Crystallographic studies of ligand binding by Zn-alpha2-glycoprotein.
Zn-alpha2-glycoprotein (ZAG) is a 41 kDa soluble protein that is present in most bodily fluids. The previously reported 2.8 A crystal structure of ZAG isolated from human serum demonstrated the structural similarity between ZAG and class I major histocompatibility complex (MHC) molecules and revealed a non-peptidic ligand in the ZAG counterpart of the MHC peptide-binding groove. Here we present crystallographic studies to explore further the nature of the non-peptidic ligand in the ZAG groove. Comparison of the structures of several forms of recombinant ZAG, including a 1.95 A structure derived from ZAG expressed in insect cells, suggests that the non-peptidic ligand in the current structures and in the structure of serum ZAG is a polyethylene glycol (PEG), which is present in the crystallization conditions used. Further support for PEG binding in the ZAG groove is provided by the finding that PEG displaces a fluorophore-tagged fatty acid from the ZAG binding site. From these results we hypothesize that our purified forms of ZAG do not contain a bound endogenous ligand, but that the ZAG groove is capable of binding hydrophobic molecules, which may relate to its function.
Division of Biology, 114-96 Pasadena, CA 91125, USA.
Silvia L
SL
Delker
Anthony P
AP
West
Lindsay
L
McDermott
Malcolm W
MW
Kennedy
Pamela J
PJ
Bjorkman
D054392:Adipokines; D001665:Binding Sites; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics*; D018360:Crystallography, X-Ray / Q000379:methods; D003619:Dansyl Compounds / Q000737:chemistry; D005227:Fatty Acids / Q000737:chemistry; D005456:Fluorescent Dyes / Q000737:chemistry; D006023:Glycoproteins / Q000737:chemistry* / Q000235:genetics*; D006031:Glycosylation; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D010455:Peptides / Q000737:chemistry; D011092:Polyethylene Glycols / Q000737:chemistry; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry; D015032:Zinc / Q000737:chemistry*; D000090203:Zn-Alpha-2-Glycoprotein
D054392:Adipokines; D002352:Carrier Proteins; D003619:Dansyl Compounds; D005227:Fatty Acids; D005456:Fluorescent Dyes; D006023:Glycoproteins; D008024:Ligands; D010455:Peptides; D011092:Polyethylene Glycols; D011994:Recombinant Proteins; D015032:Zinc; C488891:AZGP1 protein, human; D000090203:Zn-Alpha-2-Glycoprotein; C054400:11-(dansylamino)undecanoic acid