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© 2009 by The American Society for Biochemistry and Molecular Biology, Inc.
The Intracellular Juxtamembrane Domain of the Epidermal Growth Factor (EGF) Receptor Is Responsible for the Allosteric Regulation of EGF Binding*
Jennifer L. Macdonald-Obermann, and Linda J. Pike1 Department of Biochemistry and Molecular Biophysics, Washington University School of Medicine, St. Louis, Missouri 63110 Abstract: We have previously shown that the binding of epidermal growth factor (EGF) to its receptor can best be described by a model that involves negative cooperativity in an aggregating system (Macdonald, J. L., and Pike, L. J. (2008) Proc. Natl. Acad. Sci. U. S. A. 105, 112–117). However, despite the fact that biochemical analyses indicate that EGF induces dimerization of its receptor, the binding data provided no evidence for positive linkage between EGF binding and dimer assembly. By analyzing the binding of EGF to a number of receptor mutants, we now report that in naive, unphosphorylated EGF receptors, ligand binding is positively linked to receptor dimerization but the linkage is abolished upon autophosphorylation of the receptor. Both phosphorylated and unphosphorylated EGF receptors exhibit negative cooperativity, indicating that mechanistically, cooperativity is distinct from the phenomenon of linkage. Nonetheless, both the positive linkage and the negative cooperativity observed in EGF binding require the presence of the intracellular juxtamembrane domain. This indicates the existence of inside-out signaling in the EGF receptor system. The intracellular juxtamembrane domain has previously been shown to be required for the activation of the EGF receptor tyrosine kinase (Thiel, K. W., and Carpenter, G. (2007) Proc. Natl. Acad. Sci. U. S. A. 104, 19238–19243). Our experiments expand the role of this domain to include the allosteric control of ligand binding by the extracellular domain.
Received for publication March 3, 2009. Revision received March 31, 2009. * This work was supported, in whole or in part, by National Institutes of Health Grants R01GM064491 and R01GM082824 (to L. J. P.).
1 To whom correspondence should be addressed: 660 So. Euclid Ave., Box 8231, St. Louis, MO 63110. Tel.: 314-362-9502; Fax: 314-362-7183; E-mail: pike{at}biochem.wustl.edu.
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Science Signaling. ISSN 1937-9145 (online), 1945-0877 (print). Pre-2008: Science's STKE. ISSN 1525-8882