Cytoplasmic Protein Mobility in Osmotically Stressed Escherichia coli
Cytoplasmic Protein Mobility in Osmotically Stressed Escherichia coli
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DOI：
10.1128/jb.00536-08
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发表时间：
2009-01-01
影响因子：
3.2
通讯作者：
Weisshaar, James C.
中科院分区：
文献类型：
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作者：
Konopka, Michael C.;Sochacki, Kem A.;Weisshaar, James C.
球状蛋白质在细胞质中的易扩散是生物聚合物密集的，对正常的细胞生物化学活动和生长至关重要。值得注意的是，大肠杆菌在基本培养基中生长的外部渗透压范围很宽（0.03至1.8 μ l）。这种适应细胞的平均细胞质生物聚合物体积分数（）范围从0.10微升时的0.16到1.45微升时的0.36。对于在0.28 μ l下生长的细胞，使用NaCl或蔗糖作为外部渗压剂，通过等离子体渗透（突然渗透上移）获得类似的范围，之后唯一可用的细胞反应是细胞质水的被动损失。本实验测定了绿色荧光蛋白（D-GFP）在大肠杆菌胞质中的有效轴向扩散系数。大肠杆菌细胞作为一个功能的两个plastenized和适应的细胞。对于塑化细胞，中值D-GFP（D-GFP（m））从0.16增加到0.33，减少了70倍。与此形成鲜明对比的是，对于适应细胞，D-GFP（m）从0.16增加到0.36时仅减少2.1倍。显然，GFP扩散不是由单独决定的。通过与定量模型的比较，我们表明，数据不能解释拥挤理论。我们提出了这种令人惊讶的效果的可能的根本原因，并进一步的实验，这将有助于选择竞争的假设。恢复的能力，蛋白质扩散的细胞质后，plasma很可能是一个关键的决定因素的时间尺度的恢复增长。
Facile diffusion of globular proteins within a cytoplasm that is dense with biopolymers is essential to normal cellular biochemical activity and growth. Remarkably, Escherichia coli grows in minimal medium over a wide range of external osmolalities (0.03 to 1.8 osmol). The mean cytoplasmic biopolymer volume fraction () for such adapted cells ranges from 0.16 at 0.10 osmol to 0.36 at 1.45 osmol. For cells grown at 0.28 osmol, a similar range is obtained by plasmolysis (sudden osmotic upshift) using NaCl or sucrose as the external osmolyte, after which the only available cellular response is passive loss of cytoplasmic water. Here we measure the effective axial diffusion coefficient of green fluorescent protein (D-GFP) in the cytoplasm of E. coli cells as a function of for both plasmolyzed and adapted cells. For plasmolyzed cells, the median D-GFP (D-GFP(m)) decreases by a factor of 70 as increases from 0.16 to 0.33. In sharp contrast, for adapted cells, D-GFP(m) decreases only by a factor of 2.1 as increases from 0.16 to 0.36. Clearly, GFP diffusion is not determined by alone. By comparison with quantitative models, we show that the data cannot be explained by crowding theory. We suggest possible underlying causes of this surprising effect and further experiments that will help choose among competing hypotheses. Recovery of the ability of proteins to diffuse in the cytoplasm after plasmolysis may well be a key determinant of the time scale of the recovery of growth.