Synchrotron SAXS data from solutions of the EspBS-K complex in 20 mM Tris-HCl, 300 mM NaCl, pH 8 were collected on the B21 beam line at the Diamond Light Source (Didcot, UK) using a Pilatus 2M detector at a sample-detector distance of 4.0 m and at a wavelength of λ = 0.1 nm (I(s) vs s, where s = 4πsinθ/λ, and 2θ is the scattering angle). In-line size-exclusion chromatography (SEC) SAS was employed. The SEC parameters were as follows: A 45.00 μl sample at 8.6 mg/ml was injected at a 0.08 ml/min flow rate onto a Shodex KW403 column at 20°C. 580 successive 3 second frames were collected. The data were normalized to the intensity of the transmitted beam and radially averaged; the scattering of the solvent-blank was subtracted.
The sample consists of a complex between EspB (small construct, amino acids 7–278) with the C-terminal region of EspK (amino acids 484–729). The SEC-eluted protein complex was directed through a 1.6-mm diameter quartz capillary cell held in vacuum.