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.
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subunit gene showed that case no. 1 had a deletion of 4 bp (AATT) in exon XI and that, in case no. 2, Gly562 (GGG) had been replaced by Arg(AGG).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.
Takahashi
N
N
Department of Molecular Patho-Biochemistry, Yamagata University School of Medicine, Yamagata, Japan.
Tsukamoto
H
H
Umeyama
H
H
Castaman
G
G
Rodeghiero
F
F
Ichinose
A
A
D001120:Arginine / Q000235:genetics; D005176:Factor XIII / Q000737:chemistry / Q000235:genetics*; D005177:Factor XIII Deficiency / Q000235:genetics*; D005998:Glycine / Q000235:genetics; D006801:Humans; D017354:Point Mutation; D011487:Protein Conformation; D011995:Recombination, Genetic; D017384:Sequence Deletion; D013329:Structure-Activity Relationship
D005176:Factor XIII; D001120:Arginine; D005998:Glycine