A C-terminal amino acid substitution in the gamma-chain caused by a novel heterozygous frameshift mutation (Fibrinogen Matsumoto VII) results in hypofibrinogenaemia.
We found a novel hypofibrinogenemia designated as Matsumoto VII (M-VII), which is caused by a heterozygous nucleotide deletion at position g.7651 in FGG and a subsequent frameshift mutation in codon 387 of the gamma-chain. This frameshift results in 25 amino acid substitutions, late termination of translation with elongation by 15 amino acids, and the introduction of a canonical glycosylation site. Western blot analysis of the patient's plasma fibrinogen visualised with anti-gamma-chain antibody revealed the presence of two extra bands. To identify the extra bands and determine which of the above-mentioned alterations caused the assembly and/or secretion defects in the patient, 11 variant vectors that introduced mutations into the cDNA of the gamma-chain or gamma'-chain were transfected into Chinese hamster ovary cells. In vitro expression of transfectants containing gammaDelta7651A and gammaDelta7651A/399T (gammaDelta7651A with an amino acid substitution of 399Asn by Thr and a variant lacking the canonical glycosylation site) demonstrated a reduction in secretion to approximately 20% of the level seen in the transfectants carrying the normal gamma-chain. Furthermore, results from other transfectants demonstrated that eight aberrant residues between 391 and 398 of the M-VII variant, rather than the 15 amino acid extension or the additional glycosylation, are responsible for the reduced levels of assembly and secretion of M-VII variant fibrinogen. Finally, the results of this study and our previous reports demonstrate that the fibrinogen gamma-chain C-terminal tail (388-411) is not necessary for protein assembly or secretion, but the aberrant amino acid sequence observed in the M-VII variant (especially 391-398) disturbs these functions.
Fujihara
Noriko
N
Department of Laboratory Medicine, Shinshu University Hospital, Matsumoto, Japan. nobuoku@shinshu-u.ac.jp
Haneishi
Ayumi
A
Yamauchi
Kazuyoshi
K
Terasawa
Fumiko
F
Ito
Toshiro
T
Ishida
Fumihiro
F
Okumura
Nobuo
N
D000347:Afibrinogenemia / Q000097:blood / Q000235:genetics*; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D001777:Blood Coagulation / Q000235:genetics*; D001780:Blood Coagulation Tests; D015153:Blotting, Western; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D004252:DNA Mutational Analysis; D005260:Female; D015241:Fibrinogens, Abnormal / Q000235:genetics* / Q000378:metabolism; D016368:Frameshift Mutation; D020022:Genetic Predisposition to Disease; D006031:Glycosylation; D006579:Heterozygote; D006801:Humans; D007564:Japan; D008875:Middle Aged; D008969:Molecular Sequence Data; D010641:Phenotype; D055503:Protein Multimerization; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D014162:Transfection
D015241:Fibrinogens, Abnormal; C553826:fibrinogen Matsumoto VII