FIRST STEP OF HEME BIOSYNTHESIS IN MAMMALS

我们的长期目标是理解5- 氨基酮丙酸合成酶(ALAS)，包括酶和基因 水平，在分化过程中血红素生物合成的调节 红血球。唉，这是第一步，也是速度限制的第一步 血红素的生物合成，甘氨酸和磷脂酰胆碱依赖的反应 琥珀酰辅酶A生成氨基乙酰丙酸、辅酶A和二氧化碳。唉，唉！ 合成虽然无处不在，但主要发生在 红细胞和肝细胞，其中需求更大，因为 血红蛋白和细胞色素P-450的合成。 表达了红系特异的ALAS亚型(ALAS-E) 伴随着细胞的分化和成熟 红系细胞。最近，一组杂合子的点突变 在ALAS-E酶的催化域中已被发现 引起人类遗传性疾病X连锁铁粒母细胞贫血 (XLSA)。ALAS-的分子机理表征 催化反应和对基因表达的调控 ALAS-E基因是设计XLSA改进治疗方法的关键 患者和/或改善对高危家庭成员的诊断。 预计未来四年的研究将使用化学物质， 生化、物理和分子生物学方法 解决三个主要的具体目标：i)确定K313在 哺乳动物红系ALAS催化的反应；II)鉴定 PLP中甘氨酸环的重要功能残基 ALAS的辅因子结合部位；以及iii)评估转录 哺乳动物红系alas(Alas)基因的调控。 这些研究的结果将提供第一个表征 从分子水平研究ALAS的功能和作用机制 将阐明调控机制(S)的表达 ALAS-E在红细胞分化中的作用。值得注意的是，他们将 为已有的解释提供框架 发现与XLSA相关的ALAS-E基因突变。

The long term objective is to understand the role of 5- aminolevulinate synthase (ALAS), both at the enzyme and gene levels, in the regulation of heme biosynthesis in differentiating erythrocytes. ALAS catalyzes the first and rate limiting step in heme biosynthesis, the PLP-dependent reaction of glycine and succinyl-CoA to yield aminolevulinic acid, CoA and CO2. ALAS synthesis, although ubiquitous, occurs predominately in erythrocytes and hepatocytes, where demands are greater because of the synthesis of hemoglobin and cytochrome P-450, respectively. The erythroid-specific isoform of ALAS (ALAS-E) is expressed concomitantly with the differentiation and maturation of the erythroid cells. Recently a heterozygous group of point mutations in the catalytic domain of the ALAS-E enzyme has been found to cause the human genetic disorder X-linked sideroblastic anemia (XLSA). Characterization of the molecular mechanisms of the ALAS- catalyzed reaction and of the regulation of the expression of the ALAS-E gene are essential to design improved therapies for XLSA patients and/or for improved diagnosis for at-risk family members. Studies projected for the next four years will utilize chemical, biochemical, physical and molecular biological approaches to address three major specific aims: i) to define the role of K313 in the mammalian erythroid ALAS-catalyzed reaction; ii) to identify the functionally important residues of the glycine loop in the PLP cofactor binding site of ALAS; and iii) to evaluate transcriptional regulation of the mammalian erythroid ALAS (ALAS) gene. Results from these studies will provide the first characterization of the function and mechanism of ALAS at the molecular level and will elucidate the regulatory mechanism(s) of expression of the ALAS-E in differentiation erythrocytes. Significantly, they will provide the framework for the interpretation of the already identified ALAS-E genetic mutations associated with XLSA.