The protein C omega-loop substitution Asn2Ile is associated with reduced protein C anticoagulant activity

Br J Haematol. 2009 Mar;144(6):946-53. doi: 10.1111/j.1365-2141.2008.07550.x. Epub 2008 Dec 26.


We report a kindred with heritable protein C (PC) deficiency in which two siblings with severe thrombosis showed a composite type I and IIb PC deficiency phenotype, identified using commercial PC assays (proband: PC antigen 42 u/dl, amidolytic activity 40 u/dl, anticoagulant activity 9 u/dl). The independent PROC nucleotide variations c.669C>A (predictive of Ser181Arg) and c.131C>T (predictive of Asn2Ile) segregated with the type I and type IIb PC deficiency phenotypes respectively, but co-segregated in the siblings with severe thrombosis. Soluble thrombomodulin (sTM)-mediated inhibition of plasma thrombin generation from an individual with PC-Asn2Ile was lower (endogenous thrombin potential (ETP) 56 +/- 1% that of ETP determined without sTM) than control plasma (ETP 15 +/- 2%) indicating reduced PC anticoagulant activity. Recombinant APC-Asn2Ile exhibited normal amidolytic activity but impaired anticoagulant activity. Protein S (PS)-dependent anticoagulant activity of recombinant APC-Asn2Ile and binding of recombinant APC-Asn2Ile to endothelial protein C receptor (EPCR) were reduced compared to recombinant wild-type APC. Asn2 lies within the omega-loop of the PC/APC Gla domain and this region is critical for calcium-induced folding and subsequent interactions with anionic phospholipids, EPCR and PS. The disruption of these interactions in this naturally-occurring PC variant highlights their collective importance in mediating APC anticoagulant activity in vivo.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Aged
  • Amino Acid Substitution*
  • Autoantigens / blood
  • Blood Coagulation / genetics*
  • Blood Coagulation Tests
  • Child
  • Female
  • Genotype
  • Humans
  • Male
  • Pedigree
  • Phenotype
  • Protein C / genetics*
  • Protein C / immunology
  • Protein C / metabolism
  • Protein C Deficiency / complications
  • Protein C Deficiency / genetics*
  • Protein C Deficiency / metabolism
  • Purpura Fulminans / genetics
  • Thrombin / biosynthesis
  • Thrombosis / etiology
  • Thrombosis / genetics


  • Autoantigens
  • Protein C
  • Thrombin