The structures of crystalline complexes of human serum amyloid P component with its carbohydrate ligand, the cyclic pyruvate acetal of galactose

J Mol Biol. 2002 Jul 26;320(5):1081-6. doi: 10.1016/s0022-2836(02)00514-4.

Abstract

Two monoclinic (P2(1)) crystal forms of human serum amyloid P component (SAP) in complex with the 4,6-pyruvate acetal of beta-D-galactose (MObetaDG) were prepared. Structure analysis by molecular replacement and refinement at 2.2A resolution revealed that crystal form 1 (a=95.76A, b=70.53A, c=103.41A, beta=96.80 degrees) contained a pentamer in the asymmetric unit with a structure very similar to that of the published search model. The mode of ligand co-ordination was also similar except that four of the five subunits showed bound ligand with an additional H-bond between O1 of the galactose and the side-chain of Lys79. One sub-unit showed no bound ligand and a vacant calcium site close to a crystal contact. The 2.6A resolution structure of crystal form 2 (a=118.60A, b=109.10A, c=120.80A and beta=95.16 degrees ) showed ten sub-units in the asymmetric unit, all with two bound calcium ions and ligand. The most extensive protein-protein interactions between pentamers describe an AB face-to-face interaction involving 15 ion pairs that sandwiches five molecules of bound MObetaDG at the interface.

MeSH terms

  • Calcium / chemistry
  • Carbohydrates / chemistry
  • Crystallography, X-Ray
  • Galactose / analogs & derivatives*
  • Galactose / chemistry*
  • Humans
  • Ligands
  • Models, Molecular
  • Protein Structure, Tertiary
  • Serum Amyloid P-Component / chemistry*

Substances

  • Carbohydrates
  • Ligands
  • Serum Amyloid P-Component
  • 4,6-pyruvylated galactose
  • Calcium
  • Galactose

Associated data

  • PDB/1GYK
  • PDB/R1GYKSF