Identification and characterization of a novel variant in C-terminal region of Antithrombin (Ala427Thr) associated with
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Identification and characterization of a novel variant in C‑terminal region of Antithrombin (Ala427Thr) associated with type II AT deficiency leading to polymer formation Teena Bhakuni1 · Amit Sharma2 · Arijit Biswas3 · Shadabi Bano1 · Manoranjan Mahapatra2 · Renu Saxena2 · Mohamad Aman Jairajpuri1
© Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Antithrombin (AT) deficiency is a rare but strong risk factor for the thrombosis development. Mutations in gene encoding AT (SERPINC1) have provided a detailed understanding of AT deficiency and subsequent development of thrombotic complications. In the present study, we describe a case of thrombotic patient with reduced AT activity and normal AT antigen levels. AT deficiency in the patient was explained by the presence of heterozygous mutation g.13397A>G (Ala427Thr) in exon 6 of SERPINC1. Reduced APTT and TT with normal PT were observed. The mutation was found to be absent in healthy controls (n = 62). In vitro purification and characterization of variant AT showed significant decrease in fluorescence emission intensity, decreased bis-ANS fluorescence emission, changes in secondary structure and presence of polymerized AT in patient’s plasma as assessed by fluorescence, circular dichroism and transmission electron microscopy respectively. Furthermore, molecular dynamics simulation studies showed altered conformation due to Ala427Thr substitution. Our study shows that genetic screening should be carried out in AT deficient patients in addition to the routinely used functional assays to understand the molecular basis of disease development. Keywords Antithrombin · Molecular dynamics simulation · Mutations · Polymerization · Thrombosis
Highlights • We identified a novel heterozygous mutation in SER-
PINC1 gene, Ala427Thr; in an Indian patient with type II AT deficiency. • Purified Ala427Thr AT protein showed polymeric nature and altered secondary and tertiary structures as compared to the wild type AT.
* Mohamad Aman Jairajpuri [email protected] 1
Protein Conformation and Enzymology Lab, Department of Biosciences, Jamia Millia Islamia, Jamia Nagar, New Delhi, 110025, India
2
Department of Hematology, All India Institute of Medical Sciences, New Delhi, 110029, India
3
Institute of Experimental Haematology and Transfusion Medicine, University Clinic Bonn, Bonn, Germany
• Our study shows that in addition to functional assays,
genetic analyses should be carried out in AT deficient patients.
Introduction Antithrombin (AT) deficiency is a rare, autosomal dominant defect associated with increased risk of deep vein thrombosis (DVT). With the advent of twentieth century, thrombosis has become a major contributor towards global disease burden caused by non-communicable diseases [1]. Owing to the genetic differences in Indian and Western population, DVT has been perceived to be far less common in Indians, however; recent studies show similar prevalence in both the population [2–4]. Along with acquired causes of AT deficiency that
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