Team:Cornell/project/background/metallothionein

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<h2 style="margin-top: 0px;">What are they?</h2>
<h2 style="margin-top: 0px;">What are they?</h2>
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Metallothioneins are a group of low-molecular-weight proteins that rapidly bind with divalent metal ions.<sup>[1]</sup>  Metallothioneins exist in almost every living organism and have many functions ranging from the control of oxidative stress to the regulation of redox potentials to the protection against toxic heavy metals.<sup>[1]</sup> For our project, we will take advantage of this final function where our recombinantly expressed metallothioneins will permanently sequester metals intracellularly while simultaneously providing resistance to engineered cells.  
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Metallothioneins are a group of low-molecular-weight proteins that rapidly bind with divalent metal ions.<sup>[1]</sup>  Metallothioneins exist in almost every living organism and have many functions ranging from control of oxidative stress, regulation of redox potentials, and protection against toxic heavy metals.<sup>[1]</sup> For our project we will take advantage of this final function where our recombinantly expressed metallothioneins will permanently sequester metals intracellularly while simultaneously providing resistance to engineered cells.  
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<h2>Mode of binding</h2>
<h2>Mode of binding</h2>
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Metallothionein proteins across species have highly conserved sequences with approximately 30% of all residues as cysteines.<sup>[2]</sup>  All cysteine residues in the metallothionein interact through a thiol group to coordinate a total of 7 divalent metal ions per protein.<sup>[3]</sup>  These metal-thiolate bonds are quite strong, but what makes the binding of these metals to metallothionein so strong is that when bound the protein will change conformation to wrap almost completely around the coordinated metal ions.<sup>[3]</sup>  For our project we will be taking advantage of this incredibly strong binding to sequester the toxic metals.  
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Metallothionein proteins are highly conserved across species, and one of these commonalities is that they all contain a great number of cysteine residues (approximately 30% of all residues in most metallothioneins).<sup>[2]</sup>  All cysteine residues in the metallothionein interact through a thiol group to coordinate a total of 7 divalent metal ions per protein.<sup>[3]</sup>  These metal-thiolate bonds are quite strong, but what makes the binding of these metals to metallothionein so strong is that when bound the protein will change conformation to wrap almost completely around the coordinated metal ions.<sup>[3]</sup>  For our project we will be taking advantage of this incredibly strong binding to sequester the toxic metals.  
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<a class="thumbnail link" href="https://static.igem.org/mediawiki/2014/d/d8/Cornell_metallothionein_with_CYS.png" data-toggle="lightbox" data-gallery="metal" style="margin-bottom: 0px;">
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Yeast Metallothionein with Cysteines
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<a class="thumbnail link" href="https://static.igem.org/mediawiki/2014/6/65/Cornell_Metallothionein_Pymol.png" data-toggle="lightbox" data-gallery="metal" style="margin-bottom: 0px;">
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<img src="https://static.igem.org/mediawiki/2014/6/65/Cornell_Metallothionein_Pymol.png">
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Yeast Metallothionein Bound to Silver
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Yeast Metallothionein Surface Model
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Yeast Metallothionein with Cysteines
 
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Yeast Metallothionein Bound to Silver
 
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Yeast Metallothionein Surface Model
 
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<h2>GST-YMT</h2>
<h2>GST-YMT</h2>
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The metallothionein gene we are utilizing with is <i>crs5</i>, which codes for YMT, or yeast metallothionein from <i>Saccharomyces cerevisiae</i>.<sup>[4]</sup>  Metallothioneins like YMT are fairly unstable as proteins and are degraded regularly in cells (on the timescale of hours), which would prevent a sequestration system from working effectively.<sup>[2]</sup>  To combat this issue we are working with YMT fused to glutathione-S-transferase from <i>Schistosoma japonicum</i> in a well established fusion protein system.<sup>[5]</sup>  This fusion should help stabilize the metallothionein and prevent action of lyases.  This GST-YMT fusion system has been used previously and we will be utilizing it with a different regulatory system.<sup>[6]</sup>
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The metallothionein we are working with is called CRS5 (used interchangeably with YMT: Yeast Metallothionein) and is from <i>Saccharomyces cerevisiae</i>.<sup>[4]</sup>  Metallothioneins like CRS5 are fairly unstable as proteins and are degraded fairly regularly in cells (on the timescale of hours), which would prevent a sequestration system from working effectively.<sup>[2]</sup>  To combat this issue we are working with CRS5 fused to glutathione-S-transferase from <i>Schistosoma japonicum</i> in a well established fusion protein system.<sup>[5]</sup>  This fusion should help stabilize the metallothionein and prevent action of lyases.  This GST-CRS5 fusion system has been used previously and we will be utilizing it with a different regulatory system.<sup>[6]</sup>
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<ol>
<ol>
<li>Coyle, P., Philcox, J., Carey, L., & Rofe, A. (2002). Metallothionein: The multipurpose protein. <i>Cellular and Molecular Life Sciences</i>, 627-647.</li>
<li>Coyle, P., Philcox, J., Carey, L., & Rofe, A. (2002). Metallothionein: The multipurpose protein. <i>Cellular and Molecular Life Sciences</i>, 627-647.</li>
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<li> Klaassen, C., Liu, J., & Choudhuri, S. (1999). METALLOTHIONEIN: An Intracellular Protein To Protect Against Cadmium Toxicity. <i>Annual Review of Pharmacology and Toxicology</i>,267-294.
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<li> Klaassen, C., Liu, J., & Choudhuri, S. (1999). METALLOTHIONEIN: An Intracellular Protein To Protect Against Cadmium Toxicity. <i>Annual Review of Pharmacology and Toxicology</i>,267-294.</li>
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</li>
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<li>Carpenè, E., Andreani, G., & Isani, G. (2007). Metallothionein functions and structural characteristics. <i>Journal of Trace Elements in Medicine and Biology</i>, 35-39.</li>
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<li>Carpenè, E., Andreani, G., & Isani, G. (2007). Metallothionein functions and structural characteristics. <i>Journal of Trace Elements in Medicine and Biology</i>, 35-39.
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<li>Culotta, V., Howard, W., & Liu, X. (1994). CRS5 encodes a metallothionein-like protein in Saccharomyces cerevisiae. <i>J. Biol. Chem.</i>, 269(41), 25295-25302.</li>
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</li>
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<li>Smith, D., & Johnson, K. (1988). Single-step Purification Of Polypeptides Expressed In <i>Escherichia coli</i> As Fusions With Glutathione S-transferase. <i>Gene<i>, 31-40.</li>
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                                        <li>Culotta, V., Howard, W., & Liu, X. (1994). CRS5 encodes a metallothionein-like protein in Saccharomyces cerevisiae. <i>J. Biol. Chem.</i>, 269(41), 25295-25302.</li>
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<li>Chen, S., & Wilson, D. (1997). Construction and characterization of <i>Escherichia coli</i> genetically engineered for bioremediation of Hg(2+)-contaminated environments. <i>Applied and Environmental Microbiology</i>, 63(6), 2442-2445.</li>
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                                        <li>Smith, D., & Johnson, K. (1988). Single-step Purification Of Polypeptides Expressed In <i>Escherichia coli</i> As Fusions With Glutathione S-transferase. <i>Gene<i>, 31-40.
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</li>
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                                        <li>Chen, S., & Wilson, D. (1997). Construction and characterization of <i>Escherichia coli</i> genetically engineered for bioremediation of Hg(2+)-contaminated environments. <i>Applied and Environmental Microbiology</i>, 63(6), 2442-2445.
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Latest revision as of 03:29, 18 October 2014

Cornell iGEM

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Project Background

What are they?

Metallothioneins are a group of low-molecular-weight proteins that rapidly bind with divalent metal ions.[1] Metallothioneins exist in almost every living organism and have many functions ranging from the control of oxidative stress to the regulation of redox potentials to the protection against toxic heavy metals.[1] For our project, we will take advantage of this final function where our recombinantly expressed metallothioneins will permanently sequester metals intracellularly while simultaneously providing resistance to engineered cells.

Mode of binding

Metallothionein proteins across species have highly conserved sequences with approximately 30% of all residues as cysteines.[2] All cysteine residues in the metallothionein interact through a thiol group to coordinate a total of 7 divalent metal ions per protein.[3] These metal-thiolate bonds are quite strong, but what makes the binding of these metals to metallothionein so strong is that when bound the protein will change conformation to wrap almost completely around the coordinated metal ions.[3] For our project we will be taking advantage of this incredibly strong binding to sequester the toxic metals.

GST-YMT

The metallothionein gene we are utilizing with is crs5, which codes for YMT, or yeast metallothionein from Saccharomyces cerevisiae.[4] Metallothioneins like YMT are fairly unstable as proteins and are degraded regularly in cells (on the timescale of hours), which would prevent a sequestration system from working effectively.[2] To combat this issue we are working with YMT fused to glutathione-S-transferase from Schistosoma japonicum in a well established fusion protein system.[5] This fusion should help stabilize the metallothionein and prevent action of lyases. This GST-YMT fusion system has been used previously and we will be utilizing it with a different regulatory system.[6]

References


  1. Coyle, P., Philcox, J., Carey, L., & Rofe, A. (2002). Metallothionein: The multipurpose protein. Cellular and Molecular Life Sciences, 627-647.
  2. Klaassen, C., Liu, J., & Choudhuri, S. (1999). METALLOTHIONEIN: An Intracellular Protein To Protect Against Cadmium Toxicity. Annual Review of Pharmacology and Toxicology,267-294.
  3. Carpenè, E., Andreani, G., & Isani, G. (2007). Metallothionein functions and structural characteristics. Journal of Trace Elements in Medicine and Biology, 35-39.
  4. Culotta, V., Howard, W., & Liu, X. (1994). CRS5 encodes a metallothionein-like protein in Saccharomyces cerevisiae. J. Biol. Chem., 269(41), 25295-25302.
  5. Smith, D., & Johnson, K. (1988). Single-step Purification Of Polypeptides Expressed In Escherichia coli As Fusions With Glutathione S-transferase. Gene, 31-40.
  6. Chen, S., & Wilson, D. (1997). Construction and characterization of Escherichia coli genetically engineered for bioremediation of Hg(2+)-contaminated environments. Applied and Environmental Microbiology, 63(6), 2442-2445.