title: Selective formation of ErbB-2/ErbB-3 heterodimers depends on the ErbB-3 affinity of epidermal growth factor-like ligands.
abstract: EGF-like growth factors activate their ErbB receptors by promoting receptor-mediated homodimerization or, alternatively, by the formation of heterodimers with the orphan ErbB-2 through an as yet unknown mechanism. To investigate the selectivity in dimer formation by ligands, we have applied the phage display approach to obtain ligands with modified C-terminal residues that discriminate between ErbB-2 and ErbB-3 as dimerization partners. We used the epidermal growth factor/transforming growth factor alpha chimera T1E as the template molecule because it binds to ErbB-3 homodimers with low affinity and to ErbB-2/ErbB-3 heterodimers with high affinity. Many phage variants were selected with enhanced binding affinity for ErbB-3 homodimers, indicating that C-terminal residues contribute to the interaction with ErbB-3. These variants were also potent ligands for ErbB-2/ErbB-3 heterodimers despite negative selection for such heterodimers. In contrast, phage variants positively selected for binding to ErbB-2/ErbB-3 heterodimers but negatively selected for binding to ErbB-3 homodimers can be considered as "second best" ErbB-3 binders, which require ErbB-2 heterodimerization for stable complex formation. Our findings imply that epidermal growth factor-like ligands bind ErbB-3 through a multi-domain interaction involving at least both linear endings of the ligand. Apparently the ErbB-3 affinity of a ligand determines whether it can form only ErbB-2/ErbB-3 complexes or also ErbB-3 homodimers. Because no separate binding domain for ErbB-2 could be identified, our data support a model in which ErbB heterodimerization occurs through a receptor-mediated mechanism and not through bivalent ligands.
authors.affiliation: University of Nijmegen, Department of Cell Biology, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands.
authors.forename: Catelijne
authors.initials: C
authors.lastname: Stortelers
authors.forename: Sebastian P
authors.initials: SP
authors.lastname: van der Woning
authors.forename: Saskia
authors.initials: S
authors.lastname: Jacobs-Oomen
authors.forename: Miriam
authors.initials: M
authors.lastname: Wingens
authors.forename: Everardus J J
authors.initials: EJ
authors.lastname: van Zoelen
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D010582:Bacteriophage lambda; D002478:Cells, Cultured; D003001:Cloning, Molecular; D019281:Dimerization; D004815:Epidermal Growth Factor / Q000378:metabolism*; D015723:Gene Library; D006412:Hematopoietic Stem Cells; D006801:Humans; D008024:Ligands; D008969:Molecular Sequence Data; D016296:Mutagenesis; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D020893:Receptor, ErbB-3 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*
chemical_list: D004815:Epidermal Growth Factor; D008024:Ligands; D018719:Erb-b2 Receptor Tyrosine Kinases; D020893:Receptor, ErbB-3