1ob8: Difference between revisions

Two archaeal Holliday junction resolving enzymes, Holliday junction, cleavage (Hjc) and Holliday junction endonuclease (Hje), have been, characterized. Both are members of a nuclease superfamily that includes, the type II restriction enzymes, although their DNA cleaving activity is, highly specific for four-way junction structure and not nucleic acid, sequence. Despite 28% sequence identity, Hje and Hjc cleave junctions with, distinct cutting patterns--they cut different strands of a four-way, junction, at different distances from the junction centre. We report the, high-resolution crystal structure of Hje from Sulfolobus solfataricus. The, structure provides a basis to explain the differences in substrate, specificity of Hje and Hjc, which result from changes in dimer, organization, and suggests a viral origin for the Hje gene. Structural and, biochemical data support the modelling of an Hje:DNA junction complex, highlighting a flexible loop that interacts intimately with the junction, centre. A highly conserved serine residue on this loop is shown to be, essential for the enzyme's activity, suggesting a novel variation of the, nuclease active site. The loop may act as a conformational switch, ensuring that the active site is completed only on binding a four-way, junction, thus explaining the exquisite specificity of these enzymes.

1OB8 is a [http://en.wikipedia.org/wiki/Single_protein Single protein] structure of sequence from [http://en.wikipedia.org/wiki/Sulfolobus_solfataricus Sulfolobus solfataricus] with SO4 and EDO as [http://en.wikipedia.org/wiki/ligands ligands]. Structure known Active Site: SA1. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1OB8 OCA].  

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