Global Proteomic Analysis Reveals an Exclusive Role of Thylakoid Membranes in Bioenergetics of a Model Cyanobacterium
Global Proteomic Analysis Reveals an Exclusive Role of Thylakoid Membranes in Bioenergetics of a Model Cyanobacterium
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DOI：
10.1074/mcp.m115.057240
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发表时间：
2016-06-01
影响因子：
7
通讯作者：
Pakrasi, Himadri B.
中科院分区：
文献类型：
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作者：
Liberton, Michelle;Saha, Rajib;Pakrasi, Himadri B.
蓝藻是具有高度分化的膜系统的光合作用微生物。这些生物体包括外膜、质膜和内部类囊体膜系统，光合作用和呼吸机制位于类囊体膜内部。这种膜系统的区隔和分化的存在对蓝藻细胞在蛋白质组织和分布到正确的膜系统方面提出了许多挑战。蛋白质组学研究长期以来一直试图确定蓝藻不同膜系统的组成，到目前为止，大约有450种不同的蛋白质被归因于质膜或类囊体膜。考虑到这些膜的复杂性，还有更多的蛋白质有待鉴定，需要一个全面的质膜和类囊体膜蛋白目录。在此，我们描述了集胞藻中635个差异定位蛋白的鉴定。其中459个蛋白定位于质膜，176个蛋白定位于类囊体膜。令人惊讶的是，我们发现质膜中鉴定的独特蛋白质的数量是类囊体膜的2.5倍以上。这表明类囊体膜的蛋白质组成比质膜更均匀，这与质膜在包括蛋白质运输和营养输入在内的不同细胞过程中的作用一致，而类囊体膜在细胞能量学中的作用更为特殊。因此，我们的数据清楚地定义了两个具有不同功能的膜系统。总体而言，聚球藻6803的质膜和类囊体膜的蛋白质组成分别与大肠杆菌的质膜和拟南芥叶绿体的类囊体膜非常相似。因此，集胞菌6803可以被描述为一种革兰氏阴性细菌，具有额外的内膜系统，以满足细胞的能量需求。
Cyanobacteria are photosynthetic microbes with highly differentiated membrane systems. These organisms contain an outer membrane, plasma membrane, and an internal system of thylakoid membranes where the photosynthetic and respiratory machinery are found. This existence of compartmentalization and differentiation of membrane systems poses a number of challenges for cyanobacterial cells in terms of organization and distribution of proteins to the correct membrane system. Proteomics studies have long sought to identify the components of the different membrane systems in cyanobacteria, and to date about 450 different proteins have been attributed to either the plasma membrane or thylakoid membrane. Given the complexity of these membranes, many more proteins remain to be identified, and a comprehensive catalogue of plasma membrane and thylakoid membrane proteins is needed. Here we describe the identification of 635 differentially localized proteins in Synechocystis sp. PCC 6803 by quantitative iTRAQ isobaric labeling; of these, 459 proteins were localized to the plasma membrane and 176 were localized to the thylakoid membrane. Surprisingly, we found over 2.5 times the number of unique proteins identified in the plasma membrane compared with the thylakoid membrane. This suggests that the protein composition of the thylakoid membrane is more homogeneous than the plasma membrane, consistent with the role of the plasma membrane in diverse cellular processes including protein trafficking and nutrient import, compared with a more specialized role for the thylakoid membrane in cellular energetics. Thus, our data clearly define the two membrane systems with distinct functions. Overall, the protein compositions of the Synechocystis 6803 plasma membrane and thylakoid membrane are quite similar to that of the plasma membrane of Escherichia coli and thylakoid membrane of Arabidopsis chloroplasts, respectively. Synechocystis 6803 can therefore be described as a Gram-negative bacterium with an additional internal membrane system that fulfills the energetic requirements of the cell.