331d: Difference between revisions

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==Overview==

The crystal structure of the DNA heptamer d(GCGCGCG) has been solved at, 1.65 A resolution by the molecular replacement method and refined to an, R-value of 0.184 for 3598 reflections. The heptamer forms a Z-DNA, d(CGCGCG)2 with 5'-overhang G residues instead of an A-DNA d(GCGCGC)2 with, 3'-overhang G residues. The overhang G residues from parallel strands of, two adjacent duplexes form a trans reverse Hoogsteen G x G basepair that, stacks on the six Z-DNA basepairs to produce a pseudocontinuous helix. The, reverse Hoogsteen G x G basepair is unusual in that the displacement of, one G base relative to the other allows them to participate in a, bifurcated (G1)N2 . . . N7(G8) and an enhanced (G8)C8-H . . . O6(G1), hydrogen bond, in addition to the two usual hydrogen bonds. The, 5'-overhang G residues are anti and C2'-endo while the 3'-terminal G, residues are syn and C2'-endo. The conformations of both G residues are, different from the syn/C3'-endo for the guanosine in a standard Z-DNA. The, two cobalt hexammine ions bind to the phosphate groups in both GpC and CpG, steps in Z(I) and Z(II) conformations. The water structure motif is, similar to the other Z-DNA structures.

The crystal structure of the DNA heptamer d(GCGCGCG) has been solved at 1.65 A resolution by the molecular replacement method and refined to an R-value of 0.184 for 3598 reflections. The heptamer forms a Z-DNA d(CGCGCG)2 with 5'-overhang G residues instead of an A-DNA d(GCGCGC)2 with 3'-overhang G residues. The overhang G residues from parallel strands of two adjacent duplexes form a trans reverse Hoogsteen G x G basepair that stacks on the six Z-DNA basepairs to produce a pseudocontinuous helix. The reverse Hoogsteen G x G basepair is unusual in that the displacement of one G base relative to the other allows them to participate in a bifurcated (G1)N2 . . . N7(G8) and an enhanced (G8)C8-H . . . O6(G1) hydrogen bond, in addition to the two usual hydrogen bonds. The 5'-overhang G residues are anti and C2'-endo while the 3'-terminal G residues are syn and C2'-endo. The conformations of both G residues are different from the syn/C3'-endo for the guanosine in a standard Z-DNA. The two cobalt hexammine ions bind to the phosphate groups in both GpC and CpG steps in Z(I) and Z(II) conformations. The water structure motif is similar to the other Z-DNA structures.

==About this Structure==

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[[Category: z-dna]]

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@@ Line 4: / Line 4: @@
 ==Overview==
-The crystal structure of the DNA heptamer d(GCGCGCG) has been solved at, 1.65 A resolution by the molecular replacement method and refined to an, R-value of 0.184 for 3598 reflections. The heptamer forms a Z-DNA, d(CGCGCG)2 with 5'-overhang G residues instead of an A-DNA d(GCGCGC)2 with, 3'-overhang G residues. The overhang G residues from parallel strands of, two adjacent duplexes form a trans reverse Hoogsteen G x G basepair that, stacks on the six Z-DNA basepairs to produce a pseudocontinuous helix. The, reverse Hoogsteen G x G basepair is unusual in that the displacement of, one G base relative to the other allows them to participate in a, bifurcated (G1)N2 . . . N7(G8) and an enhanced (G8)C8-H . . . O6(G1), hydrogen bond, in addition to the two usual hydrogen bonds. The, 5'-overhang G residues are anti and C2'-endo while the 3'-terminal G, residues are syn and C2'-endo. The conformations of both G residues are, different from the syn/C3'-endo for the guanosine in a standard Z-DNA. The, two cobalt hexammine ions bind to the phosphate groups in both GpC and CpG, steps in Z(I) and Z(II) conformations. The water structure motif is, similar to the other Z-DNA structures.
+The crystal structure of the DNA heptamer d(GCGCGCG) has been solved at 1.65 A resolution by the molecular replacement method and refined to an R-value of 0.184 for 3598 reflections. The heptamer forms a Z-DNA d(CGCGCG)2 with 5'-overhang G residues instead of an A-DNA d(GCGCGC)2 with 3'-overhang G residues. The overhang G residues from parallel strands of two adjacent duplexes form a trans reverse Hoogsteen G x G basepair that stacks on the six Z-DNA basepairs to produce a pseudocontinuous helix. The reverse Hoogsteen G x G basepair is unusual in that the displacement of one G base relative to the other allows them to participate in a bifurcated (G1)N2 . . . N7(G8) and an enhanced (G8)C8-H . . . O6(G1) hydrogen bond, in addition to the two usual hydrogen bonds. The 5'-overhang G residues are anti and C2'-endo while the 3'-terminal G residues are syn and C2'-endo. The conformations of both G residues are different from the syn/C3'-endo for the guanosine in a standard Z-DNA. The two cobalt hexammine ions bind to the phosphate groups in both GpC and CpG steps in Z(I) and Z(II) conformations. The water structure motif is similar to the other Z-DNA structures.
 ==About this Structure==
@@ Line 22: / Line 22: @@
 [[Category: z-dna]]
-''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Tue Jan 29 21:35:35 2008''
+''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Thu Feb 21 19:02:04 2008''