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Zn-α_2-glycoprotein, an MHC Class I-Related Glycoprotein Regulator of Adipose Tissues: Modification or Abrogation of Ligand Binding by Site-Directed Mutagenesis

McDermott, Lindsay C. and Freel, June A. and West, Anthony P. and Bjorkman, Pamela J. and Kennedy, Malcolm W. (2006) Zn-α_2-glycoprotein, an MHC Class I-Related Glycoprotein Regulator of Adipose Tissues: Modification or Abrogation of Ligand Binding by Site-Directed Mutagenesis. Biochemistry, 45 (7). pp. 2035-2041. ISSN 0006-2960. https://resolver.caltech.edu/CaltechAUTHORS:20170131-090555687

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Abstract

Zn-α_2-glycoprotein (ZAG) is a soluble lipid-mobilizing factor associated with cancer cachexia and is a novel adipokine. Its X-ray crystal structure reveals a poly(ethylene glycol) molecule, presumably substituting for a higher affinity natural ligand, occupying an apolar groove between its α1 and α2 domain helices that corresponds to the peptide binding groove in class I MHC proteins. We previously provided evidence that the groove is a binding site for hydrophobic ligands that may relate to the protein's signaling function and that the natural ligands are probably (polyunsaturated) fatty acid-like. Using fluorescence-based binding assays and site-directed mutagenesis, we now demonstrate formally that the groove is indeed the binding site for hydrophobic ligands. We also identify amino acid positions that are involved in ligand binding and those that control the shape and exposure to solvent of the binding site itself. Some of the mutants showed minimal effects on their binding potential, one showed enhanced binding, and several were completely nonbinding. Particularly notable is Arg-73, which projects into one end of the binding groove and is the sole charged amino acid adjacent to the ligand. Replacing this amino acid with alanine abolished ligand binding and closed the groove to solvent. Arg-73 may therefore have an unexpected dual role in binding site access and anchor for an amphiphilic ligand. These data add weight to the distinctiveness of ZAG among MHC class I-like proteins in addition to providing defined binding-altered mutants for cellular signaling studies and potential medical applications.


Item Type:Article
Related URLs:
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http://dx.doi.org/10.1021/bi051881vDOIArticle
http://pubs.acs.org/doi/full/10.1021/bi051881vPublisherArticle
ORCID:
AuthorORCID
Bjorkman, Pamela J.0000-0002-2277-3990
Additional Information:© 2006 American Chemical Society. Received 15 September 2005. Published online 31 January 2006. Published in print 1 February 2006. This work was supported by grants from the Wellcome Trust (United Kingdom) to M.W.K. We are indebted to Alan Cooper for insightful advice and discussions and to Thomas Jess, Sharon Kelly, and Nick Price for invaluable help in the CD analysis.
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Funding AgencyGrant Number
Wellcome TrustUNSPECIFIED
Issue or Number:7
Record Number:CaltechAUTHORS:20170131-090555687
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20170131-090555687
Official Citation:Zn-α2-glycoprotein, an MHC Class I-Related Glycoprotein Regulator of Adipose Tissues:  Modification or Abrogation of Ligand Binding by Site-Directed Mutagenesis Lindsay C. McDermott, June A. Freel, Anthony P. West, Pamela J. Bjorkman, and Malcolm W. Kennedy Biochemistry 2006 45 (7), 2035-2041 DOI: 10.1021/bi051881v
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:73860
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:31 Jan 2017 17:21
Last Modified:03 Oct 2019 16:32

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