Rivas G, Fernández J A, Minton A P
Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Cientificas, 28006 Madrid, Spain.
Proc Natl Acad Sci U S A. 2001 Mar 13;98(6):3150-5. doi: 10.1073/pnas.051634398.
Recent measurements of sedimentation equilibrium and sedimentation velocity have shown that the bacterial cell division protein FtsZ self-associates to form indefinitely long rod-like linear aggregates in the presence of GDP and Mg(2+). In the present study, the newly developed technique of non-ideal tracer sedimentation equilibrium was used to measure the effect of high concentrations-up to 150 g/liter-of each of two inert "crowder" proteins, cyanmethemoglobin or BSA, on the thermodynamic activity and state of association of dilute FtsZ under conditions inhibiting (-Mg(2+)) and promoting (+Mg(2+)) FtsZ self-association. Analysis of equilibrium gradients of both FtsZ and crowder proteins indicates that, under the conditions of the present experiment, FtsZ interacts with each of the two crowder proteins essentially entirely via steric repulsion, which may be accounted for quantitatively by a simple model in which hemoglobin, albumin, and monomeric FtsZ are modeled as effective spherical hard particles, and each oligomeric species of FtsZ is modeled as an effective hard spherocylinder. The functional dependence of the sedimentation of FtsZ on the concentrations of FtsZ and either crowder indicates that, in the presence of high concentrations of crowder, both the weight-average degree of FtsZ self-association and the range of FtsZ oligomer sizes present in significant abundance are increased substantially.
近期对沉降平衡和沉降速度的测量表明，细菌细胞分裂蛋白FtsZ在GDP和Mg(2+)存在的情况下会自我缔合，形成无限长的棒状线性聚集体。在本研究中，采用新开发的非理想示踪剂沉降平衡技术，来测量两种惰性“拥挤”蛋白（氰化高铁血红蛋白或牛血清白蛋白）中每一种在高达150克/升的高浓度下，对在抑制（-Mg(2+)）和促进（+Mg(2+)）FtsZ自我缔合的条件下稀释的FtsZ的热力学活性和缔合状态的影响。对FtsZ和拥挤蛋白的平衡梯度分析表明，在本实验条件下，FtsZ与两种拥挤蛋白中的每一种基本上完全通过空间排斥相互作用，这可以通过一个简单模型进行定量解释，在该模型中，血红蛋白、白蛋白和单体FtsZ被模拟为有效的球形硬颗粒，而FtsZ的每个寡聚体物种被模拟为有效的硬球柱体。FtsZ沉降对FtsZ和任一拥挤蛋白浓度的功能依赖性表明，在高浓度拥挤蛋白存在的情况下，FtsZ自我缔合的重均程度和大量存在的FtsZ寡聚体大小范围都显著增加。
