Zinc-induced oligomerization of zinc α2 glycoprotein reveals multiple fatty acid-binding sites.
Zinc α2 glycoprotein (ZAG) is an adipokine with a class I MHC protein fold and is associated with obesity and diabetes. Although its intrinsic ligand remains unknown, ZAG binds the dansylated C11 fatty acid 11-(dansylamino)undecanoic acid (DAUDA) in the groove between the α1 and α2 domains. The surface of ZAG has approximately 15 weak zinc-binding sites deemed responsible for precipitation from human plasma. In the present study the functional significance of these metal sites was investigated. Analytical ultracentrifugation (AUC) and CD showed that zinc, but not other divalent metals, causes ZAG to oligomerize in solution. Thus ZAG dimers and trimers were observed in the presence of 1 and 2 mM zinc. Molecular modelling of X-ray scattering curves and sedimentation coefficients indicated a progressive stacking of ZAG monomers, suggesting that the ZAG groove may be occluded in these. Using fluorescence-detected sedimentation velocity, these ZAG-zinc oligomers were again observed in the presence of the fluorescent boron dipyrromethene fatty acid C16-BODIPY (4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3-hexadecanoic acid). Fluorescence spectroscopy confirmed that ZAG binds C16-BODIPY. ZAG binding to C16-BODIPY, but not to DAUDA, was reduced by increased zinc concentrations. We conclude that the lipid-binding groove in ZAG contains at least two distinct fatty acid-binding sites for DAUDA and C16-BODIPY, similar to the multiple lipid binding seen in the structurally related immune protein CD1c. In addition, because high concentrations of zinc occur in the pancreas, the perturbation of these multiple lipid-binding sites by zinc may be significant in Type 2 diabetes where dysregulation of ZAG and zinc homoeostasis occurs.
Diabetes and Nutritional Sciences Division, Franklin Wilkins Building, 150 Stamford Street, King's College London, London SE1 9NH, U.K. Department of Structural and Molecular Biology, University College London, Darwin Building, Gower Street, London WC1E 6BT, U.K.
Henna
H
Zahid
Diabetes and Nutritional Sciences Division, Franklin Wilkins Building, 150 Stamford Street, King's College London, London SE1 9NH, U.K.
Layeque
L
Miah
Diabetes and Nutritional Sciences Division, Franklin Wilkins Building, 150 Stamford Street, King's College London, London SE1 9NH, U.K. Department of Structural and Molecular Biology, University College London, Darwin Building, Gower Street, London WC1E 6BT, U.K.
Andy M
AM
Lau
Department of Structural and Molecular Biology, University College London, Darwin Building, Gower Street, London WC1E 6BT, U.K.
Lea
L
Brochard
Diabetes and Nutritional Sciences Division, Franklin Wilkins Building, 150 Stamford Street, King's College London, London SE1 9NH, U.K.
Debolina
D
Hati
Biomolecular Spectroscopy Centre, Optical and Chiroptical Spectroscopy Facility, The Wolfson Wing, Hodgkin Building, King's College London, London SE1 1UL, U.K.
Tam T T
TT
Bui
Biomolecular Spectroscopy Centre, Optical and Chiroptical Spectroscopy Facility, The Wolfson Wing, Hodgkin Building, King's College London, London SE1 1UL, U.K.
Alex F
AF
Drake
Department of Structural and Molecular Biology, University College London, Darwin Building, Gower Street, London WC1E 6BT, U.K.
Jayesh
J
Gor
Department of Structural and Molecular Biology, University College London, Darwin Building, Gower Street, London WC1E 6BT, U.K.
Stephen J
SJ
Perkins
Diabetes and Nutritional Sciences Division, Franklin Wilkins Building, 150 Stamford Street, King's College London, London SE1 9NH, U.K. Department of Structural and Molecular Biology, University College London, Darwin Building, Gower Street, London WC1E 6BT, U.K. l.mcdermott@ucl.ac.uk.
Lindsay C
LC
McDermott
D054392:Adipokines; D001665:Binding Sites / Q000502:physiology; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D005227:Fatty Acids / Q000737:chemistry / Q000378:metabolism*; D006023:Glycoproteins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D015032:Zinc / Q000378:metabolism* / Q000494:pharmacology; D000090203:Zn-Alpha-2-Glycoprotein
D054392:Adipokines; D002352:Carrier Proteins; D005227:Fatty Acids; D006023:Glycoproteins; D015032:Zinc; C488891:AZGP1 protein, human; D000090203:Zn-Alpha-2-Glycoprotein
analytical ultracentrifugation; fatty acids; fluorescence; obesity; oligomerization; zinc α2 glycoprotein