2tct
From Proteopedia
(New page: 200px<br /><applet load="2tct" size="450" color="white" frame="true" align="right" spinBox="true" caption="2tct, resolution 2.1Å" /> '''THE COMPLEX FORMED BE...) |
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| - | [[Image:2tct.gif|left|200px]]<br /><applet load="2tct" size=" | + | [[Image:2tct.gif|left|200px]]<br /><applet load="2tct" size="350" color="white" frame="true" align="right" spinBox="true" |
caption="2tct, resolution 2.1Å" /> | caption="2tct, resolution 2.1Å" /> | ||
'''THE COMPLEX FORMED BETWEEN TET REPRESSOR AND TETRACYCLINE-MG2+ REVEALS MECHANISM OF ANTIBIOTIC RESISTANCE'''<br /> | '''THE COMPLEX FORMED BETWEEN TET REPRESSOR AND TETRACYCLINE-MG2+ REVEALS MECHANISM OF ANTIBIOTIC RESISTANCE'''<br /> | ||
==Overview== | ==Overview== | ||
| - | In recent years Gram-negative bacteria have developed several resistance | + | In recent years Gram-negative bacteria have developed several resistance mechanisms against the broad-spectrum antibiotic tetracycline (Tc). The most abundant mechanism involves a membrane-associated protein (TetA) that exports the antibiotic out of the bacterial cell before it can attach to the ribosomes and inhibit polypeptide elongation. The expression of the TetA protein is regulated by the Tet repressor (TetR). It occurs as a homodimer and binds with two alpha-helix-turn-alpha-helix motifs (HTH) to two tandemly orientated DNA operators, thereby blocking the expression of the associated genes, one encoding for TetA and the other for TetR. If Tc in complex with a divalent cation binds to TetR, a conformational change occurs and the induced TetR is then unable to bind to DNA. TetR of class D, TEtRD, was cocrystallized with tetracycline (7HTc) and Mg2+ in space group I4(1)22 and studied by X-ray diffraction. One TetRD monomer occupies the crystal asymmetric unit, and the dimer is formed by a crystallographic 2-fold rotation. The crystal structure was determined by multiple isomorphous replacement at 2.5 A resolution, and on this basis the structure of the nearly isomorphous complex with 7-chlorotetracycline, TetRD/(Mg 7CITc)+, has been refined to an R-factor of 18.3% using all reflections to 2.1 A resolution. TetRD folds into ten alpha-helices with connecting turns and loops. The N-terminal three alpha-helices of the repressor form the DNA-binding domain, including the HTH with an inverse orientation compared with HTH in other DNA-binding proteins. The distance of 39 A between the two recognition helices explains the inability of the induced TetR to bind to B-form DNA. The core of the protein is formed by helices alpha 5 to alpha 10. It is responsible for dimerization and contains, for each monomer, a binding pocket that accommodates Tc in the presence of a divalent cation. The structure of the TetRD/(Mg 7CITc)+ complex reveals the octahedral coordination of Mg2+ by Tc (chelating O-11, and O-12), His100 N epsilon and by three water molecules; in addition there is an extended network of hydrogen bonding and van der Waals interactions formed between 7CITc and TetR. The detailed view of the Tc-binding pocket and the interactions between the antibiotic and the repressor offers the first solid basis for rational tetracycline design, with the aim of circumventing resistance. |
==About this Structure== | ==About this Structure== | ||
| - | 2TCT is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Escherichia_coli Escherichia coli] with MG and CTC as [http://en.wikipedia.org/wiki/ligands ligands]. This structure | + | 2TCT is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Escherichia_coli Escherichia coli] with <scene name='pdbligand=MG:'>MG</scene> and <scene name='pdbligand=CTC:'>CTC</scene> as [http://en.wikipedia.org/wiki/ligands ligands]. This structure supersedes the now removed PDB entry 1TCT. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=2TCT OCA]. |
==Reference== | ==Reference== | ||
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[[Category: transcription regulation]] | [[Category: transcription regulation]] | ||
| - | ''Page seeded by [http:// | + | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 18:49:38 2008'' |
Revision as of 16:49, 21 February 2008
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THE COMPLEX FORMED BETWEEN TET REPRESSOR AND TETRACYCLINE-MG2+ REVEALS MECHANISM OF ANTIBIOTIC RESISTANCE
Overview
In recent years Gram-negative bacteria have developed several resistance mechanisms against the broad-spectrum antibiotic tetracycline (Tc). The most abundant mechanism involves a membrane-associated protein (TetA) that exports the antibiotic out of the bacterial cell before it can attach to the ribosomes and inhibit polypeptide elongation. The expression of the TetA protein is regulated by the Tet repressor (TetR). It occurs as a homodimer and binds with two alpha-helix-turn-alpha-helix motifs (HTH) to two tandemly orientated DNA operators, thereby blocking the expression of the associated genes, one encoding for TetA and the other for TetR. If Tc in complex with a divalent cation binds to TetR, a conformational change occurs and the induced TetR is then unable to bind to DNA. TetR of class D, TEtRD, was cocrystallized with tetracycline (7HTc) and Mg2+ in space group I4(1)22 and studied by X-ray diffraction. One TetRD monomer occupies the crystal asymmetric unit, and the dimer is formed by a crystallographic 2-fold rotation. The crystal structure was determined by multiple isomorphous replacement at 2.5 A resolution, and on this basis the structure of the nearly isomorphous complex with 7-chlorotetracycline, TetRD/(Mg 7CITc)+, has been refined to an R-factor of 18.3% using all reflections to 2.1 A resolution. TetRD folds into ten alpha-helices with connecting turns and loops. The N-terminal three alpha-helices of the repressor form the DNA-binding domain, including the HTH with an inverse orientation compared with HTH in other DNA-binding proteins. The distance of 39 A between the two recognition helices explains the inability of the induced TetR to bind to B-form DNA. The core of the protein is formed by helices alpha 5 to alpha 10. It is responsible for dimerization and contains, for each monomer, a binding pocket that accommodates Tc in the presence of a divalent cation. The structure of the TetRD/(Mg 7CITc)+ complex reveals the octahedral coordination of Mg2+ by Tc (chelating O-11, and O-12), His100 N epsilon and by three water molecules; in addition there is an extended network of hydrogen bonding and van der Waals interactions formed between 7CITc and TetR. The detailed view of the Tc-binding pocket and the interactions between the antibiotic and the repressor offers the first solid basis for rational tetracycline design, with the aim of circumventing resistance.
About this Structure
2TCT is a Single protein structure of sequence from Escherichia coli with and as ligands. This structure supersedes the now removed PDB entry 1TCT. Full crystallographic information is available from OCA.
Reference
The complex formed between Tet repressor and tetracycline-Mg2+ reveals mechanism of antibiotic resistance., Kisker C, Hinrichs W, Tovar K, Hillen W, Saenger W, J Mol Biol. 1995 Mar 24;247(2):260-80. PMID:7707374
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