SAXS analysis of empty nanodisc. (A) Kratky plot analysis. (B) Scattering curves for experimental data (red) and theoretical curves of starting model (dashed line, χ² = 3.64) and refined model (solid line, χ² = 0.26). (C) Pairwise distribution function. Inset depicts experimental data (red) and an indirect Fourier transform of the P(r) distribution plot (black), showing strong agreement between both sets of data. (D) (Left) An ab initio molecular envelope. (Right) Modeled empty nanodisc in sphere representation (scaffold protein: red, lipids: light orange) fit into the SAXS-derived molecular envelope.