1l4j

[[Image:1l4j.gif|left|200px]]<br /><applet load="1l4j" size="450" color="white" frame="true" align="right" spinBox="true"

caption="1l4j, resolution 1.85&Aring;" />

'''Holliday Junction TCGGTACCGA with Na and Ca Binding Sites.'''<br />

==Overview==

The role of metal ions in determining the solution conformation of the, Holliday junction is well established, but to date the picture of metal, ion binding from structural studies of the four-way DNA junction is very, incomplete. Here we present two refined structures of the Holliday, junction formed by the sequence d(TCGGTACCGA) in the presence of Na(+) and, Ca(2+), and separately with Sr(2+) to resolutions of 1.85A and 1.65A, respectively. This sequence includes the ACC core found to promote, spontaneous junction formation, but its structure has not previously been, reported. Almost complete hydration spheres can be defined for each metal, cation. The Na(+) sites, the most convincing observation of such sites in, junctions to date, are one on either face of the junction crossover, region, and stabilise the ordered hydration inside the junction arms. The, four Ca(2+) sites in the same structure are at the CG/CG steps in the, minor groove. The Sr(2+) ions occupy the TC/AG, GG/CC, and TA/TA sites in, the minor groove, giving ten positions forming two spines of ions, spiralling through the minor grooves within each arm of the stacked-X, structure. The two structures were solved in the two different C2 lattices, previously observed, with the Sr(2+) derivative crystallising in the more, highly symmetrical form with two-fold symmetry at its centre. Both, structures show an opening of the minor groove face of the junction of 8.4, degrees in the Ca(2+) and Na(+) containing structure, and 13.4 degrees in, the Sr(2+) containing structure. The crossover angles at the junction are, 39.3 degrees and 43.3 degrees, respectively. In addition to this, a, relative shift in the base pair stack alignment of the arms of 2.3A is, observed for the Sr(2+) containing structure only. Overall these results, provide an insight into the so-far elusive stabilising ion structure for, the DNA Holliday junction.

 

==About this Structure==

1L4J is a [http://en.wikipedia.org/wiki/Protein_complex Protein complex] structure of sequences from [http://en.wikipedia.org/wiki/ ] with CA and NA as [http://en.wikipedia.org/wiki/ligands ligands]. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1L4J OCA].

 

Conformational and hydration effects of site-selective sodium, calcium and strontium ion binding to the DNA Holliday junction structure d(TCGGTACCGA)(4)., Thorpe JH, Gale BC, Teixeira SC, Cardin CJ, J Mol Biol. 2003 Mar 14;327(1):97-109. PMID:[http://ispc.weizmann.ac.il//pmbin/getpm?pmid=12614611 12614611]

[[Category: Protein complex]]

[[Category: Cardin, C.J.]]

[[Category: Gale, B.C.]]

[[Category: Teixeira, S.C.M.]]

[[Category: Thorpe, J.H.]]

[[Category: CA]]

[[Category: NA]]

[[Category: holliday junction]]