A cytokine-cytokine interaction in the assembly of higher-order structure and activation of the interleukine-3:receptor complex.
Interleukine-3 (IL-3) binds its receptor and initiates a cascade of signaling processes that regulate the proliferation and differentiation of hematopoietic cells. To understand the detailed mechanisms of IL-3 induced receptor activation, we generated a homology model of the IL-3:receptor complex based on the closely related crystal structure of the GM-CSF:receptor complex. Model-predicted interactions between IL-3 and its receptor are in excellent agreement with mutagenesis data, which validate the model and establish a detailed view of IL-3:receptor interaction. The homology structure reveals an IL-3:IL-3 interaction interface in a higher-order complex modeled after the dodecamer of the GM-CSF:receptor complex wherein an analogous GM-CSF:GM-CSF interface is also identified. This interface is mediated by a proline-rich hydrophobic motif (PPLPLL) of the AA' loop that is highly exposed in the structure of isolated IL-3. Various experimental data suggest that this motif is required for IL-3 function through receptor-binding independent mechanisms. These observations are consistent with structure-function studies of the GM-CSF:receptor complex showing that formation of the higher-order cytokine:receptor complex is required for signaling. However, a key question not answered from previous studies is how cytokine binding facilitates the assembly of the higher-order complex. Our studies here reveal a potential cytokine-cytokine interaction that participates in the assembly of the dodecamer complex, thus linking cytokine binding to receptor activation.
Dey
Raja
R
Department of Biological Sciences, Molecular and Computational Biology, University of Southern California, Los Angeles, California, United States of America.
Ji
Kunmei
K
Liu
Zhigang
Z
Chen
Lin
L
D000595:Amino Acid Sequence; D016207:Cytokines / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011485:Protein Binding; D011487:Protein Conformation; D016185:Receptors, Interleukin-3 / Q000737:chemistry / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
D016207:Cytokines; D016185:Receptors, Interleukin-3