Hydrophobic ligand binding by Zn-alpha(2)-glycoprotein, a soluble fat-depleting factor related to major histocompatibility complex proteins

Kennedy, M.W., Heikema, A.P., Cooper, A., Bjorkman, P.J. and Sanchez, L.M. (2001) Hydrophobic ligand binding by Zn-alpha(2)-glycoprotein, a soluble fat-depleting factor related to major histocompatibility complex proteins. Journal of Biological Chemistry, 276(37), pp. 35008-35013. (doi:10.1074/jbc.C100301200)

Full text not currently available from Enlighten.

Publisher's URL: http://dx.doi.org/10.1074/jbc.C100301200

Abstract

Zn-alpha (2)-glycoprotein (ZAG) is a member of the major histocompatibility complex (MHC) class I family of proteins and is identical in amino acid sequence to a tumor-derived lipid- mobilizing factor associated with cachexia in cancer patients. ZAG is present in plasma and other body fluids, and its natural function, like leptin's, probably lies in lipid store homeostasis. X-ray crystallography has revealed an open groove between the helices of ZAG's alpha (1). and alpha (2) domains, containing an unidentified small ligand in a position similar to that of peptides in MHC proteins (Sanchez, L. M., Chirino, A. J., and Bjorkman, P. J. (1999) Science 283,1914-1919). Here we show, using serum-derived and bacterial recombinant protein, that ZAG binds the fluorophore-tagged fatty acid 11- (dansylamino)undecanoic acid (DAUDA) and, by competition, natural fatty acids such as arachidonic, linolenic, eicosapentaenoic, and docosahexaenoic acids. Other MHC class I- related proteins (FcRn, HFE, HLA-Cw*0702) showed no such evidence of binding. Fluorescence and isothermal calorimetry analysis showed that ZAG binds DAUDA with K-d in the micromolar range, and differential scanning calorimetry showed that ligand binding increases the thermal stability of the protein. Addition of fatty acids to ZAG alters its intrinsic (tryptophan) fluorescence emission spectrum, providing a strong indication that ligand binds in the expected position close to a cluster of exposed tryptophan side chains in the groove. This study therefore shows that ZAG binds small hydrophobic ligands, that the natural ligand may be a polyunsaturated fatty acid, and provides a fluorescence-based method for investigating ZAG- ligand interactions.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Kennedy, Professor Malcolm and Cooper, Professor Alan
Authors: Kennedy, M.W., Heikema, A.P., Cooper, A., Bjorkman, P.J., and Sanchez, L.M.
Subjects:Q Science > QD Chemistry
Q Science > QH Natural history > QH345 Biochemistry
College/School:College of Science and Engineering > School of Chemistry
Journal Name:Journal of Biological Chemistry
Journal Abbr.:J Biol Chem.
Publisher:American Society for Biochemistry and Molecular Biology, Inc.
ISSN:0021-9258
ISSN (Online):1083-351X
Published Online:25 June 2001

University Staff: Request a correction | Enlighten Editors: Update this record