Lac repressor: Difference between revisions
Eric Martz (talk | contribs) →Structure of the lac repressor: adding content |
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<table align='right'><tr><td> </td><td>{{Template:ColorKey_ConSurf}}</td></tr></table> | <table align='right'><tr><td> </td><td>{{Template:ColorKey_ConSurf}}</td></tr></table> | ||
The most highly <scene name='Lac_repressor/1lbg_lac_repressor_with_dna/6'>conserved surface on the lac repressor</scene> is the surface that contacts DNA<ref>Conservation results for [[1lbg]] are from the precalculated [http://consurfdb.tau.ac.il ConSurf Database], using 103 sequences from Swiss-Prot with an average pairwise distance of 2.4.</ref>. (Only alpha carbon atoms are shown here, without sidechains, because sidechains were not resolved in the 4.8 Å [[1lbg]] model.) The dimerization surfaces are the most conserved sides of the ligand-binding domains<ref>Conservation results for [[ | The most highly <scene name='Lac_repressor/1lbg_lac_repressor_with_dna/6'>conserved surface on the lac repressor</scene> is the surface that contacts DNA<ref>Conservation results for [[1lbg]] are from the precalculated [http://consurfdb.tau.ac.il ConSurf Database], using 103 sequences from Swiss-Prot with an average pairwise distance of 2.4.</ref>. (Only alpha carbon atoms are shown here, without sidechains, because sidechains were not resolved in the 4.8 Å [[1lbg]] model.) The dimerization surfaces are the <scene name='Lac_repressor/1lbi_apo_lac_repressor/4'>most conserved sides</scene> of the ligand-binding domains<ref>Conservation results for [[1lbi]] are from the [http://consurf.tau.ac.il ConSurf Server], using 100 sequences from Uniprot with an average pairwise distance of 1.3.</ref>. (This scene shows sidechains, using the 2.7 Å model in [[1lbi]], which lacks the DNA-binding domain due to disorder.) | ||
The C-terminal tetramerization helices tether two dimers, enabling lac repressor to function as a homo-tetramer. | The C-terminal tetramerization helices tether two dimers, enabling lac repressor to function as a homo-tetramer. | ||
Revision as of 00:00, 15 October 2008
What is the lac repressor?What is the lac repressor?
Repressors are proteins that inhibit the expression of genes; that is, they inhibit the transcription of messenger RNA from their target genes. Each repressor targets a specific co-regulated group of genes by recognizing a specific sequence of DNA, called the operator in bacteria. Repressor proteins are coded for by regulatory genes.
The lactose ("lac") repressor controls the expression of bacterial enzymes involved in the metabolism of of the sugar lactose. When the lac repressor binds lactose, it changes to an inactive conformation that cannot repress the production of these enzymes. Thus, the enzymes needed to use lactose are made only when lactose is available. The lac repressor, and the group of genes it controls, which is called an operon, were the first such gene regulatory system to be discovered. The operon was described in 1960[1] by François Jacob et al., who also correctly proposed the general mechanism of regulation by the lac repressor. The 1965 Nobel Prize in Physiology or Medicine was awarded to François Jacob, André Lwoff, and Jacques Monod "for their discoveries concerning genetic control of enzyme and virus synthesis".
For a general introduction to the lac repressor, please see David Goodsell's Introduction to the lac repressor in his series Molecule of the Month, and the article in Wikipedia on the lac repressor. Mitchell Lewis published a detailed review in 2005[2].
Structure of the lac repressorStructure of the lac repressor
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The lac repressor protein ( showing chain A in 1lbg, resolution 4.8 Å), starting at the N-terminus, begins with a DNA-binding "headpiece", followed by a hinge region, then an N-terminal ligand-binding subdomain and a C-terminal ligand binding subdomain, a linker, and a C-terminal tetramerization helix[3]. In the absence of DNA, the hinge region does not form the alpha helix shown here.
As can be seen when the chain is
| N | C |
each of the ligand-binding subdomains is made up of two discontinuous segments.
The lac repressor forms . Dimerization buries 2,200 Å2 of surface, including a ,
forming a hydrophobic core (shown with 1lbi, resolution 2.7 Å, where the DNA-binding domain is disordered).
 |
The most highly is the surface that contacts DNA[4]. (Only alpha carbon atoms are shown here, without sidechains, because sidechains were not resolved in the 4.8 Å 1lbg model.) The dimerization surfaces are the of the ligand-binding domains[5]. (This scene shows sidechains, using the 2.7 Å model in 1lbi, which lacks the DNA-binding domain due to disorder.)
The C-terminal tetramerization helices tether two dimers, enabling lac repressor to function as a homo-tetramer.
To Be Continued .... Eric Martz 16:22, 14 October 2008 (IST)
ReferencesReferences
- ↑ L'opéron: groupe de gènes à expression coordonée par un opérateur. [Operon: a group of genes with the expression coordinated by an operator.] C R Hebd Seances Acad Sci., 250:1727-9, 1960. PubMed 14406329
- ↑ The lac repressor. Lewis, M. C R Biol. 328:521-48, 2005. PubMed 15950160
- ↑ This domain coloring scheme is adapted from Fig. 6 in the review by Lewis (C. R. Biol. 328:521, 2005). Domains are 1-45, 46-62, (63-162,291-320), (163-290,321-332), 330-339, and 340-357.
- ↑ Conservation results for 1lbg are from the precalculated ConSurf Database, using 103 sequences from Swiss-Prot with an average pairwise distance of 2.4.
- ↑ Conservation results for 1lbi are from the ConSurf Server, using 100 sequences from Uniprot with an average pairwise distance of 1.3.