Thromb Haemost 2001; 86(04): 1023-1027
DOI: 10.1055/s-0037-1616528
Special Article
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Creation of an Additional Glycosylation Site as a Mechanism for Type I Antithrombin Deficiency

Alison C. Fitches
1   Department of Pathology, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand
,
Krzysztof Lewandowski
2   Department of Haematology, Karol Marcinkowski University of Medical Sciences, Poznan, Poland
,
Robin J. Olds
1   Department of Pathology, Dunedin School of Medicine, University of Otago, Dunedin, New Zealand
› Author Affiliations
Further Information

Publication History

Received 18 December 2000

Accepted after resubmission 16 May 2001

Publication Date:
09 December 2017 (online)

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Summary

We report the identification of a new mutation resulting in type I antithrombin (AT) deficiency and the mechanism by which the deficiency arose. The single base substitution of G to A at nucleotide 2709 was identified in a proband with a family history of venous thrombosis. The mutation results in a substitution of 82 Ser by Asn, creating a new glycosylation site. Expression studies were then carried out, to confirm Asn-linked glycosylation occurred at this consensus site and that this resulted in the AT deficient phenotype. Cell-free translations using rabbit reticulocyte lysate in the presence of microsomes demonstrated that the 82 Asn variant was post-translationally processed efficiently. The 82 Asn variant protein was of a higher molecular weight than normal AT, consistent with the addition of a fifth glycan chain. Incubation of translation product with endoglycosidase H, confirmed that the higher molecular weight product had resulted from additional carbohydrate. Expression of the 82 Asn variant in COS-7 cells resulted in intracellular accumulation, with a low level of secretion of the protein into culture supernatant, consistent with type I AT deficiency. The addition of an extra carbohydrate side chain to residue 82 of antithrombin may block post-translational folding, trapping the variant intracellulary.

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