Mikrobiologie, Fakultät für Biologie, Universität Freiburg, Schänzle Strasse 1, 79104 Freiburg, Germany.
Mol Microbiol. 2010 Dec;78(5):1145-58. doi: 10.1111/j.1365-2958.2010.07395.x. Epub 2010 Oct 8.
Like many bacteria, Bacillus subtilis cells contain three actin-like MreB proteins. We show that the three paralogues, MreB, Mbl and MreBH, have different filament architectures in a heterologous cell system, and form straight filaments, helices or ring structures, different from the regular helical arrangement in B. subtilis cells. However, when coexpressed, they colocalize into a single filamentous helical structure, showing that the paralogues influence each other's filament architecture. Ring-like MreBH structures can be converted into MreB-like helical filaments by a single point mutation affecting subunit contacts, showing that MreB paralogues feature flexible filament arrangements. Time-lapse and FRAP experiments show that filaments can extend as well as shrink at both ends, and also show internal rearrangement, suggesting that filaments consist of overlapping bundles of shorter filaments that continuously turn over. Upon induction in Escherichia coli cells, B. subtilis MreB (BsMreB) filaments push the cells into strikingly altered cell morphology, showing that MreB filaments can change cell shape. E. coli cells with a weakened cell wall were ruptured upon induction of BsMreB filaments, suggesting that the bacterial actin orthologue may exert force against the cell membrane and envelope, and thus possibly plays an additional mechanical role in bacteria.
枯草芽孢杆菌细胞中像许多细菌一样含有三种肌动蛋白样 MreB 蛋白。我们发现，这三种蛋白（MreB、Mbl 和 MreBH）在异源细胞系统中具有不同的丝状体结构，形成直丝、螺旋或环结构，与枯草芽孢杆菌细胞中的规则螺旋排列不同。然而，当它们共表达时，它们会共定位到一个单一的丝状螺旋结构中，这表明这些旁系同源物会相互影响其丝状体结构。通过影响亚基接触的单点突变，环状的 MreBH 结构可以转化为类似于 MreB 的螺旋丝，表明 MreB 旁系同源物具有灵活的丝状体排列。延时和 FRAP 实验表明，丝状体可以在两端延伸和收缩，并且还显示出内部重排，这表明丝状体由重叠的短丝束组成，这些短丝束不断地翻转。在大肠杆菌细胞中诱导表达时，枯草芽孢杆菌 MreB（BsMreB）丝体会将细胞推挤成明显改变的细胞形态，表明 MreB 丝状体可以改变细胞形状。当诱导 BsMreB 丝状体时，细胞壁较弱的大肠杆菌细胞会破裂，这表明细菌肌动蛋白同源物可能会对细胞膜和包膜施加力，因此可能在细菌中发挥额外的机械作用。
