Molecular mechanism of cell curvature in the spiral-shaped bacterium Rhodospirillum rubrum

细菌表现出高度的细胞形状多样性，在大多数情况下，这是由肽聚糖细胞壁决定的。以往的工作表明，标准模式生物的典型杆状形态是由两个主要的肽聚糖生物合成复合体--伸长体和分裂体产生的。在这些复合体中，合成的、裂解的和调节的蛋白质被组合在一起，以协调地重塑肽聚糖层，以便分别产生细胞的圆柱形和球形元件。然而，建立更复杂的形态的潜在机制仍然知之甚少。常见杆状形状的广泛变化是弯曲或螺旋状的形态，这是由于内外曲率处杆状肽聚糖层的不同生长而引起的。弯曲的形状在细菌中很常见，而且似乎不同的谱系之间潜在的形状生成机制有根本的不同。然而，即使对于经过充分研究的系统，所确定的形状决定因素的确切作用模式仍然不清楚。在这里，我们建议研究螺旋形细菌红色红螺菌中细胞曲率的建立。在前期工作中，我们已经鉴定出一种新的与肽聚糖结合的外膜脂蛋白，PAPS，它在红色核杆菌细胞的外曲率处形成丝状结构，是其螺旋形态所必需的。PAPs在Rhodspirillaceae的成员中高度保守，Rhodspirillaceae是一个由大量弯曲和螺旋形物种组成的家族，这表明它是这一谱系中一个关键的细胞形状决定因素。我们建议结合细胞生物学、遗传学、生化和生物物理方法来揭示PAPs的功能。这些研究将为我们提供一种新的和广泛的细菌形状决定途径，从而大大加深我们对细菌细胞壁的生物合成和形态发生的理解。

Bacteria show a high diversity of cell shapes, which in most cases are determined by the peptidoglycan cell wall. Previous work has revealed that the prototypical rod-shaped morphologies of standard model organisms are generated by two major peptidoglycan biosynthetic complexes, the elongasome and the divisome. In these complexes, synthetic, lytic and regulatory proteins are combined to coordinately remodel the peptidoglycan layer in order to generate the cylindrical and spherical elements of the cell, respectively. However, the mechanisms underlying the establishment of more complex morphologies are still poorly understood. Widespread variations of the common rod shape are curved or spiral morphologies, which arise by differential growth of the rod-shaped peptidoglyan layer at the inner and outer curvature. Curved shapes are commonly found among bacteria, and it appears that the underlying shape-generating mechanisms differ fundamentally between different lineages. However, even for well-investigated systems, the precise modes of action of the shape determinants identified are still unclear. Here, we propose to study the establishment of cell curvature in the spiral-shaped bacterium Rhodospirillum rubrum. In preliminary work, we have identified a novel peptidoglycan-binding outer-membrane lipoprotein, PapS, which forms a filament-like structure at the outer curvature of the R. rubrum cell and is essential for its spiral morphology. PapS is highly conserved among the members of the Rhodospirillaceae, a family comprising a large number of curved and spiral-shaped species, suggesting that it represents a key cell shape determinant in this lineage. We propose to unravel the function of PapS using a combination of cell biological, genetic, biochemical and biophysical approaches. These studies will provide insight into a novel and widespread pathway of shape determination in bacteria and thus significantly further our understanding of bacterial cell wall biosynthesis and morphogenesis.