title: Comparative analyses of pentraxins: implications for protomer assembly and ligand binding.
abstract: BACKGROUND
  Pentraxins are a family of plasma proteins characterized by their pentameric assembly and calcium-dependent ligand binding. The recent determination of the crystal structure for a member of this family, human serum amyloid P component (SAP), provides a basis for the comparative analysis of the pentraxin family.
  
  
  RESULTS
  We have compared the sequences, tertiary structures and quaternary arrangements of SAP with human C-reactive protein (CRP), Syrian hamster SAP (HSAP) and Limulus polyphemus CRP (LIM). These proteins can adopt a beta-jelly roll topology and a hydrophobic core similar to that seen in SAP. Only minor differences are observed in the positions of residues involved in coordinating calcium ions.
  
  
  CONCLUSIONS
  Calcium-mediated ligand binding by CRP, HSAP and LIM is similar to that defined by the crystal structure of SAP, but sequence differences in the hydrophobic pocket explain the differential ligand specificities exhibited by the homologous proteins. Differences elsewhere, including insertions and deletions, account for the different (hexameric) quaternary structure of LIM.
authors.affiliation: Laboratory of Molecular Biology, Birkbeck College, University of London, UK.
authors.forename: N
authors.initials: N
authors.lastname: Srinivasan
authors.forename: H E
authors.initials: HE
authors.lastname: White
authors.forename: J
authors.initials: J
authors.lastname: Emsley
authors.forename: S P
authors.initials: SP
authors.lastname: Wood
authors.forename: M B
authors.initials: MB
authors.lastname: Pepys
authors.forename: T L
authors.initials: TL
authors.lastname: Blundell
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D005075:Biological Evolution; D001798:Blood Proteins / Q000737:chemistry* / Q000235:genetics; D002097:C-Reactive Protein / Q000737:chemistry / Q000235:genetics; D002118:Calcium / Q000737:chemistry; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000235:genetics; D006224:Cricetinae; D006737:Horseshoe Crabs; D006801:Humans; D008024:Ligands; D008647:Mesocricetus; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D000683:Serum Amyloid P-Component / Q000737:chemistry / Q000235:genetics
chemical_list: D001798:Blood Proteins; D002135:Calcium-Binding Proteins; D008024:Ligands; D000683:Serum Amyloid P-Component; D002097:C-Reactive Protein; D002118:Calcium