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The protein C ω‐loop substitution Asn2Ile is associated with reduced protein C anticoagulant activity
Author(s) -
Preston Roger J. S.,
Morse Colin,
Murden Sherina L.,
Brady Sara Kate,
O’Donnell James S.,
Mumford Andrew D.
Publication year - 2009
Publication title -
british journal of haematology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.907
H-Index - 186
eISSN - 1365-2141
pISSN - 0007-1048
DOI - 10.1111/j.1365-2141.2008.07550.x
Subject(s) - protein c , thrombomodulin , recombinant dna , endothelial protein c receptor , microbiology and biotechnology , protein s , anticoagulant , thrombin , chemistry , biology , biochemistry , medicine , immunology , platelet , gene
Summary 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 ω‐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.