Identification and characterization of a novel variant in C-terminal region of Antithrombin (Ala427Thr) associated with type II AT deficiency leading to polymer formation

Naringin binds to protein disulfide isomerase to inhibit its activity and modulate the blood coagulation rates: Implications in controlling thrombosis

Currently used antithrombotic drugs are beset with several drawbacks which necessitates the need for new and cheaper alternatives. Protein disulfide isomerase (PDI) is secreted in the blood plasma in cellular stress conditions and initiates the thrombus formation. A screening of library of natural compounds revealed that naringin had a high binding affinity for the PDI (-8.2 kcal/mol). Recombinant PDI was purified using the affinity chromatography. Incubation of purified PDI (3 μM) with naringin (0-100 μM, pH 7.4, 25 °C) partially modulated its conformation. Consequently, the fluorescence emission spectra of the PDI binding to naringin were assessed using the Stern-Volmer equation, which indicated an association constant of 2.78 × 104 M-1 suggesting an appreciable affinity for the naringin, with a unique binding site. An insulin turbidity assay showed that PDI activity is decreased in the presence of naringin indicating inhibition. Molecular dynamic simulation studies showed the changes in the PDI structure on binding to the naringin. Incubation of naringin (80 μM) in fresh human plasma along with exogenous PDI (175 nM) showed a significant delay in the intrinsic and extrinsic coagulation pathways. We show that naringin is able to modulate the PDI conformation and activity resulting in altered blood coagulation rates.

Mannose 2, 3, 4, 5, 6-O-pentasulfate (MPS): a partial activator of human heparin cofactor II with anticoagulation potential

Thromboembolic diseases are a major cause of mortality in human and the currently available anticoagulants are associated with various drawbacks, therefore the search for anticoagulants that have better safety profile is highly desirable. Compounds that are part of the dietary routine can be modified to possibly increase their anticoagulant potential. We show mannose 2,3,4,5,6-O-pentasulfate (MPS) as a synthetically modified form of mannose that has appreciable anticoagulation properties. An in silico study identified that mannose in sulfated form can bind effectively to the heparin-binding site of antithrombin (ATIII) and heparin cofactor II (HCII). Mannose was sulfated using a simple sulfation strategy-involving triethylamine-sulfur trioxide adduct. HCII and ATIII were purified from human plasma and the binding analysis using fluorometer and isothermal calorimetry showed that MPS binds at a unique site. A thrombin inhibition analysis using the chromogenic substrate showed that MPS partially enhances the activity of HCII. Further an assessment of in vitro blood coagulation assays using human plasma showed that the activated partial thromboplastin time (APTT) and prothrombin time (PT) were prolonged in the presence of MPS. A molecular dynamics simulation analysis of the HCII-MPS complex showed fluctuations in a N-terminal loop and the cofactor binding site of HCII. The results indicate that MPS is a promising lead due to its effect on the in vitro coagulation rate.Communicated by Ramaswamy H. Sarma.

Novel SERPINC1 missense mutation (Cys462Tyr) causes disruption of the 279Cys-462Cys disulfide bond and leads to type Ⅰ hereditary antithrombin deficiency

BACKGROUND

Antithrombin (AT) is the primary physiological anticoagulant of normal hemostasis. Hereditary AT deficiency, an autosomal dominant thrombotic disease caused by mutations in the AT gene (SERPINC1), is associated with venous thromboembolism.

OBJECTIVE

We investigated the phenotypes, genotypes, and pathogenesis of hereditary AT deficiency in a 12-year-old boy (proband) who developed a pulmonary embolism and a subsequent deep vein thrombosis.

METHODS

The AT activity and AT antigen level of the proband and his family members were measured. Mutation sites in all seven exons of SERPINC1 were identified. Analysis of conserved regions around codon 462 of the SERPINC1 gene and functional predictions were performed using bioinformatics tools.

RESULTS

The proband, his father, and his paternal grandmother demonstrated reduced AT activity and antigen levels consistent with Type I AT deficiency. A novel heterozygous missense mutation, c.1385G>A (Cys462Tyr) was identified in all three symptomatic family members. This missense mutation causes disruption of the 279Cys-462Cys disulfide bond and leads to type Ⅰ hereditary AT deficiency.

CONCLUSION

A SERPINC1 missense mutation (Cys462Tyr) causing damage to the 279Cys-462Cys disulfide bond of the AT protein appears to be the cause of Type I AT deficiency in this family. These findings indicate one pathological mechanism associated with hereditary AT deficiency.