The Asn-420-linked sugar chain in human epidermal growth factor receptor suppresses ligand-independent spontaneous oligomerization. Possible role of a specific sugar chain in controllable receptor activation.
To elucidate a role(s) of Asn-linked sugar chain(s) in the function of epidermal growth factor receptor (EGFR), a series of the EGFR mutants were prepared in which potential glycosylation sites in the domain III were eliminated by site-directed mutagenesis. Although the wild-type and mutants of Asn-328, Asn-337, and Asn-389 underwent autophosphorylation in response to epidermal growth factor (EGF), the Asn-420 --> Gln mutant was found to be constitutively tyrosine-phosphorylated. This abnormal ligand-independent phosphorylation of the mutant appears to be due to a ligand-independent spontaneous oligomer formation, as shown by a cross-linking experiment using the purified soluble extracellular domain (sEGFR). As revealed by the dissociation of the Asn-420 --> Gln sEGFR oligomer by simple dilution, it seems likely that the equilibrium is shifted toward oligomer formation to an unusual degree. Furthermore, it was also found that the mutation caused a loss of the ability to bind EGF. These findings suggest that the sugar chain linked to Asn-420 plays a crucial role in EGF binding and prevents spontaneous oligomerization of the EGFR, which may otherwise lead to uncontrollable receptor activation, and support the view of a specific role of an Asn-linked sugar chain in the function of a glycoprotein.
Tsuda
T
T
Department of Biochemistry, Osaka University Medical School, 2-2 Yamadaoka, Suita, Osaka 565-0871, Japan.
Ikeda
Y
Y
Taniguchi
N
N
D001216:Asparagine; D019281:Dimerization; D066246:ErbB Receptors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008024:Ligands; D016297:Mutagenesis, Site-Directed; D015398:Signal Transduction
D008024:Ligands; D001216:Asparagine; D066246:ErbB Receptors