Interaction of the Low-Affinity Receptor CD23/FcRII Lectin Domain with the Fc
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- 作者：Jianguo Shi ; Rodolfo Ghirlando ; Rebecca L. Beavil ; Andrew J. Beavil ; Maura B. Keown ; Robert J. Young ; Raymond J. Owens ; Brian J. Sutton ; and Hannah J. Gould
- 刊名：Biochemistry
- 出版年：1997
- 出版时间：February 25, 1997
- 年：1997
- 卷：36
- 期：8
- 页码：2112 - 2122
- 全文大小：318K
- 年卷期：v.36,no.8(February 25, 1997)
- ISSN：1520-4995
文摘
CD23/Fc
RII, the low-affinity receptor for IgE, is amultifunctional protein of importance inblood cell development and the immune system. We have studied theinteraction of CD23 with IgE insolution using hydrodynamic methods applied to recombinant fragments ofboth ligands: sCD23,corresponding to the soluble lectin domain of CD23, and Fc3-4, adimer of the C3-C4 sequence ofIgE. The hydrodynamic, spectroscopic, and biological properties ofthese fragments suggest that theyhave a fully native structure. Sedimentation equilibrium studieson mixtures of sCD23 and Fc3-4 indicatethat IgE has two binding sites for CD23, each characterized byaffinities of approximately 105M-1.Analysis of the sedimentation as a function of temperature allowsconclusions to be drawn about thethermodynamics of binding at the two sites. Binding at the firstsite is characterized by large changes inenthalpy(
H
To = -2.1 ± 3.3 kcal mol-1) and heatcapacity (Cp = -320 ± 320 calmol-1K-1),whereas binding at the second site is characterized by small changes inenthalpy(HTo = 0.1 ± 5.6 kcalmol-1) and heat capacity (Cp= -140 ± 550 cal mol-1K-1). In native CD23, there are two orthreelectin domains, associated through an 
-helical coiled-coil stalk.The predicted structure of the CD23oligomers and symmetry considerations rule out the possibility of twolectin domains from one oligomerbinding to identical sites in IgE. The notion of two types ofinteraction in the 2:1 complex betweenCD23 and IgE is consistent with the thermodynamic datapresented.
RII, the low-affinity receptor for IgE, is amultifunctional protein of importance inblood cell development and the immune system. We have studied theinteraction of CD23 with IgE insolution using hydrodynamic methods applied to recombinant fragments ofboth ligands: sCD23,corresponding to the soluble lectin domain of CD23, and Fc3-4, adimer of the C3-C4 sequence ofIgE. The hydrodynamic, spectroscopic, and biological properties ofthese fragments suggest that theyhave a fully native structure. Sedimentation equilibrium studieson mixtures of sCD23 and Fc3-4 indicatethat IgE has two binding sites for CD23, each characterized byaffinities of approximately 105M-1.Analysis of the sedimentation as a function of temperature allowsconclusions to be drawn about thethermodynamics of binding at the two sites. Binding at the firstsite is characterized by large changes inenthalpy(HTCp = -320 ± 320 calmol-1K-1),whereas binding at the second site is characterized by small changes inenthalpy(HTCp= -140 ± 550 cal mol-1K-1). In native CD23, there are two orthreelectin domains, associated through an -helical coiled-coil stalk.The predicted structure of the CD23oligomers and symmetry considerations rule out the possibility of twolectin domains from one oligomerbinding to identical sites in IgE. The notion of two types ofinteraction in the 2:1 complex betweenCD23 and IgE is consistent with the thermodynamic datapresented.