ENZYMATIC DEFECT IN X-LINKED SIDEROBLASTIC ANEMIA - MOLECULAR EVIDENCE FOR ERYTHROID DELTA-AMINOLEVULINATE SYNTHASE DEFICIENCY
ENZYMATIC DEFECT IN X-LINKED SIDEROBLASTIC ANEMIA - MOLECULAR EVIDENCE FOR ERYTHROID DELTA-AMINOLEVULINATE SYNTHASE DEFICIENCY
复制标题
DOI：
10.1073/pnas.89.9.4028
复制
发表时间：
1992-05-01
影响因子：
11.1
通讯作者：
BISHOP, DF
中科院分区：
文献类型：
--
作者：
COTTER, PD;BAUMANN, M;BISHOP, DF
最近，编码红细胞特异性δ-氨基乙酰丙酸合酶的人类基因被定位于染色体区域Xp 21-Xq 21，确定该基因为引起“X连锁”铁粒幼细胞性贫血的酶缺陷的逻辑候选者。为了研究这一假设，11外显子编码区的δ-氨基乙酰丙酸合成酶基因扩增和测序从一个30岁的中国男性与吡哆醇反应形式的X-连锁铁粒幼细胞性贫血。在外显子9高度保守区域的密码子471处发现一个T -> A转换，导致Ile -> Asn取代。该突变中断了连续的疏水残基，并被预测将β-折叠结构的区域转化为无规卷曲结构。正常和突变体cDNA的蛋白质表达揭示了突变体构建体表达低水平的酶活性，其需要比正常酶更高浓度的吡哆醛5 '-磷酸来实现最大活化。氨基酸取代发生在含有假定的吡哆醛5 '-磷酸结合位点的外显子中，可能是辅因子催化δ-氨基乙酰丙酸形成的能力降低的原因。
Recently, the human gene encoding erythroid-specific delta-aminolevulinate synthase was localized to the chromosomal region Xp21-Xq21, identifying this gene as the logical candidate for the enzymatic defect causing "X-linked" sideroblastic anemia. To investigate this hypothesis, the 11 exonic coding regions of the delta-aminolevulinate synthase gene were amplified and sequenced from a 30-year-old Chinese male with a pyridoxine-responsive form of X-linked sideroblastic anemia. A single T --> A transition was found in codon 471 in a highly conserved region of exon 9, resulting in an Ile --> Asn substitution. This mutation interrupted contiguous hydrophobic residues and was predicted to transform a region of beta-sheet structure to a random-coil structure. Prokaryotic expression of the normal and mutant cDNAs revealed that the mutant construct expressed low levels of enzymatic activity that required higher concentrations of pyridoxal 5'-phosphate to achieve maximal activation than did the normal enzyme. The amino acid substitution occurred in the exon containing the putative pyridoxal 5'-phosphate binding site and may account for the reduced ability of the cofactor to catalyze the formation of delta-aminolevulinic acid.