Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 103, Issue 15, Pages 5735-5740Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0601469103
Keywords
cell signaling; growth factors; ligand binding; mathematical modeling; surface receptors
Categories
Funding
- NCI NIH HHS [R01-CA096768, R01 CA079992, R01 CA079992-09, R01 CA096768] Funding Source: Medline
- NIAMS NIH HHS [R01 AR051448, R01-AR051886, R01-AR051448, R01 AR051886] Funding Source: Medline
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The small subpopulation of high-affinity EGF receptors (EGFRs) on living cells revealed by Scatchard analysis of 125I-EGF binding results was discovered nearly three decades ago, yet not much is known about the underlying mechanism. After the determination of the structure of different forms of EGFR extracellular domain it was proposed that the monomeric tethered configuration corresponds to the majority of low-affinity receptors, whereas the extended dimeric configuration corresponds to the minority of the high-affinity class of EGFRs. Mathematical modeling of EGF-binding experiments to different conformational mutants of EGFR has shown that the high-affinity class of EGFR on living cells does not correspond to the extended configuration of EGFR and can only be accounted for by including in the mathematical model an additional binding event that is attributed to the dynamic nature of EGFR on living cells. To circumvent this problem we have performed similar experiments in the background of an EGFR mutant that does not form high-affinity sites. Quantitative analysis and mathematical modeling of these data show that release of the intramolecular tether causes a 2-fold increase in EGF-binding affinity, whereas elimination of the dimerization arm reduces EGF-binding affinity by approximate to 6-fold. These experiments confirm the salient features of the structural model for EGFR regulation and argue further that the intramolecular tether provides only limited autoinhibitory control of EGFR activity and that the low-affinity class of EGF-binding sites on living cells reflects interconverting, tethered, and extended receptor configurations.
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