title: Identification of a ligand-binding site on the granulocyte colony-stimulating factor receptor by molecular modeling and mutagenesis.
abstract: Granulocyte colony-stimulating factor (G-CSF) initiates its effects on cells of the neutrophil lineage by inducing formation of a homodimeric receptor complex. The structure of the G-CSF receptor has not yet been determined, therefore we used molecular modeling to identify regions of the receptor that were likely to be involved in ligand binding. The G-CSF receptor sequence was aligned with all the available sequences of the gp130 and growth hormone receptor families and a model of the cytokine receptor homologous domain was constructed, based on the growth hormone receptor structure. Alanine substitution mutagenesis was performed on loops and individual residues that were predicted to bind ligand. Mutant receptors were expressed in factor-dependent Ba/F3 cells and assessed for proliferation response and ligand binding. Six residues were identified that significantly reduced receptor function, with Arg288 in the F'-G' loop having the greatest effect. These residues formed a binding face on the receptor model resembling the growth hormone receptor site, which suggests that the model is reasonable. However, electrostatic analysis of the model provided further evidence that the mechanism of receptor dimerization is different from that of the growth hormone receptor.
authors.affiliation: Ludwig Institute for Cancer Research, Melbourne Tumour Biology Branch, P. O. Box 2008, Royal Melbourne Hospital, Parkville, Australia 3050. judy.layton@ludwig.edu.au
authors.forename: J E
authors.initials: JE
authors.lastname: Layton
authors.forename: J
authors.initials: J
authors.lastname: Iaria
authors.forename: D K
authors.initials: DK
authors.lastname: Smith
authors.forename: H R
authors.initials: HR
authors.lastname: Treutlein
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D003346:Corticotropin-Releasing Hormone / Q000378:metabolism; D005434:Flow Cytometry; D008024:Ligands; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D016188:Receptors, Granulocyte Colony-Stimulating Factor / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment; D055672:Static Electricity; D014407:Tumor Cells, Cultured
chemical_list: D008024:Ligands; D016188:Receptors, Granulocyte Colony-Stimulating Factor; D003346:Corticotropin-Releasing Hormone