Molecular Mechanisms of Type II Factor XIII Deficiency: Novel
Gly562-Arg Mutation and C-Terminal Truncation of the A
Subunit Cause Factor XIII Deficiency as Characterized in a Mammalian
Expression System
Nobumasa Takahashi,
Hiroaki Tsukamoto,
Hideaki Umeyama,
Giancarlo Castaman,
Francesco Rodeghiero, and
Akitada Ichinose
From the Department of Molecular Patho-Biochemistry, Yamagata
University School of Medicine, Yamagata, Japan; the Department of
Physical Chemistry, Kitasato University School of Pharmaceutical
Sciences, Tokyo, Japan; the Department of Haematology, San Bortolo
Hospital, Vicenza, Italy.
To explore the biological and clinical implications of the
structure/function relationships in factor XIII, mutations in two patients with type II deficiency were identified and characterized in a
mammalian expression system. Nucleotide sequence analysis of the A
subunit gene showed that case no. 1 had a deletion of 4 bp (AATT) in
exon XI and that, in case no. 2, Gly562 (GGG) had been replaced by
Arg(AGG). The deletion in case no. 1 leads to a premature
termination at codon 464. Restriction digestion of amplified DNAs
confirmed that both cases were homozygous for their respective
mutations. Reverse transcription-polymerase chain reaction analysis demonstrated that the level of mRNA was greatly reduced in
case no. 1, whereas the level of mutant mRNA expressed in case no. 2 was normal. Molecular modeling calculated that Arg562 changed the
conformation of the A subunit, suggesting misfolding and/or destabilization of the molecule. To determine how these mutations impaired synthesis of the A subunit, recombinant A subunits bearing the
mutations were expressed in mammalian cells. Pulse-chase experiments showed that the mutants were synthesized normally but disappeared rapidly, whereas the wild-type remained. These results indicate that
both mutant proteins with an altered conformation become prone to rapid
degradation, resulting in factor XIII deficiency in these patients.
Blood, Vol. 91 No. 8 (April 15), 1998:
pp. 2830-2838
© 1998 by The American Society of Hematology.
