Human mitochondrial fatty acid synthase

描述（由申请人提供）：提出了新的令人信服的证据，表明人类线粒体含有酰基载体蛋白（ACP）依赖系统，用于丙二酰辅酶a合成脂肪酸。序列和功能分析表明，核编码的线粒体靶向脂肪酸合成酶（mitFAS）成分是类似于原核生物的脂肪酸合成酶的单个蛋白质，因此不同于真核生物的细胞质脂肪酸合成酶，在真核生物中，所有的酶都存在于单个多肽链上。mitFAS ACP与呼吸链复合体1有关。最近在真菌中也发现了类似的系统；这种mitFAS系统的破坏导致呼吸缺陷表型，这表明确定这种“新的”代谢途径是否也可能在人类线粒体功能中发挥关键作用是及时的。该提案有三个目标：鉴定、分离和表征人类mitFAS的单个成分，鉴定它们产生的产物，并评估线粒体功能途径的重要性。

DESCRIPTION (provided by applicant): New, compelling evidence is presented indicating that human mitochondria contain an acyl carrier protein (ACP)-dependent system for synthesis of fatty acids from malonyl-CoA. Sequence and functional analyses indicate that nuclear-encoded, mitochondrially-targeted fatty acid synthase (mitFAS) components are individual proteins resembling the FASs of prokaryotes and thus differ from the eukaryotic cytosolic FASs, in which all of the enzymes are present on a single polypeptide chain. The mitFAS ACP is associated with complex 1 of the respiratory chain. A similar system has recently been described in fungi; disruption of this mitFAS system results in respiratory deficient phenotypes, indicating that it is timely to determine whether this 'new' metabolic pathway may also play a critical role in human mitochondrial function. The proposal has three objectives: to identify, isolate and characterize individual components of the human mitFAS, to identify the products they generate and to assess the significance of the pathway to mitochondrial function. (1) Candidate mitFAS components, identified by BLAST searches of the human sequence database, will be cloned, expressed, purified and their substrate specificities determined. Confirmation that they are authentic mitochondrial proteins will be sought by demonstrating that mitFAS-green fluorescent-protein chimeras expressed in human cells are transported to the mitochondria only when putative N-terminal targeting sequences are present. (2) The products formed by the mitFAS pathway will be characterized by exposing permeabolized mitochondria to various radiolabeled substrates and identifying the products chromatographically. Particular attention will be paid to the possibility that the pathway generates octanoate, the precursor of lipoic acid, and/or long chain fatty acids that could be used in the biosynthesis of mitochondrial phospholipids. (3) The significance of the pathway to mitochondrial function will be assessed by silencing expression of mitFAS components, through RNA-mediated interference, and determining the effect on cellular morphology, mitochondrial respiratory capacity and mitochondrial phospholipid composition. Failure in mitochondrial function has been implicated in the pathogenesis of late developing neurodegenerative disorders such as Parkinson's, Alzheimer's, and Huntington's diseases, yet the role of many mitochondrial proteins is still unknown. Elucidation of the role of the mitFAS system in mitochondrial function may aid in understanding the etiology of these disorders.