Fig. 4: Model-based interpretation of the density of F(ab’)2 in subunit 2-5 based on the structure and flexibility of F(ab’)2 in subunit 1. | Nature Communications

Fig. 4: Model-based interpretation of the density of F(ab’)2 in subunit 2-5 based on the structure and flexibility of F(ab’)2 in subunit 1.

From: Cryomicroscopy reveals the structural basis for a flexible hinge motion in the immunoglobulin M pentamer

Fig. 4

a F(ab’)2 model rigidly translated from subunit 1 to subunit 4 (left panel), and in-plane pivoting of F(ab’)2 at the Cμ2/Cμ3 interface (right panel). b Left panel, side view of the left panel in (a). Right panel, out-of-plane pivoting of F(ab’)2 at Cμ2/Cμ3 interface. Red dots in (a, b) are the pivot point. c-e Upper panel, array of F(ab’)2 models with the in-plane and out-of-plane ranges of Cμ2 rotation at both \(\pm 50^\circ\) with \(10^\circ\) interval. The actual in-plane and out-of-plane directions are slightly tilted to match the tilted two-fold axes of the F(ab’)2 density (shown in Supplementary Fig. 6a–c). Lower panels, overlay of the experimental (pink) and simulated map (cyan) of F(ab’)2. Threshold level of the map is 0.025. (f, g) Cross-sections of the overlayed maps indicated by the dotted lines in (c) and (d). h Illustration of the overall structure of FL-IgM showing the two levels of flexibilities of F(ab’)2 among the five subunits.

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