A Cytokine–Cytokine Interaction in the Assembly of Higher-Order Structure and Activation of the Interleukine-3:Receptor Complex
Figure 1
Modeling of the IL-3:receptor complex.
(A) The structure of IL-3 (red) is superimposed on that of GM-CSF (yellow). The IL-3 receptor alpha chain domain 2 (α2, blue) is superimposed on the corresponding domain of GM-CSF receptor alpha chain (light magenta). The position of IL-3 receptor alpha chain domain 1 (α1, blue) is fitted as described in text. Domain 1 of one beta subunit (β1) and domain 4 of the other (β4′) are shown in green. The rest of the beta dimer is not shown. The three interfaces of the complex discussed in the text are labeled. The color scheme is used throughout the illustration unless otherwise indicated; (B) The resulting model of the IL-3:receptor complex after removing GM-CSF and its receptor alpha subunit, shown in ribbon covered with transparent surface; (c)sequence alignment of IL-3, GM-CSF and IL-5. Helices in IL-3 are indicated by horizontal bar in red. Residues discussed in the text are highlighted in different colors: green shade, residues interacting with the receptor β-subunit in IL-3 and GM-CSF; blue shade, residues of IL-3 that interact with the receptor α-subunit; magenta shade, residues of GM-CSF that interact with the receptor α-subunit; red font, functionally important residues from mutagenesis studies. Boxed residues are involved interface V interaction. Residue numbering above the sequence is for IL-3.