title: The receptor binding site of human interleukin-3 defined by mutagenesis and molecular modeling.
abstract: Interleukin-3 (IL-3) is a member of the cytokine superfamily that promotes multi-potential hematopoietic cell growth by interacting with a cell surface receptor composed of alpha and beta chains. The newly available three-dimensional structure of a variant of human (h) IL-3 allowed us to evaluate new and existing mutagenesis data and to rationally interpret the structure-function relationship of hIL-3 on a structural basis. The amino acid residues that were identified to be important for hIL-3 activity are grouped into two classes. The first class consists of largely hydrophobic residues required for the structural integrity of the protein, including the residues in IL-3 that are largely conserved among 10 mammalian species. These residues form the core of a scaffold for the second class of more rapidly diverging solvent-exposed residues, likely to be required for interaction with the receptor. Ten important and solvent-exposed residues, Asp21, Gly42, Glu43, Gln45, Asp46, Met49, Arg94, Pro96, Phe113, and Lys116, map to one side of the protein and form a putative binding site for the alpha subunit of the receptor. A model of the IL-3.IL-3 receptor complex based on the human growth hormone (hGH).hGH soluble receptor complex structure suggests that the interface between IL-3 and the IL-3 receptor alpha subunit consists of a cluster of hydrophobic residues flanked by electrostatic interactions. Although the IL-3/IL-3 receptor beta subunit interface cannot be uniquely located due to the lack of sufficient experimental data, several residues of the beta subunit that may interact with Glu22 of IL-3 are proposed. The role of these residues can be tested in future mutagenesis studies to define the interaction between IL-3 and IL-3 receptor beta subunit.
authors.affiliation: G. D. Searle and Company, St. Louis, Missouri 63198, USA.
authors.forename: B K
authors.initials: BK
authors.lastname: Klein
authors.forename: Y
authors.initials: Y
authors.lastname: Feng
authors.forename: C A
authors.initials: CA
authors.lastname: McWherter
authors.forename: W F
authors.initials: WF
authors.lastname: Hood
authors.forename: K
authors.initials: K
authors.lastname: Paik
authors.forename: J P
authors.initials: JP
authors.lastname: McKearn
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D006801:Humans; D007377:Interleukin-3 / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016296:Mutagenesis; D016185:Receptors, Interleukin-3 / Q000378:metabolism; D017386:Sequence Homology, Amino Acid
chemical_list: D007377:Interleukin-3; D016185:Receptors, Interleukin-3