Arnon, Tal I. and Kaiser, Jens T. and West, Anthony P., Jr. and Olson, Rich and Diskin, Ron and Viertlboeck, Birgit C. and Göbel, Thomas W. and Bjorkman, Pamela J. (2008) The Crystal Structure of CHIR-AB1: A Primordial Avian Classical Fc Receptor. Journal of Molecular Biology, 381 (4). pp. 1012-1024. ISSN 0022-2836 http://resolver.caltech.edu/CaltechAUTHORS:ARNjmb08
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CHIR-AB1 is a newly identified avian immunoglobulin (Ig) receptor that includes both activating and inhibitory motifs and was therefore classified as a potentially bifunctional receptor. Recently, CHIR-AB1 was shown to bind the Fc region of chicken IgY and to induce calcium mobilization via association with the common γ-chain, a subunit that transmits signals upon ligation of many different immunoreceptors. Here we describe the 1.8-Å-resolution crystal structure of the CHIR-AB1 ectodomain. The receptor ectodomain consists of a single C2-type Ig domain resembling the Ig-like domains found in mammalian Fc receptors such as FcγRs and FcαRI. Unlike these receptors and other monomeric Ig superfamily members, CHIR-AB1 crystallized as a 2-fold symmetrical homodimer that bears no resemblance to variable or constant region dimers in an antibody. Analytical ultracentrifugation demonstrated that CHIR-AB1 exists as a mixture of monomers and dimers in solution, and equilibrium gel filtration revealed a 2:1 receptor/ligand binding stoichiometry. Measurement of the 1:1 CHIR-AB1/IgY interaction affinity indicates a relatively low affinity complex, but a 2:1 CHIR-AB1/IgY interaction allows an increase in apparent affinity due to avidity effects when the receptor is tethered to a surface. Taken together, these results add to the structural understanding of Fc receptors and their functional mechanisms.
|Additional Information:||Copyright © 2008 Elsevier. Received 23 April 2008; received in revised form 25 June 2008; accepted 26 June 2008. Available online 3 July 2008. his work was supported by a Jane Coffin Child's Memorial Fund Fellowship for Medical Research (T.I.A.), the National Institutes of Health (2 R37 AI041239-06A1 to P.J.B.), the Beckman Institute at Caltech (R.O.), funds from the Gordon and Betty Moore Foundation in support of the Molecular Observatory at Caltech, and a Deutsche Forschungsgemeinschaft grant GO489/3-6 (T.W.G.). Atomic coordinates have been deposited in the Protein Data Bank with accession code 2VSD. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.jmb.2008.06.082|
|Subject Keywords:||Fc receptor; crystal structure; dimer; chicken; bifunctional receptor|
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|Deposited By:||Archive Administrator|
|Deposited On:||29 Sep 2008 22:26|
|Last Modified:||26 Dec 2012 10:20|
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