Crystallographic studies of ligand binding by Zn-alpha2-glycoprotein

J Struct Biol. 2004 Nov;148(2):205-13. doi: 10.1016/j.jsb.2004.04.009.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adipokines
  • Binding Sites
  • Carrier Proteins / chemistry*
  • Carrier Proteins / genetics*
  • Crystallography, X-Ray / methods
  • Dansyl Compounds / chemistry
  • Fatty Acids / chemistry
  • Fluorescent Dyes / chemistry
  • Glycoproteins / chemistry*
  • Glycoproteins / genetics*
  • Glycosylation
  • Humans
  • Ligands
  • Models, Molecular
  • Peptides / chemistry
  • Polyethylene Glycols / chemistry
  • Protein Structure, Secondary
  • Recombinant Proteins / chemistry
  • Zinc / chemistry*


  • AZGP1 protein, human
  • Adipokines
  • Carrier Proteins
  • Dansyl Compounds
  • Fatty Acids
  • Fluorescent Dyes
  • Glycoproteins
  • Ligands
  • Peptides
  • Recombinant Proteins
  • Polyethylene Glycols
  • 11-(dansylamino)undecanoic acid
  • Zinc