How Does Polymerization Regulate Human Acetyl-CoA Carboxylase 1?
How Does Polymerization Regulate Human Acetyl-CoA Carboxylase 1?
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DOI：
10.1021/acs.biochem.8b00881
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发表时间：
2018-09
期刊：
影响因子：
2.9
通讯作者：
Jia Wei;L. Tong
中科院分区：
文献类型：
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作者：
Jia Wei;L. Tong
乙酰辅酶a羧化酶（ACCs）是生物素依赖性酶，催化乙酰辅酶a羧化生成丙二酰辅酶a，丙二酰辅酶a被用作生产脂肪酸和聚酮的二碳结构单元。1在人类中，ACC1存在于脂肪生成组织中，控制着脂肪酸新生生物合成的第一步和限速步骤，而ACC2存在于肌肉和肝脏中，控制着线粒体中脂肪酸氧化的抑制。ACC活性在转录、翻译和翻译后水平上都受到严格的调控，人类ACC1的调控包括磷酸化抑制、丙二酰辅酶a的产物抑制、柠檬酸的前反馈激活和棕榈酰辅酶a的反馈抑制。特别是，近50年前，人们观察到柠檬酸盐促进动物ACC1细丝的形成，尽管这种聚合如何激活ACC1的分子基础尚不清楚。acc具有两种独立的催化活性，生物素羧化酶（BC）和羧基转移酶（CT），生物素与生物素羧基载体蛋白（BCCP）相连。大多数真核生物acc为~ 250 kDa，单链，多结构域酶，功能为二聚体和更高的低聚物。BC结构域位于N端，其次是BT （BC - CT相互作用）和BCCP结构域，CT（具有N和C结构域）位于C端（图1a）。中心区域是真核acc所特有的。关于acc的BC、CT和BCCP组件有广泛的结构知识。酵母ACC的结构提供了对真核ACC全酶的第一个分子见解，它与人类ACC具有50%的序列一致性。500 kDa酵母ACC二聚体呈四分之一圆盘形状，BC二聚体靠近圆盘中心，CT二聚体位于边缘（图1b）。ACC的中心区域（ACC central， AC）包含5个结构域，AC1 ~ AC5，它们位于结构的两侧，对BC或CT活性位点没有直接贡献。这个区域可能起到支架的作用，将两个活性位点固定在催化的正确位置。两个活性位点相距80 Å， BCCP及其生物素在催化过程中在它们之间移位（摆动结构域模型）。ACC中的CT二聚体在两个单体之间有广泛的界面。相比之下，BC二聚体不太稳定，是ACC二聚体的弱链接。事实上，单独的BC结构域在活性位点有广泛的构象变化，使其在催化上不活跃，以及在二聚体界面，形成一个口袋，允许识别ACC磷酸化和小分子。2电镜研究表明，酵母ACC二聚体在典型的缓冲液中主要以连续的“开放”状态存在，其中BC二聚体被解离，3这些开放状态具有催化活性。有趣的是，柠檬酸盐促进了全酶的“封闭”、活性形式，尽管我们还不知道柠檬酸盐是否能激活酵母ACC。总的来说，这些数据证明了ACC全酶中大量的构象动力学，并提出了一个模型，其中磷酸化和抑制ACC的小分子促进了二聚体的开放形式，例如通过稳定BC单体（图2a）。3最近在柠檬酸盐存在下形成的去磷酸化的人ACC1丝（ACC1-柠檬酸丝）的低温电镜结构是该领域的一个重大突破。这也是一项技术上的绝技研究。
Acetyl-CoA carboxylases (ACCs) are biotin-dependent enzymes that catalyze the carboxylation of acetyl-CoA to generate malonyl-CoA, which is used as a two-carbon building block for producing fatty acids and polyketides. 1 In humans, ACC1 is found in lipogenic tissues and controls the first and rate-limiting step of de novo fatty acid biosynthesis, while ACC2 is found in muscles and liver and controls the inhibition of fatty acid oxidation in mitochondria. ACC activity is under tight regulations, at the transcriptional, translational, and posttranslational levels, and those for human ACC1 include inhibition by phosphorylation, product inhibition by malonyl-CoA, feedforward activation by citrate, and feedback inhibition by palmitoyl-CoA. Especially, citrate was observed to promote the formation of animal ACC1 filaments nearly 50 years ago, although the molecular basis of how this polymerization can activate ACC1 was not known. ACCs contain two separate catalytic activities, biotin carboxylase (BC) and carboxyltransferase (CT), with biotin linked to biotin carboxyl carrier protein (BCCP). 1 Most eukaryotic ACCs are∼ 250 kDa, single-chain, multidomain enzymes and function as dimers and higher oligomers. The BC domain is located at the N-terminus, followed by the BT (BC− CT interaction) and BCCP domains, and the CT (with N and C domains) is at the C-terminus (Figure 1 A). The central region is unique to eukaryotic ACCs. There is extensive structural knowledge on the BC, CT, and BCCP components of ACCs. 1 The first molecular insights into the eukaryotic ACC holoenzyme were provided by the structure of yeast ACC, 2 which shares 50% sequence identity with human ACC1. The 500 kDa yeast ACC dimer is in the shape of a quarter disk, with a BC dimer near the center of the disk and CT dimer at the edge (Figure 1 B). The central region of ACC (ACC central, AC) contains five domains, AC1− AC5, and they are located at the sides of the structure, with no direct contribution to BC or CT active sites. This region likely serves as a scaffold, holding the two active sites in the correct position for catalysis. The two active sites are separated by 80 Å, and BCCP and its biotin translocate between them during catalysis (swinging-domain model). 1The CT dimer in ACC has an extensive interface between the two monomers. In contrast, the BC dimer is less stable and is a weak link in the ACC dimer. In fact, the BC domain alone has extensive conformational changes in the active site, making it catalytically inactive, as well as in the dimer interface, creating a pocket that allows the recognition of ACC phosphorylation and small molecules. 2 Electron microscopy studies showed that the yeast ACC dimer primarily exists in a continuum of “open” states in a typical buffer, where the BC dimer is dissociated, 3 and these open states are catalytically inactive. Interestingly, citrate promotes the “closed”, active form of the holoenzyme, even though citrate is not known to activate yeast ACC. Overall, these data demonstrate substantial conformational dynamics in the ACC holoenzyme and suggest a model where phosphorylation and small molecules that inhibit ACC promote the open form of the dimer, for example by stabilizing the BC monomer (Figure 2 A). 3 The recent cryo-electron microscopy structure of dephosphorylated human ACC1 filament formed in the presence of citrate (ACC1-citrate filament) is a major breakthrough in the field. 4 It is also a tour de force study technologically,