SAXS data analysis and modeling for (A) Fab-P and (B) Fab-R1. The Fab elbow angle versus χ score (upper), the SAXS profile fits and the residual plots (middle), and the best-scoring structural models (lower, red) are shown. The lowest χ scores were 1.30 for Fab-P and 1.65 for Fab-R1. In (A, lower), the x-ray crystal structure of Fab-P (green; PDB code 2HH0; χ = 1.79; elbow angle 128°) (58) was compared to the best-scoring model of Fab-P (red; χ = 1.30; elbow angle 177°). To see this figure in color, go online.