is available from OCA.
Reference
A metallothionein containing a zinc finger within a four-metal cluster protects a bacterium from zinc toxicity., Blindauer CA, Harrison MD, Parkinson JA, Robinson AK, Cavet JS, Robinson NJ, Sadler PJ, Proc Natl Acad Sci U S A. 2001 Aug 14;98(17):9593-8. Epub 2001 Aug 7. PMID:11493688
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