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Zn-alpha2-glycoprotein, an MHC class I-related glycoprotein regulator of adipose tissues: modification or abrogation of ligand binding by site-directed mutagenesis

  • Lindsay McDermott
    ,
  • June A. Freel
    ,
  • Anthony P. West
    ,
  • Pamela J. Bjorkman
    ,
  • Malcolm W. Kennedy
Research Output: Contribution to journal Article Peer-review

Sustainable Development Goals

  • SDG 3 - Good Health and Well-being
    SDG 3 Good Health and Well

Abstract

Zn-alpha(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 alpha(1) and alpha(2) 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.

Publication Information

Output type

Research Output: Contribution to journal Article Peer-review

Original language

English

Pages from-to (Number of pages)

Pages 2035-41

Journal (Volume, Issue Number)

Biochemistry (Volume 45, Issue 7)

Publication milestones

  • Published - 31/01/2006

Publication status

Published - 31/01/2006

ISSN

0006-2960

External Publication IDs

  • handle.net: 10547/622682
  • Scopus: 33144460013

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