Fig. 2.

Structural homology of the DC-SIGN/IgG1 Fc and the CD23/IgE Fc complex. (A) Structure-based sequence alignment of human DC-SIGN and IgG1-Fc to the CD23/IgE-Fc complex. The amino acid residues depicted in the one-letter code are colored according to their property (i.e., acidic residues in red, basic in blue, hydrophobic in green). Cysteine residues, all involved in disulfide bridges, are depicted in gray. The interactions between the complex partners are indicated by black lines connecting the involved residues with salt bridges relevant for the CD23/IgE-Fc complex shown in red (7). Hydrogen bonds between IgG and DC-SIGN or CD23 are shown in blue and green lines, respectively. (B) Model of the DC-SIGN/sFc complex. The protein main chains are represented as tubes. The CD23/IgE-Fc complex [thin gray tube, Protein Data Bank (PDB) code 4EZM] is overlaid with the model of the IgG Fc fragment (red and blue) in complex with DC-SIGN (magenta and green). Disulfide bridges and the carbohydrate moiety associated to the Fc fragment are shown as sticks. The square depicts the region shown in detail in C. The generation of the model is described in the supplementary materials. (C) Detailed interaction of DC-SIGN and CD23 with hIgG1-Fc. A close-up of some of the residues expected to be involved in the DC-SIGN/IgG1-Fc (Left) and CD23/IgG1-Fc complex (Right), respectively. The depicted clipping of the complex model is indicated in B.