Department of Molecular Medicine, Morsani College of Medicine, University of South Florida, Tampa, FL 33612, USA.
Department of Chemistry, College of Arts and Sciences, University of South Florida, Tampa, FL 33612, USA.
Int J Mol Sci. 2018 Jun 28;19(7):1899. doi: 10.3390/ijms19071899.
Biosynthesis of heme represents a complex process that involves multiple stages controlled by different enzymes. The first of these proteins is a pyridoxal 5′-phosphate (PLP)-dependent homodimeric enzyme, 5-aminolevulinate synthase (ALAS), that catalyzes the rate-limiting step in heme biosynthesis, the condensation of glycine with succinyl-CoA. Genetic mutations in human erythroid-specific ALAS (ALAS2) are associated with two inherited blood disorders, X-linked sideroblastic anemia (XLSA) and X-linked protoporphyria (XLPP). XLSA is caused by diminished ALAS2 activity leading to decreased ALA and heme syntheses and ultimately ineffective erythropoiesis, whereas XLPP results from “gain-of-function” ALAS2 mutations and consequent overproduction of protoporphyrin IX and increase in Zn-protoporphyrin levels. All XLPP-linked mutations affect the intrinsically disordered C-terminal tail of ALAS2. Our earlier molecular dynamics (MD) simulation-based analysis showed that the activity of ALAS2 could be regulated by the conformational flexibility of the active site loop whose structural features and dynamics could be changed due to mutations. We also revealed that the dynamic behavior of the two protomers of the ALAS2 dimer differed. However, how the structural dynamics of ALAS2 active site loop and C-terminal tail dynamics are related to each other and contribute to the homodimer asymmetry remained unanswered questions. In this study, we used bioinformatics and computational biology tools to evaluate the role(s) of the C-terminal tail dynamics in the structure and conformational dynamics of the murine ALAS2 homodimer active site loop. To assess the structural correlation between these two regions, we analyzed their structural displacements and determined their degree of correlation. Here, we report that the dynamics of ALAS2 active site loop is anti-correlated with the dynamics of the C-terminal tail and that this anti-correlation can represent a molecular basis for the functional and dynamic asymmetry of the ALAS2 homodimer.
血红素的生物合成是一个复杂的过程，涉及多个由不同酶控制的阶段。这些蛋白质中的第一种是吡哆醛 5′-磷酸（PLP）依赖性同源二聚体酶，5-氨基酮戊酸合酶（ALAS），它催化血红素生物合成的限速步骤，即甘氨酸与琥珀酰辅酶 A 的缩合。人类红细胞特异性 ALAS（ALAS2）的遗传突变与两种遗传性血液疾病有关，X 连锁铁幼粒细胞性贫血（XLSA）和 X 连锁原卟啉症（XLPP）。XLSA 是由于 ALAS2 活性降低导致 ALA 和血红素合成减少，最终导致无效的红细胞生成，而 XLPP 是由于“获得功能”的 ALAS2 突变和随后原卟啉 IX 的过度产生以及 Zn-原卟啉水平的增加所致。所有与 XLPP 相关的突变都影响 ALAS2 的无规则卷曲的 C 末端尾巴。我们之前的基于分子动力学（MD）模拟的分析表明，ALAS2 的活性可以通过活性位点环的构象灵活性来调节，其结构特征和动力学可能由于突变而改变。我们还揭示了 ALAS2 二聚体的两个亚基的动态行为不同。然而，ALAS2 活性位点环的结构动力学和 C 末端尾巴动力学如何相互关联并有助于同源二聚体的不对称性仍然是悬而未决的问题。在这项研究中，我们使用生物信息学和计算生物学工具来评估 C 末端尾巴动力学在鼠类 ALAS2 同源二聚体活性位点环的结构和构象动力学中的作用。为了评估这两个区域之间的结构相关性，我们分析了它们的结构位移并确定了它们的相关性程度。在这里，我们报告说 ALAS2 活性位点环的动力学与 C 末端尾巴的动力学呈反相关，这种反相关可以代表 ALAS2 同源二聚体的功能和动态不对称性的分子基础。
