血友病B由因子IX蛋白酶结构域的五种不同的非缺失突变引起。
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Ludwig M, Sabharwal AK, Brackmann HH, Olek K, Smith KJ, Birktoft JJ, Bajaj SP
血友病B由因子IX蛋白酶结构域的五种不同的非缺失突变引起。
《血液》1992年3月1日;79(5):1225-32。
- PubMed ID
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1346975 (PubMed视图］
- 摘要
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因子IX是一种多结构域蛋白，是丝氨酸蛋白酶(因子IXa)的原酶，对止血至关重要。在本报告中，我们描述了5例IX因子基因既没有缺失也没有重排的血友病B(缺乏IX因子活性)的分子基础。通过所有外显子和启动子区域的酶扩增和测序，在每位患者中鉴定出因子IX蛋白酶域的以下致病突变:IXSchmallenberg:核苷酸31,215G----T, Ser365Ile;IXVarel:核苷酸31,214A----G, Ser365Gly;IXMechtal: nucleotide 31,211G----C, Asp364His;IXDreihacken:核苷酸30,864G----A, Arg248Gln;IXMonschau:核苷酸30,855A----T, Glu245Val。在IXVarel中，核苷酸31213t也被C取代，导致Asp-364位点发生沉默突变(GAT----GAC)。因此，该患者在核苷酸31213和31214处发生了TA到CG的双碱基对替换，但只有Ser-365到Gly的单个氨基酸变化。该患者在替代治疗期间也产生了IX因子抗体，这表明在血友病B患者中，IX因子基因的缺失对于抗体的产生是不必要的。 The levels of plasma factor IX antigen in the patients ranged from 40% to 100% except for IXDreihacken (Arg248Gln), in which case it was approximately 4% of normal. The Ser365Gly and Ser365Ile mutants are nonfunctional because of lack of the active site serine residue. Mutant Asp364His is inactive because it cannot form the hydrogen bond between the carboxylate group of Asp-364 and the alpha-amino group of Val-181 generated after activation. As observed in other homologous serine proteases, this hydrogen bond is essential for maintaining the correct active site conformation in normal factor IXa (IXaN). Purified Arg248Gln had approximately 41% and Glu245Val had approximately 17% of the activity of normal factor IX (IXN) in a partial thromboplastin time (aPTT) assay. In immunodot blot experiments, the isolated Glu245Val mutant did and the Arg248Gln mutant did not bind to an anti-IXN monoclonal antibody that has been shown previously to inhibit the interaction of factor VIIIa with factor IXaN. We have recently shown that a high-affinity calcium binding site exists in the protease domain of IXN; among the proposed Ca(2+)-binding ligands is the carboxyl group of Glu-245. Further, a part of the epitope for the above antibody was shown to be contained in the 231 to 265 residue segment of factor IX.(ABSTRACT TRUNCATED AT 400 WORDS)