Protein C Thr315Ala variant results in gain of function but manifests as type II deficiency in diagnostic assays.
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Ding Q, Yang L, Dinarvand P, Wang X, Rezaie AR
Protein C Thr315Ala variant results in gain of function but manifests as type II deficiency in diagnostic assays.
Blood. 2015 Apr 9;125(15):2428-34. doi: 10.1182/blood-2014-12-617274. Epub 2015 Feb 4.
- PubMed ID
- 25651845 [ View in PubMed]
- Abstract
Protein C (PC) is a vitamin K-dependent plasma glycoprotein, which upon activation by thrombin in complex with thrombomodulin (TM), regulates the coagulation cascade through a feedback loop inhibition mechanism. PC deficiency is associated with an increased risk of venous thromboembolism (VTE). A recent cohort study aimed at establishing a normal PC range identified a healthy PC-deficient subject whose PC antigen level of 65% and activity levels of 50% (chromogenic assay) and 36% (clotting assay) were markedly low. The proband has a negative family history of VTE. Genetic analysis revealed the proband has a heterozygous missense mutation in which Thr-315 of the PC heavy chain has been substituted with Ala. We expressed this mutant in HEK-293 cells and purified it to homogeneity. A similar decrease in both anticoagulant and anti-inflammatory activities of the activated protein C mutant was observed in plasma- and cell-based assays. Interestingly, we discovered if functional assays were coupled to PC activation by the thrombin-TM complex, the variant exhibits improved activities in all assays. Sequence analysis revealed Thr-315 is a consensus N-linked glycosylation site for Asn-313 and that its elimination significantly ( approximately four- to fivefold) improves the maximum velocity of PC activation by the thrombin-TM complex, explaining the basis for the proband's negative VTE pedigree.