Distinct C-terminus of the B subunit of factor XIII in a population-associated major phenotype: the first case of complete allele-specific alternative splicing products in the coagulation and fibrinolytic systems.
OBJECTIVE
The purpose of this study was to elucidate the molecular bases of the heterogeneity of the B subunit of coagulation factor XIII (FXIII-B), classified by isoelectric focusing into its three population-associated major phenotypes.


RESULTS
By genetic sequencing and polymerase chain reaction (PCR)-restriction fragment length polymorphism analyses, a C-to-G change was identified in intron K for the Asian-associated major phenotype FXIII-B*3. A transcript containing the novel exon XII' was detected by reverse transcription PCR using hepatocyte cell lines with this allele. The exclusive existence of a novel C-terminal peptide in a homozygote of FXIII-B*3 was also detected by matrix-assisted laser-desorption ionization time of flight mass spectrometry. The FXIII-B*3 isoform had a C-terminus 15 residues longer than the other isoforms, containing two additional basic amino acids and one extra acidic amino acid. Accordingly, the C-to-G nucleotide substitution created an efficient splice acceptor AG dinucleotide, which resulted in allele-specific alternative splicing in intron K. When compared with FXIII-B*1, the third major phenotype, FXIII-B*2, had an A-to-G change in exon III, converting His95 to Arg, and a rare phenotype, FXIII-B*4, had an A-to-T change in exon VII, converting Glu368 to Val.


CONCLUSIONS
We found an extremely rare event of complete allele-specific alternative splicing for FXIII-B. The FXIII-B*3 isoform had a distinct C-terminal peptide, while the FXIII-B*2 and FXIII-B*4 isoforms had His95 to Arg and Glu368 to Val substitutions, respectively, which led to differential isoelectric points of these isoforms. Such variations in the amino acid sequence of FXIII-B may have profound effects on its structure-function relationship, plasma FXIII levels, and disease susceptibility.
Department of Molecular Patho-Biochemistry, Yamagata University School of Medicine, Yamagata, Japan.
H
H
Iwata
T
T
Kitano
K
K
Umetsu
I
I
Yuasa
K
K
Yamazaki
B
B
Kemkes-Matthes
A
A
Ichinose
D000483:Alleles; D017398:Alternative Splicing; D000595:Amino Acid Sequence; D001483:Base Sequence; D001777:Blood Coagulation; D005176:Factor XIII / Q000737:chemistry / Q000235:genetics*; D005342:Fibrinolysis; D005828:Genetics, Population; D006801:Humans; D008969:Molecular Sequence Data; D010641:Phenotype; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D012333:RNA, Messenger / Q000235:genetics; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D012333:RNA, Messenger; D005176:Factor XIII; C054380:factor XIIIb