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| - | [[Image:1bjy.jpg|left|200px]] | + | #REDIRECT [[4v2g]] This PDB entry is obsolete and replaced by 4v2g |
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| - | {{STRUCTURE_1bjy| PDB=1bjy | SCENE= }}
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| - | '''TETRACYCLINE CHELATED MG2+-ION INITIATES HELIX UNWINDING FOR TET REPRESSOR INDUCTION'''
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| - | ==Overview==
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| - | The homodimeric tetracycline repressor (TetR) regulates resistance to the antibiotic tetracycline at the transcriptional level. TetR binds in the absence of Tc to palindromic operator sequences utilizing two helix-turn-helix (HTH) motifs. If the tetracycline-Mg2+ complex [MgTc]+ enters two identical binding tunnels buried within the TetR homodimer, a conformational change takes place, and the induced [TetR/[MgTc]+]2 complex releases operator DNA. To demonstrate the contribution of Mg2+ to [MgTc]+ binding and TetR induction, the Mg2+ concentration in the induced TetR homodimer was progressively reduced by addition of EDTA, resulting in two X-ray crystal structures of Mg2+-free and half-occupied TetR(D). Tc remains bound to the [MgTc]+-binding sites, despite the complete or partial absence of Mg2+. Together with inducer-free TetR(D), the structures were refined to between 2.2 and 2.7 A resolution and compared with fully induced TetR(D) in complex with two [MgTc]+. Each inducer binding tunnel has three constituent parts, one hydrophobic and two hydrophilic ones. One of the hydrophilic contact areas binds Tc by hydrogen bonding; the hydrophobic region correctly positions Tc and partially closes the entrance to the binding tunnel; the second hydrophilic region coordinates Mg2+, transduces the induction signal, and completes the process of closing the tunnel entrance. Tc confers binding specificity to TetR while Mg2+ is primarily responsible for induction: After binding to the imidazole Nepsilon of His100, Mg2+ is octahedrally coordinated to the 1,3-ketoenolate group of Tc and to three water molecules. One of these waters forms a hydrogen bond to the hydroxyl group Ogamma of Thr103. The induced 2.5 A movement of Thr103 results in the partial unwinding of helix alpha6, associated with a lateral shift of helices alpha4 and alpha9. They simultaneously close the tunnel entrance and cause the DNA-binding domains to adopt a nonbinding conformation, leading to release of operator DNA and expression of the genes responsible for resistance.
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| - | ==About this Structure==
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| - | 1BJY is a [[Single protein]] structure of sequence from [http://en.wikipedia.org/wiki/Escherichia_coli Escherichia coli]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1BJY OCA].
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| - | ==Reference==
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| - | Tetracycline-chelated Mg2+ ion initiates helix unwinding in Tet repressor induction., Orth P, Saenger W, Hinrichs W, Biochemistry. 1999 Jan 5;38(1):191-8. PMID:[http://www.ncbi.nlm.nih.gov/pubmed/9890898 9890898]
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| - | [[Category: Escherichia coli]]
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| - | [[Category: Single protein]]
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| - | [[Category: Hinrichs, W.]]
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| - | [[Category: Orth, P.]]
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| - | [[Category: Saenger, W.]]
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| - | [[Category: Dna-binding protein]]
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| - | [[Category: Hth-motif]]
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| - | [[Category: Transcription regulation]]
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| - | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 11:36:45 2008''
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