Figure 4. Structures of IR-3CS with insulin bound.

(A) 3D reconstructions of the 2:4 IR-3CS/insulin complexes in both asymmetric and symmetric conformations, and the corresponding ribbon representation. The asymmetric conformations 1 and 2 were fitted into cryo-EM at 4.5 Å and 4.9 Å resolution, respectively. The symmetric conformation was fitted into cryo-EM at 3.7 Å resolution. The asymmetric conformations 1 and 2 were reconstructed from 36% and 37% of the well-defined particles, respectively. The symmetric conformation was reconstructed from 27% of the well-defined particles. (B) Ribbon representations of the asymmetric and symmetric IR-3CS/insulin complexes. (C) Top view of the asymmetric IR-3CS/insulin complexes. The location of this interaction in the asymmetric dimer is indicated by gray boxes in B. (D) Superposition between the asymmetric conformations 1 (gray) and 2 (orange), revealing conformational change of the L1/CR domains (indicated by the arrow).

Figure 4—figure supplement 1. Cryo-EM analysis of the IR-3CS/insulin complex.

(A) A representative electron micrograph and 2D class averages of the IR-3CS/insulin complex. (B) Unsharpened cryo-EM map colored by local resolution. (C) The gold-standard Fourier shell correlation curve (FSC) for the cryo-EM map shown in Figure 4. (D) Flowchart of cryo-EM data processing.

Figure 4—figure supplement 2. Structural comparison between asymmetric IR-3CS and asymmetric IR-WT with subsaturated insulin bound.

(A) Asymmetric IR-3CS (conformation 1) and asymmetric IRs with subsaturated insulin bound (PDB: 7STJ, 7PG2, and 7MQS); gray. Insulin; orange. (B) Superposition between asymmetric IR-3CS (conformation 1, pink) and IR with subsaturated insulin bound (PDB: 7STJ, 7PG2, and 7MQS; green).