Alteration of membrane physicochemical properties by two factors for membrane protein integration
Alteration of membrane physicochemical properties by two factors for membrane protein integration
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膜蛋白整合的两个因素改变膜理化性质
DOI：
10.1016/j.bpj.2019.05.014
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发表时间：
2019
期刊：
影响因子：
--
通讯作者：
Shimamoto K.
中科院分区：
文献类型：
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作者：
Nomura K;Yamaguchi T;Mori S;Fujikawa K;Nishiyama K;Shimanouchi T;Tanimoto Y;Morigaki K;Shimamoto K.
在膜蛋白的新生链从核糖体隧道中出现后，蛋白质被整合到细胞膜中。这一过程是由一系列蛋白质分子装置控制的，如信号识别颗粒和Sec translocons。除了这些蛋白质，我们发现了两个内源性成分调节膜蛋白整合在内膜ofEscherichia coli。该整合被二酰基甘油（DAG）阻断，而该阻断被称为膜蛋白整合酶（MPIase）的糖脂解除。在这里，我们研究了这些整合阻断和整合促进因素的影响，通过固态核磁共振和荧光测量的膜脂的物理化学性质。这些因素对膜形态没有破坏性影响，因为膜保持其层状结构，并且在DAG和/或MPIase以其有效浓度存在下不融合。我们接下来关注膜的灵活性。DAG不影响膜表面的流动性，而MPIase中的糖链是高度移动的，并增强了膜脂质头基的灵活性。与合成MPIase类似物的比较揭示了长糖链对膜性质的影响。膜内的酰基链顺序增加DAG，而增加的MPIase的加入被取消。MPIase还使膜脂质包装松散。针对跨双层运动，MPIase减少了DAG的快速翻转运动。另一方面，MPIase不能补偿DAG减少的侧向扩散。这些结果表明，通过操纵膜脂质动力学，DAG抑制蛋白质接触内膜，而MPIase的柔性长糖链增加了膜和蛋白质之间相互作用的机会，导致新形成的蛋白质的膜整合。
After a nascent chain of a membrane protein emerges from the ribosomal tunnel, the protein is integrated into the cell membrane. This process is controlled by a series of proteinaceous molecular devices, such as signal recognition particles and Sec translocons. In addition to these proteins, we discovered two endogenous components regulating membrane protein integration in the inner membrane ofEscherichia coli. The integration is blocked by diacylglycerol (DAG), whereas the blocking is relieved by a glycolipid named membrane protein integrase (MPIase). Here, we investigated the influence of these integration-blocking and integration-promoting factors on the physicochemical properties of membrane lipids via solid-state NMR and fluorescence measurements. These factors did not have destructive effects on membrane morphology because the membrane maintained its lamellar structure and did not fuse in the presence of DAG and/or MPIase at their effective concentrations. We next focused on membrane flexibility. DAG did not affect the mobility of the membrane surface, whereas the sugar chain in MPIase was highly mobile and enhanced the flexibility of membrane lipid headgroups. Comparison with a synthetic MPIase analog revealed the effects of the long sugar chain on membrane properties. The acyl chain order inside the membrane was increased by DAG, whereas the increase was cancelled by the addition of MPIase. MPIase also loosened the membrane lipid packing. Focusing on the transbilayer movement, MPIase reduced the rapid flip-flop motion of DAG. On the other hand, MPIase could not compensate for the diminished lateral diffusion by DAG. These results suggest that by manipulating the membrane lipids dynamics, DAG inhibits the protein from contacting the inner membrane, whereas the flexible long sugar chain of MPIase increases the opportunity for interaction between the membrane and the protein, leading to membrane integration of the newly formed protein.