Identification of the high affinity receptor binding region in human immunoglobulin E.
We have investigated the capacity of N- and C-terminally truncated and chimeric human (h) IgE-derived peptides to inhibit the binding of 125I-labeled hIgE, and to engage cell lines expressing high and low affinity receptors (Fc-epsilon-RI/II). The peptide sequence Pro343-Ser353 of the hC-epsilon-3 domain is common to all h-epsilon-chain peptides that recognize hFc-epsilon-RI. This region in IgE is homologous to the A loop in C-gamma-2 that engages the rat neonatal IgG receptor. Optimum Fc-epsilon-RI occupancy by hIgE occurs at pH 6.4, with a second peak at 7.4. N- or C-terminal truncation has little effect on the association rate of the ligands with this receptor. Dissociation markedly increases following C-terminal deletion, and hFc-epsilon-RI occupancy at pH 6.4 is diminished. His residue(s) in the C-terminal region of the epsilon-chain may thus contribute to the high affinity of interaction. Grafting the homologus rat epsilon-chain sequence into hIgE maintains hFc-epsilon-RI interaction without conferring binding to rat Fc-epsilon-RI. hFc-epsilon-RII interaction is lost, suggesting that these residues also contribute to hFc-epsilon RII binding. h-epsilon-chain peptides comprising only this sequence do not block hIgE/hFc-epsilon-RI interaction or engage the receptor. Therefore, sequences N- or C-terminal to this core peptide provide structures necessary for receptor recognition.
Helm
B A
BA
Krebs Institute for Biomolecular Research, University of Sheffield, United Kingdom.
Sayers
I
I
Higginbottom
A
A
Machado
D C
DC
Ling
Y
Y
Ahmad
K
K
Padlan
E A
EA
Wilson
A P
AP
D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D002460:Cell Line; D003001:Cloning, Molecular; D017931:DNA Primers; D004926:Escherichia coli; D005982:Glutathione Transferase / Q000096:biosynthesis; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007073:Immunoglobulin E / Q000737:chemistry* / Q000378:metabolism*; D007140:Immunoglobulin Fab Fragments / Q000737:chemistry; D007139:Immunoglobulin epsilon-Chains / Q000096:biosynthesis / Q000737:chemistry* / Q000378:metabolism*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016296:Mutagenesis; D016297:Mutagenesis, Site-Directed; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D011487:Protein Conformation; D051381:Rats; D017455:Receptors, IgE / Q000096:biosynthesis / Q000378:metabolism*; D017452:Receptors, IgG / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000378:metabolism; D015183:Restriction Mapping; D017384:Sequence Deletion
D017931:DNA Primers; D007140:Immunoglobulin Fab Fragments; D007139:Immunoglobulin epsilon-Chains; D017455:Receptors, IgE; D017452:Receptors, IgG; D011993:Recombinant Fusion Proteins; D007073:Immunoglobulin E; D005982:Glutathione Transferase