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X-ray synchrotron radiation scattering data from the Ag43a alpha domain from E. Coli in 25 mM HEPES 150 mM NaCl, pH 7.0 were collected on the SAXS/WAXS beam line of the Australian Synchrotron (Melbourne, Australia) using a 2D Photon counting Pilatus 1M-W pixel detector (s = 4π sin θ/λ, where 2θ is the scattering angle). Fourteen successive 1 second frames were collected at 1.2 mg/ml. The data were normalized to the intensity of the transmitted beam and radially averaged and the scattering of the solvent-blank was subtracted. The solution is a mixture of different oligomeric states, and a monomer-dimer mixture was fit to the data. The modelling involved taking the monomer and dimer from the crystal structure (PDB ID 4KH3), and generating the scattering profiles for each in Crysol. The relative proportions of each and a constant background correction were optimised by minimising χ2 using the Solver function in Excel. Approximately 67% of the protein was determined to be in the monomeric state and 33% in the dimeric state, with χ2 = 18.8. The model reproduces the features of the curve, but the small systematic deviations are likely due to the presence of small amounts of higher order oligomers.
Concentration = UNKNOWN
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s, nm-1
