1em8: Difference between revisions

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Crystal structure of chi and psi subunit heterodimer from DNA POL III

OverviewOverview

The chi (chi) and psi (psi) subunits of Escherichia coli DNA polymerase III form a heterodimer that is associated with the ATP-dependent clamp-loader machinery. In E. coli, the chi:psi heterodimer serves as a bridge between the clamp-loader complex and the single-stranded DNA-binding protein. We determined the crystal structure of the chi:psi heterodimer at 2.1 A resolution. Although neither chi (147 residues) nor psi (137 residues) bind to nucleotides, the fold of each protein is similar to the folds of mononucleotide-(chi) or dinucleotide-(psi) binding proteins, without marked similarity to the structures of the clamp-loader subunits. Genes encoding chi and psi proteins are found to be readily identifiable in several bacterial genomes and sequence alignments showed that residues at the chi:psi interface are highly conserved in both proteins, suggesting that the heterodimeric interaction is of functional significance. The conservation of surface-exposed residues is restricted to the interfacial region and to just two other regions in the chi:psi complex. One of the conserved regions was found to be located on chi, distal to the psi interaction region, and we identified this as the binding site for a C-terminal segment of the single-stranded DNA-binding protein. The other region of sequence conservation is localized to an N-terminal segment of psi (26 residues) that is disordered in the crystal structure. We speculate that psi is linked to the clamp-loader complex by this flexible, but conserved, N-terminal segment, and that the chi:psi unit is linked to the single-stranded DNA-binding protein via the distal surface of chi. The base of the clamp-loader complex has an open C-shaped structure, and the shape of the chi:psi complex is suggestive of a loose docking within the crevice formed by the open faces of the delta and delta' subunits of the clamp-loader.

About this StructureAbout this Structure

1EM8 is a Protein complex structure of sequences from Escherichia coli. Active as DNA-directed DNA polymerase, with EC number 2.7.7.7 Full crystallographic information is available from OCA.

ReferenceReference

Crystal structure of the chi:psi sub-assembly of the Escherichia coli DNA polymerase clamp-loader complex., Gulbis JM, Kazmirski SL, Finkelstein J, Kelman Z, O'Donnell M, Kuriyan J, Eur J Biochem. 2004 Jan;271(2):439-49. PMID:14717711

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-[[Image:1em8.gif|left|200px]]<br /><applet load="1em8" size="450" color="white" frame="true" align="right" spinBox="true"
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 '''Crystal structure of chi and psi subunit heterodimer from DNA POL III'''<br />
 ==Overview==
-The chi (chi) and psi (psi) subunits of Escherichia coli DNA polymerase, III form a heterodimer that is associated with the ATP-dependent, clamp-loader machinery. In E. coli, the chi:psi heterodimer serves as a, bridge between the clamp-loader complex and the single-stranded, DNA-binding protein. We determined the crystal structure of the chi:psi, heterodimer at 2.1 A resolution. Although neither chi (147 residues) nor, psi (137 residues) bind to nucleotides, the fold of each protein is, similar to the folds of mononucleotide-(chi) or dinucleotide-(psi) binding, proteins, without marked similarity to the structures of the clamp-loader, subunits. Genes encoding chi and psi proteins are found to be readily, identifiable in several bacterial genomes and sequence alignments showed, that residues at the chi:psi interface are highly conserved in both, proteins, suggesting that the heterodimeric interaction is of functional, significance. The conservation of surface-exposed residues is restricted, to the interfacial region and to just two other regions in the chi:psi, complex. One of the conserved regions was found to be located on chi, distal to the psi interaction region, and we identified this as the, binding site for a C-terminal segment of the single-stranded DNA-binding, protein. The other region of sequence conservation is localized to an, N-terminal segment of psi (26 residues) that is disordered in the crystal, structure. We speculate that psi is linked to the clamp-loader complex by, this flexible, but conserved, N-terminal segment, and that the chi:psi, unit is linked to the single-stranded DNA-binding protein via the distal, surface of chi. The base of the clamp-loader complex has an open C-shaped, structure, and the shape of the chi:psi complex is suggestive of a loose, docking within the crevice formed by the open faces of the delta and, delta' subunits of the clamp-loader.
+The chi (chi) and psi (psi) subunits of Escherichia coli DNA polymerase III form a heterodimer that is associated with the ATP-dependent clamp-loader machinery. In E. coli, the chi:psi heterodimer serves as a bridge between the clamp-loader complex and the single-stranded DNA-binding protein. We determined the crystal structure of the chi:psi heterodimer at 2.1 A resolution. Although neither chi (147 residues) nor psi (137 residues) bind to nucleotides, the fold of each protein is similar to the folds of mononucleotide-(chi) or dinucleotide-(psi) binding proteins, without marked similarity to the structures of the clamp-loader subunits. Genes encoding chi and psi proteins are found to be readily identifiable in several bacterial genomes and sequence alignments showed that residues at the chi:psi interface are highly conserved in both proteins, suggesting that the heterodimeric interaction is of functional significance. The conservation of surface-exposed residues is restricted to the interfacial region and to just two other regions in the chi:psi complex. One of the conserved regions was found to be located on chi, distal to the psi interaction region, and we identified this as the binding site for a C-terminal segment of the single-stranded DNA-binding protein. The other region of sequence conservation is localized to an N-terminal segment of psi (26 residues) that is disordered in the crystal structure. We speculate that psi is linked to the clamp-loader complex by this flexible, but conserved, N-terminal segment, and that the chi:psi unit is linked to the single-stranded DNA-binding protein via the distal surface of chi. The base of the clamp-loader complex has an open C-shaped structure, and the shape of the chi:psi complex is suggestive of a loose docking within the crevice formed by the open faces of the delta and delta' subunits of the clamp-loader.
 ==About this Structure==
-EM8 is a [http://en.wikipedia.org/wiki/Protein_complex Protein complex] structure of sequences from [http://en.wikipedia.org/wiki/Escherichia_coli Escherichia coli]. Active as [http://en.wikipedia.org/wiki/DNA-directed_DNA_polymerase DNA-directed DNA polymerase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=2.7.7.7 2.7.7.7] Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1EM8 OCA].
+EM8 is a [http://en.wikipedia.org/wiki/Protein_complex Protein complex] structure of sequences from [http://en.wikipedia.org/wiki/Escherichia_coli Escherichia coli]. Active as [http://en.wikipedia.org/wiki/DNA-directed_DNA_polymerase DNA-directed DNA polymerase], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=2.7.7.7 2.7.7.7] Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=1EM8 OCA].
 ==Reference==
@@ Line 14: / Line 14: @@
 [[Category: Escherichia coli]]
 [[Category: Protein complex]]
-[[Category: Donnell, M.O.]]
+[[Category: Donnell, M O.]]
 [[Category: Finkelstein, J.]]
-[[Category: Gulbis, J.M.]]
+[[Category: Gulbis, J M.]]
 [[Category: Kuriyan, J.]]
 [[Category: alpha-beta fold]]
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 [[Category: heterodimer]]
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