Phospholipids and Mitochondrial Function

描述（由申请人提供）：心磷脂（CL）是正常线粒体能量代谢的必需磷脂，因此其水平的生理和病理扰动导致线粒体结构、功能和组装的改变。CL是线粒体能量转导系统的大多数组分的组成部分。心肌功能障碍和细胞凋亡与Barth综合征、衰老、缺血/再灌注和心力衰竭中的CL水平异常相关。酿酒酵母突变体（crd 1？）缺乏CL，但含有其前体磷脂酰甘油（PG），或突变体（PGS 1？）缺乏PG和CL的细胞分别显示出与PG和CL水平降低或不能产生PG和CL的哺乳动物细胞相似的表型。因此，酵母是研究这些脂质在线粒体功能中作用的一个很好的模型系统。酵母PGS 1？CRD1？突变体导致了两个发现，这是拟议研究的基础。(1)翻译阻遏物，结合5'的翻译起始位点的mRNA的亚基4（Cox 4p）的线粒体电子传递链组分细胞色素c氧化酶（复合物IV）的特异性激活或合成响应改变线粒体磷脂组成的PGS 1？变种人研究建议从遗传学和生物化学的角度来确定这一新的线粒体应激反应途径的组成部分和机制。(2)复合物IV和复合物III（细胞色素bc 1）形成一个III 2 IV 2的超复合物，动力学行为作为一个单一的单位“cardasome”，这是建立通过使用crd 1？突变体特异性依赖于CL。实验提出，以确定磷脂的化学计量在个别的复合物III和IV和在III 2 IV 2 supercomplex和CL的位置内后者所需的形成和稳定的supercomplex。一个3-D结构的III 2 IV 2超复合物已被确定通过负染色电子显微镜和单颗粒分析，这将使用冷冻电子显微镜，以建立复杂的III和IV是如何组织在超复合物。磷脂分析和结构数据将被整合，以建立CL是如何参与“胶合”在一起的超复合物组件。确定PG和CL在正常线粒体功能中的作用将揭示这些脂质减少的生理和病理状态下细胞功能障碍的分子基础。

DESCRIPTION (provided by applicant): Cardiolipin (CL) is an essential phospholipid for normal mitochondrial energy metabolism so that physiological and pathological perturbations in its levels result in alterations in the structure, function and assembly of mitochondria. CL is an integral part of most of the components of the mitochondrial energy transducing system. Myocardial dysfunction and apoptosis are associated with abnormal CL levels in Barth Syndrome, aging, ischemia/reperfusion, and heart failure. Saccharomyces cerevisiae mutants (crd1?) lacking CL, but containing its precursor phosphatidylglycerol (PG), or mutants (pgs1?) lacking both PG and CL display similar phenotypes to mammalian cells with reduced PG and CL levels or the inability to make PG and CL, respectively. Therefore, yeast is an excellent model system to study their role of these lipids in mitochondrial function. Studies of yeast pgs1? and crd1? mutants led to two findings that are the basis for the proposed studies. (1) Translation repressors that bind 5' of the translation initiation site on mRNA for subunit 4 (Cox4p) of the mitochondrial electron transport chain component cytochrome c oxidase (Complex IV) are specifically activated or synthesized in response to altered mitochondrial phospholipid composition in pgs1? mutants. Studies are proposed to genetically and biochemically define the components and mechanism of this novel mitochondrial stress response pathway. (2) Complex IV and Complex III (cytochrome bc1) form a III2IV2 supercomplex that kinetically behaves as a single unit "respirasome", which was established by using a crd1? mutant to be specifically dependent on CL. Experiments are proposed to determine the phospholipid stoichiometry in the individual Complexes III and IV and in the III2IV2 supercomplex and the location of CL within the latter required for formation and stabilization of the supercomplex. A 3-D structure of the III2IV2 supercomplex has been determined by negative stain-electron microscopy and single particle analysis, which will be refined using cryoelectron microscopy to establish how Complex III and IV are organized in the supercomplex. Phospholipid analysis and structural data will be integrated to establish how CL is involved in "gluing" together the supercomplex components. Defining the roles PG and CL play in normal mitochondrial function will shed light on the molecular basis for cellular dysfunction in physiological and pathological states where these lipids are reduced.