Lauren Ferris/Sandbox 2

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'''The DdrB Core'''
'''The DdrB Core'''
[[Image:OB fold.jpg|300px|left|thumb|This figure highlights the differences between the classic OB fold found in single-stranded binding proteins and the novel structural features of DdrB. The OB fold is observed in the protein verotoxin-1, PDB code [[2XSC]] . DdrB is modeled from the PDB structure [[4HQB]]. This figure was generated using Pymol.]]This is followed by <scene name='57/578563/4exw_monomer_6b/1'>6 beta strands</scene>, which contain a solvent exposed face and another face that against the N-terminal motif. The beta sheets are anti-parallel and do not form an OB fold as determined by multiple servers iCOPS, DALI, 3D-BLAST, and MATRAS.<ref>PMID: 20129942</ref> At the time of this finding (2010), the lack of an OB fold was surprising, since all ssDNA binding proteins were thought to bind to DNA through an OB fold. The OB fold is two three-stranded anti-parallel β sheets that form a five stranded β barrel. The OB folds adopt greek key motifs. The differences between the DdrB beta strands and those in the OB fold include the topology of the β strands. DdrB strands form an up and down topology and not a Greek key. Furthermore, monomeric DdrB β strands do not form a beta barrel. Additionally, DdrB has different connectivity, no conserved glycine, and no β bulge.<ref>PMID: 20129942</ref>
[[Image:OB fold.jpg|300px|left|thumb|This figure highlights the differences between the classic OB fold found in single-stranded binding proteins and the novel structural features of DdrB. The OB fold is observed in the protein verotoxin-1, PDB code [[2XSC]] . DdrB is modeled from the PDB structure [[4HQB]]. This figure was generated using Pymol.]]This is followed by <scene name='57/578563/4exw_monomer_6b/1'>6 beta strands</scene>, which contain a solvent exposed face and another face that against the N-terminal motif. The beta sheets are anti-parallel and do not form an OB fold as determined by multiple servers iCOPS, DALI, 3D-BLAST, and MATRAS.<ref>PMID: 20129942</ref> At the time of this finding (2010), the lack of an OB fold was surprising, since all ssDNA binding proteins were thought to bind to DNA through an OB fold. The OB fold is two three-stranded anti-parallel β sheets that form a five stranded β barrel. The OB folds adopt greek key motifs. The differences between the DdrB beta strands and those in the OB fold include the topology of the β strands. DdrB strands form an up and down topology and not a Greek key. Furthermore, monomeric DdrB β strands do not form a beta barrel. Additionally, DdrB has different connectivity, no conserved glycine, and no β bulge.<ref>PMID: 20129942</ref>
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[[Image:electrostatics monomer.jpg|300px|left|thumb|The electrostatic charges in the DdrB monomer. Blue represents positive charges, while red represents negative charges. (PDB: [[4HQB]]). This figure was generated using Pymol.]]
[[Image:electrostatics monomer.jpg|300px|left|thumb|The electrostatic charges in the DdrB monomer. Blue represents positive charges, while red represents negative charges. (PDB: [[4HQB]]). This figure was generated using Pymol.]]
Positively Charged amino acids reside in the solvent exposed beta strands, which may potentially enable the binding of ssDNA.
Positively Charged amino acids reside in the solvent exposed beta strands, which may potentially enable the binding of ssDNA.
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<scene name='57/578563/4exw_monomer_loops/1'>Two loops</scene> that link beta sheet 6 to sheet 7 and beta sheet 7 to sheet 8 contain flexible regions with poor order as determined by limited to no density in the crystal structure. This finding suggests that these loops are intrinsically disordered.<ref>PMID: 20129942</ref>
 
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'''The C-terminal Domain'''
 
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The C-terminal domain also contains regions with predicted intrinsic disorder.<ref>PMID: 20129942</ref> The PSIpred server predicts that the last 35 residues of Deinococcus geothermalis are disordered. This prediction is supported by the solved crystal structure as the last 51 residues could not be determined. While, the structure of the C-terminal end is not known, it may still be of interest. A BLAST search revealed an 83 amino acid protein in Deinococcus geothermalis with 72% similarity and 62% identity to the disordered region of the C-terminus.<ref>PMID: 20129942</ref> However, the function of this protein remains unknown. One hypothesis is that this region may mediate protein-protein interactions. Single stranded binding proteins also have disordered C-termini and contain negatively charged residues that mediate protein-protein interactions. As DdrB contains several conserved negatively charged residues it is thought that the C-terminus of this protein could also mediate protein-protein interactions.<ref>PMID: 20129942</ref> However, this hypothesis may be debated as the C-terminus was not needed for radioresistance in Deinococcus radiodurans.<ref>PMID: 21968057</ref>
 
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<scene name='57/578563/4exw_monomer_loops/1'>Two loops</scene> that link beta sheet 6 to sheet 7 and beta sheet 7 to sheet 8 contain flexible regions with poor order as determined by limited to no density in the crystal structure. This finding suggests that these loops are intrinsically disordered.<ref>PMID: 20129942</ref>
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'''The C-terminal Domain'''
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The C-terminal domain also contains regions with predicted intrinsic disorder.<ref>PMID: 20129942</ref> The PSIpred server predicts that the last 35 residues of Deinococcus geothermalis are disordered. This prediction is supported by the solved crystal structure as the last 51 residues could not be determined. While, the structure of the C-terminal end is not known, it may still be of interest. A BLAST search revealed an 83 amino acid protein in Deinococcus geothermalis with 72% similarity and 62% identity to the disordered region of the C-terminus.<ref>PMID: 20129942</ref> However, the function of this protein remains unknown. One hypothesis is that this region may mediate protein-protein interactions. Single stranded binding proteins also have disordered C-termini and contain negatively charged residues that mediate protein-protein interactions. As DdrB contains several conserved negatively charged residues it is thought that the C-terminus of this protein could also mediate protein-protein interactions.<ref>PMID: 20129942</ref> However, this hypothesis may be debated as the C-terminus was not needed for radioresistance in Deinococcus radiodurans.<ref>PMID: 21968057</ref>
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===DdrB Pentamer===
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The monomeric units of DdrB collectively form a <scene name='57/578563/4exw_pentamer/1'>pentameric ring </scene>with a 10 A pore in the center of this structure.<ref>PMID: 20129942</ref> Other DNA binding proteins can thread DNA through a central pore, however this seems highly unlikely in the case of DdrB. The pore size appears too small (would need to be 14-40A) and has a net negative charge making it highly unfavorable for DNA interactions.<ref>PMID: 20129942</ref> The beta-beta-alpha motif at the N-terminus of the monomer facilitates the formation of this <scene name='57/578563/Start_molecule_and_bbar/1'> pore </scene> as the beta sheets of the N-terminal beta-beta-alpha motif form a 10 stranded <scene name='57/578563/B_barrel/1'>anti-parallel B-barrel</scene>. This structure is stabilized by interactions with the alpha helices. <ref>PMID: 20129942</ref>
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[[Image:electrostatics pentamer.jpg|300px|left|thumb|The electrostatic charges in the DdrB pentamer. Blue represents positive charges, while red represents negative charges. A positive “track” around the top of the pentamer may enable ssDNA binding to one side of the pentamer (left image). (PDB: [[4HQB]]). This figure was generated using Pymol.]]
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The pentamer also contains a positive residue track on one side of the pentamer. These residues facilitate ssDNA binding and DdrB functionality. <ref>PMID: 20129942</ref>
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===DdrB Pentamer===
 
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The monomeric units of DdrB collectively form a <scene name='57/578563/4exw_pentamer/1'>pentameric ring </scene>with a 10 A pore in the center of this structure.<ref>PMID: 20129942</ref> Other DNA binding proteins can thread DNA through a central pore, however this seems highly unlikely in the case of DdrB. The pore size appears too small (would need to be 14-40A) and has a net negative charge making it highly unfavorable for DNA interactions.<ref>PMID: 20129942</ref> The beta-beta-alpha motif at the N-terminus of the monomer facilitates the formation of this <scene name='57/578563/Start_molecule_and_bbar/1'> pore </scene> as the beta sheets of the N-terminal beta-beta-alpha motif form a 10 stranded <scene name='57/578563/B_barrel/1'>anti-parallel B-barrel</scene>. This structure is stabilized by interactions with the alpha helices. <ref>PMID: 20129942</ref>
 
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The pentamer also contains a positive residue track on one side of the pentamer. These residues facilitate ssDNA binding and DdrB functionality. <ref>PMID: 20129942</ref> [[Image:electrostatics pentamer.jpg|300px|left|thumb|The electrostatic charges in the DdrB pentamer. Blue represents positive charges, while red represents negative charges. A positive “track” around the top of the pentamer may enable ssDNA binding to one side of the pentamer (left image). (PDB: [[4HQB]]). This figure was generated using Pymol.]]
 
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==Structural features that relate to function==
==Structural features that relate to function==

Revision as of 12:04, 30 April 2014

DdrB

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Lauren Ferris

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