Fig. 2: Domain movements and elbow regions in dimeric Fabs.
a (left) Comparison of H chain conformations in unbound monomeric Fab CBH7 (magenta), E2-bound HC84.26.5D (yellow), and E2-bound CBH4B (green). The switch peptide linking VH and CH1 is blue. H chains were superposed through their VH domains. Angles of rotation around the switch peptide with respect to Fab CBH7 are indicated. (right) Comparison of L chain conformations in unbound monomeric Fab CBH7 (magenta), E2-bound HC84.26.5D (yellow), and E2-bound CBH4B (green). The switch peptide linking VL and CL is blue. L chains were superposed through their VL domains. Angles of rotation around the switch peptide with respect to Fab CBH7 are indicated. b (top) Crystal structure of monomeric Fab CBH7 with elbow region between VH and CH1 domains framed in black. The elbow angle is 133°. The elbow region between VL and CL domains is framed in red. (middle) Close-up view of standard ball-and-socket joint between VH and CH1 in Fab CBH7 formed by VH residues Val11, Thr110, and Ser112 (socket) and CH1 residues Phe145 and Pro146 (ball). (bottom) Close-up view of residues forming the elbow region between VL and CL. c (top) Cryo-EM structure of Fab HC84.26.5D in the complex with E2 (not shown) with elbow region between VH and CH1 framed in black. The elbow angle is 202°. The elbow region between VL and CL domains is framed in red. (middle) Close-up view of residues forming ball-and-socket joint in Fab CBH7 but rearranged in the Fab HC84.26.5D–E2 complex. (bottom) Close-up view of residues forming the elbow region between VL and CL. d (top) Cryo-EM structure of Fab CBH4B in the complex with E2 (not shown) with elbow region between VH and CH1 framed in black. The elbow angle is 215°. The elbow region between VL and CL domains is framed in red. (middle) Close-up view of residues forming ball-and-socket joint in Fab CBH7 but rearranged in the Fab CBH4B–E2 complex. (bottom) Close-up view of residues forming the elbow region between VL and CL.
