Synapses and branching forks
Scott Williams and Gabriel Moncalian of the Scripps Institute's Department of Molecular Biology and the Skaggs Institute for Chemical Biology crystallized and determined x-ray crystal structures of key domains of P. furiosus Mre11 bound to DNA in two configurations, representing two kinds of DSB-repair interactions.
At beamline 12.3.1 at Berkeley Lab's Advanced Light Source, known as SIBYLS ("Structurally Integrated BiologY for Life Sciences"), the researchers performed both high-resolution protein crystallography and small-angle x-ray scattering (SAXS), which can image proteins and complexes in aqueous solution, closer to their natural state.
"Like breaking a piece of wood into two parts, the severed termini of the DNA in a double-strand break have ends of varying shape," says Williams. "The high-resolution snapshots we obtained of Mre11 binding to different DNA end-structures show how the Mre11 protein has evolved to hone in on and sense these variable mutagenic lesions."
Of the two complexes that were crystallized, the "synaptic complex" bound the ends of a pair of DNA helices in orientations mimicking the kind of break that might result when a double strand of DNA is severed by radiation or chemical damage.
A different form of double-strand break is also common and occurs when a DNA helix is forking or "unzipping" during replication; if the process is interrupted, the fork may collapse. This "branched complex" of DNA bound with Mre11 involves different topography and interactions than the synaptic complex.
|Contact: Paul Preuss|
DOE/Lawrence Berkeley National Laboratory