The transmembrane domains of ErbB receptors do not dimerize strongly in micelles.
The epidermal growth factor receptors (erbB) constitute an important class of single pass transmembrane receptors involved in the transduction of signals important for cell proliferation and differentiation. Receptor association is a key event in the signal transduction process, but the molecular basis of this interaction is not fully understood. Previous biochemical and genetic studies have suggested that the single transmembrane helices of these receptor proteins might play a role in stabilizing the receptor complexes. To determine if the erbB transmembrane domains could provide a driving force to stabilize the receptor dimers, we carried out a thermodynamic study of these domains expressed as C-terminal fusion proteins with staphylococcal nuclease. Similar fusion constructs have been used successfully to investigate the oligomerization and association thermodynamics of a number of transmembrane sequences, including that of glycophorin A. Using SDS-PAGE analysis and sedimentation equilibrium analytical ultracentrifugation, we do not find strong, specific homo or hetero-interactions between the transmembrane domains of the erbB receptors in micellar solutions. Our results indicate that any preferential interactions between these domains in micellar solutions are extremely modest, of the order of 1 kcal mol(-1) or less. We applied a thermodynamic formalism to assess the effect of weakly interacting TM segments on the behavior of a covalently attached soluble domain. In the case of the ligand-bound EGFR ectodomain, we find that restriction of the ectodomain to the micellar phase by a hydrophobic TM, even in the absence of strong specific interactions, is largely sufficient to account for the previously reported increase in dimerization affinity.
Stanley
Ann Marie
AM
T.C. Jenkins Department of Biophysics, Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21218, USA.
Fleming
Karen G
KG
D000595:Amino Acid Sequence; D002462:Cell Membrane / Q000378:metabolism*; D019281:Dimerization; D066246:ErbB Receptors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D008823:Micelles; D008836:Micrococcal Nuclease / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D011485:Protein Binding / Q000187:drug effects; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012967:Sodium Dodecyl Sulfate / Q000737:chemistry / Q000494:pharmacology
D008823:Micelles; D011993:Recombinant Fusion Proteins; D012967:Sodium Dodecyl Sulfate; D066246:ErbB Receptors; D008836:Micrococcal Nuclease