title: A monomeric chicken IgY receptor binds IgY with 2:1 stoichiometry.
abstract: IgY is the principal serum antibody in birds and reptiles, and an IgY-like molecule was the evolutionary precursor of both mammalian IgG and IgE. A receptor for IgY on chicken monocytes, chicken leukocyte receptor AB1 (CHIR-AB1), lies in the avian leukocyte receptor cluster rather than the classical Fc receptor cluster where the genes for mammalian IgE and IgG receptors are found. IgG and IgE receptors bind to the lower hinge region of their respective antibodies with 1:1 stoichiometry, whereas the myeloid receptor for IgA, FcalphaRI, and the IgG homeostasis receptor, FcRn, which are found in the mammalian leukocyte receptor cluster, bind with 2:1 stoichiometry between the heavy chain constant domains 2 and 3 of each heavy chain. In this paper, the extracellular domain of CHIR-AB1 was expressed in a soluble form and shown to be a monomer that binds to IgY-Fc with 2:1 stoichiometry. The two binding sites have similar affinities: K(a)(1) = 7.22 +/- 0.22 x 10(5) m(-1) and K(a)(2) = 3.63 +/- 1.03 x 10(6) m(-1) (comparable with the values reported for IgA binding to its receptor). The affinity constants for IgY and IgY-Fc binding to immobilized CHIR-AB1 are 9.07 +/- 0.07 x 10(7) and 6.11 +/- 0.02 x 10(8) m(-1), respectively, in agreement with values obtained for IgY binding to chicken monocyte cells and comparable with reported values for human IgA binding to neutrophils. Although the binding site for CHIR-AB1 on IgY is not known, the data reported here with a monomeric receptor binding to IgY at two sites with low affinity suggest an IgA-like interaction.
authors: From the Randall Division of Cell and Molecular Biophysics, King's College London, New Hunt's House, Guy's Campus, London SE1 1UL, United Kingdom.
authors: Alexander I
authors: AI
authors: Taylor
authors: Rebecca L
authors: RL
authors: Beavil
authors: Brian J
authors: BJ
authors: Sutton
authors: Rosaleen A
authors: RA
authors: Calvert
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000502:physiology; D002460:Cell Line; D002645:Chickens; D006801:Humans; D007073:Immunoglobulin E / Q000737:chemistry / Q000378:metabolism; D007074:Immunoglobulin G / Q000737:chemistry / Q000378:metabolism; D007143:Immunoglobulin Heavy Chains / Q000737:chemistry* / Q000378:metabolism; D007136:Immunoglobulins / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000502:physiology; D011961:Receptors, Fc / Q000737:chemistry* / Q000378:metabolism
chemical_list: C016512:IgY; D007074:Immunoglobulin G; D007143:Immunoglobulin Heavy Chains; D007136:Immunoglobulins; D011961:Receptors, Fc; D007073:Immunoglobulin E