The N-terminus and C-terminus of IFN-gamma are binding domains for cloned soluble IFN-gamma receptor.
The mechanism of binding of murine IFN-gamma to its receptor has not been determined. We have studied this mechanism by examining the binding of overlapping synthetic peptides of IFN-gamma to cloned soluble murine IFN-gamma R. IFN-gamma (1-39) and IFN-gamma (95-133) were able to compete with [125I]IFN-gamma for binding to cloned soluble receptor. Peptides corresponding to the inner region of IFN-gamma--IFN-gamma (36-60), IFN-gamma (54-91), and IFN-gamma (78-107)--showed a markedly reduced ability to compete with [125I]IFN-gamma for receptor binding relative to the N-terminal and C-terminal peptides. In direct binding studies, the binding of [125I]-IFN-gamma (1-39) to soluble receptor could only be competed by IFN-gamma (1-39) and IFN-gamma and not by any of the other peptides including IFN-gamma (95-133). This suggests that the N- and C-termini of IFN-gamma bind to different regions of the receptor. These data in conjunction with previous structure/function studies and x-ray crystallographic data have allowed us to formulate a "velcro-key" model of IFN-gamma binding to receptor that involves both the N- and C-terminal domains. The N-terminus binds in the classical "lock-and-key" manner characterized by specific ligand-receptor binding. The hydrophilic C-terminus binds to a region of the receptor distinct from the N-terminus likely through the polycationic region, which is conserved across species barriers. Binding of this type would exhibit high affinity and low specificity similar to a piece of velcro. This interaction becomes specific when the C-terminus is in the context of the whole IFN-gamma molecule and may act to increase the affinity of receptor binding and/or facilitate signal transduction.
Griggs
N D
ND
Department of Microbiology and Cell Science, University of Florida, Gainesville 32611.
Jarpe
M A
MA
Pace
J L
JL
Russell
S W
SW
Johnson
H M
HM
D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D007371:Interferon-gamma / Q000378:metabolism*; D051379:Mice; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000378:metabolism; D011971:Receptors, Immunologic / Q000378:metabolism*; D017471:Receptors, Interferon; D012995:Solubility
D010446:Peptide Fragments; D011971:Receptors, Immunologic; D017471:Receptors, Interferon; D007371:Interferon-gamma