The scattering pattern of the N TAILHN -XD complex was obtained following this process: to avoid any possible bias on the absolute intensities due to the concentration, the experimental merged scattering curves obtained as described above were normalized by their theoretical I(0). The scattering pattern of XD was then subtracted twice from the scattering pattern of the mixture N TAILHN -XD (molar ratio 1:2). Given the rather low K D between N TAIL and XD ($100 nM; see Results section), we assumed that the concentration of uncomplexed N TAILHN in solution is negligible at the concentration used in the SAXS experiments (2 to 10 mg/mL). The scattering pattern of the complex thus obtained was then used for further calculations.