Antithrombin-III-Hamilton: a gene with a point mutation (guanine to
adenine) in codon 382 causing impaired serine protease reactivity
R Devraj-Kizuk, DH Chui, EV Prochownik, CJ Carter, FA Ofosu and MA Blajchman
Canadian Red Cross Blood Transfusion Service, Department of Pathology,
McMaster University, Hamilton, Ontario.
Antithrombin-III-Hamilton is a structural mutant of antithrombin III with
defective serine protease reactivity, demonstrable in three members of a
French Canadian family. The propositus, a 54-year-old man with a history of
recurrent thromboembolic events, and his two asymptomatic grown children
are heterozygous for the mutant antithrombin III gene. In all three
individuals, the immunoreactive antithrombin III level is normal, while the
antithrombin and antifactor Xa activity is approximately 50% of the control
value. Two dimensional immunoelectrophoresis of antithrombin-III-Hamilton
in the presence of heparin is normal. Purified antithrombin-III-Hamilton
did not form thrombin-antithrombin III complex when incubated with thrombin
for up to 30 minutes. The normal and mutant antithrombin III alleles of the
propositus could be distinguished by linkage to Pstl restriction fragment
length polymorphisms (RFLP). Genomic DNA from the propositus was cloned
into EMBL 3 phage vectors and two clones containing nearly complete copies
of the antithrombin-III-Hamilton allele were identified. Exon 6 of both
clones was subcloned into M13 phage vector and sequenced, revealing a
G----A point mutation in the first base of codon 382. Codon 382 codes for
alanine in the normal allele and for threonine in the
antithrombin-III-Hamilton allele. Alanine-382, 12 residues from the
reactive center, is a highly conserved amino acid in the family of serine
protease inhibitors known as the serpins. We postulate that, as a result of
the substitution of threonine for alanine in antithrombin-III-Hamilton,
either the tertiary structure or the hydrophobicity of the thrombin-binding
region is altered, causing aberrant conformation of the Arg-393-Ser-394
bond at the reactive center impairing the interaction between
antithrombin-III-Hamilton and the activated serine proteases.
Volume 72,
Issue 5,
pp. 1518-1523,
11/01/1988
Copyright © 1988 by The American Society of Hematology
