A C-terminal amino acid substitution in the gamma-chain caused by a novel heterozygous frameshift mutation (Fibrinogen Matsumoto VII) results in hypofibrinogenaemia

作者：Fujihara Noriko; Haneishi Ayumi; Yamauchi Kazuyoshi; Terasawa Fumiko; Ito Toshiro; Ishida Fumihiro; Okumura Nobuo^*

来源：Thrombosis and Haemostasis, 2010, 104(2): 213-223.

DOI：10.1160/TH09-08-0540

• Hypofibrinogenaemia
• nucleotide deletion
• frameshift mutation
• assembly
• secretion

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 gamma Delta 7651A and gamma Delta 7651A/399T (gamma Delta 7651A 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.

• 出版日期2010-8