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首页> 外文期刊>Journal of Molecular Biology >The monomeric, tetrameric, and fibrillar organization of Fib: the dynamic building block of the bacterial linear motor of Spiroplasma melliferum BC3.
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The monomeric, tetrameric, and fibrillar organization of Fib: the dynamic building block of the bacterial linear motor of Spiroplasma melliferum BC3.

机译：Fib的单体，四聚体和原纤维组织：螺旋螺旋体BC3细菌线性马达的动态构建基块。

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摘要

Spiroplasmas belong to the class Mollicutes, representing the minimal, free-living, and self-replicating forms of life. Spiroplasmas are helical wall-less bacteria and the only ones known to swim by means of a linear motor (rather than the near-universal rotary bacterial motor). The linear motor follows the shortest path along the cell's helical membranal tube. The motor is composed of a flat monolayered ribbon of seven parallel fibrils and is believed to function in controlling cell helicity and motility through dynamic, coordinated, differential length changes in the fibrils. The latter cause local perturbations of helical symmetry, which are essential for net directional displacement in environments with a low Reynolds number. The underlying fibrils' core building block is a circular tetramer of the 59-kDa protein Fib. The fibrils' differential length changes are believed to be driven by molecular switching of Fib, leading consequently to axial ratio and length changes in tetrameric rings. Using cryo electron microscopy, diffractometry, single-particle analysis of isolated ribbons, and sequence analyses of Fib, we determined the overall molecular organization of the Fib monomer, tetramer, fibril, and linear motor of Spiroplasma melliferum BC3 that underlies cell geometry and motility. Fib appears to be a bidomained molecule, of which the N-terminal half is apparently a globular phosphorylase. By a combination of reversible rotation and diagonal shift of Fib monomers, the tetramer adopts either a cross-like nonhanded conformation or a ring-like handed conformation. The sense of Fib rotation may determine the handedness of the linear motor and, eventually, of the cell. A further change in the axial ratio of the ring-like tetramers controls fibril lengths and the consequent helical geometry. Analysis of tetramer quadrants from adjacent fibrils clearly demonstrates local differential fibril lengths.
机译：螺旋体属于Mollicutes类，代表极简，自由生活和自我复制的生命形式。螺旋体是螺旋形无壁细菌，是唯一已知通过线性马达（而不是近乎通用的旋转细菌马达）游动的细菌。线性马达沿着细胞的螺旋膜管的最短路径。该马达由七个平行原纤维的扁平单层带组成，据信可通过原纤维的动态，协调，不同长度变化来控制细胞的螺旋度和运动性。后者引起螺旋对称的局部扰动，这对于低雷诺数的环境中的净方向位移至关重要。潜在的原纤维的核心构件是59 kDa蛋白Fib的环状四聚体。认为原纤维的不同长度变化是由Fib的分子转换驱动的，因此导致四聚环的轴向比和长度变化。使用冷冻电子显微镜，衍射法，分离的带的单颗粒分析和Fib的序列分析，我们确定了螺旋螺BC3的Fib单体，四聚体，原纤维和线性马达的整体分子结构，这是细胞几何结构和运动性的基础。 Fib似乎是一个双域分子，其N端一半显然是球状磷酸化酶。通过结合Fib单体的可逆旋转和对角位移，四聚体采用十字形的非手构型或环状的手形构型。 Fib旋转的感觉可以确定线性电动机的操纵性，并最终确定单元的操纵性。环状四聚体的轴向比率的进一步变化控制了原纤维的长度和随之而来的螺旋几何形状。对来自相邻原纤维的四聚体象限的分析清楚地表明了局部差异原纤维长度。

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