The structures of crystalline complexes of human serum amyloid P component with its carbohydrate ligand, the cyclic pyruvate acetal of galactose.
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.
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School of Biological Science, University of Southampton, Bassett Crescent East, Hampshire, UK. darren@soton.ac.uk
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D002118:Calcium / Q000737:chemistry; D002241:Carbohydrates / Q000737:chemistry; D018360:Crystallography, X-Ray; D005690:Galactose / Q000031:analogs & derivatives* / Q000737:chemistry*; D006801:Humans; D008024:Ligands; D008958:Models, Molecular; D017434:Protein Structure, Tertiary; D000683:Serum Amyloid P-Component / Q000737:chemistry*
D002241:Carbohydrates; D008024:Ligands; D000683:Serum Amyloid P-Component; C034485:4,6-pyruvylated galactose; D002118:Calcium; D005690:Galactose