Architecture of the bacterial divisome.

所有类型的细胞都需要生长和分裂才能生存。细菌是所有生命形式中最原始、最古老的一种，它的分裂机制相对简单，但其分裂过程却受到严格控制和协调。关键步骤包括细胞DNA的复制，这样细胞的每个拷贝都有一个相同的基因组拷贝，即生命的蓝图。这两个基因组的拷贝必须分开，这样当母细胞和子细胞最终分离成为独立的实体时，它们就不会纠缠在一起，每个细胞都有相同的基因组拷贝。分裂过程通常发生在分裂细胞的中心，一种被称为z环的分子机器就像一条皮带，在细胞中间越来越紧，直到完全闭合，将子细胞从母细胞中分离出来。想象一个小气球，用拇指和食指夹住。当食指像钳子一样弯曲拇指时，空气被挤进气球的两半。当食指和拇指之间没有空隙时，每个气球的一半，一个在你的手掌上，一个在你的手指上，是相同的体积。随着z环收紧，由短肽片段交联的碳水化合物链组成的肽聚糖保护层必须重新生成并沉积在细胞表面。这一作用必须与分裂过程的各个方面协调一致，否则细胞膜就会裸露，容易破裂，导致细胞死亡。这一建议涉及到z环闭合的调节是如何与肽聚糖合成协调的，以及一种被称为EzrA的关键蛋白所起的确切作用。这些活动是由一种称为分裂体的多蛋白组合协调的，它将z环与肽聚糖合成联系起来，但其方式尚不清楚。我们最近已经解决了以斯拉蛋白的结构，它与一类被称为谱蛋白的蛋白质惊人地相似，在动物中，谱蛋白被用来将膜嵌入的蛋白质连接到细胞骨架上。细胞骨架是在包括细菌在内的许多细胞类型的细胞质膜内表面发现的一种形状界定结构，由不同的蛋白质组成，包括肌动蛋白和微管蛋白。细菌细胞骨架还包括肌动蛋白和微管蛋白型蛋白，后者是可收缩z环的关键成分。因此，EzrA是spectrin的结构和功能同源物，因为它将细胞骨架与合成肽聚糖的膜内蛋白和其他膜内细胞分裂调节剂连接起来。在这个提议中，我们将确定EzrA与细胞骨架、分裂体的其他成员（包括产生肽聚糖的酶）和细胞分裂的关键调节因子相互作用的分子机制。该研究计划将使细菌和动物的细胞骨架之间的详细比较成为可能，目前主要集中在一种或两种蛋白质上。对两种细胞骨架之间的关系和差异的更深入的了解，也将有助于更好地理解多细胞生命形式从更简单的单细胞前身进化而来。

All cell types need to grow and to divide in order to survive. Bacteria, one of the most primitive and ancient of all life forms, divide by a relatively simple mechanism, but nonetheless in a process that is tightly controlled and co-ordinated. The key steps include the replication of the cell's DNA, so that each copy of the cell has an identical copy of the genome, the blueprint of life. The two copies of the genome then have to be separated so that they are not entangled when the mother and daughter cells finally separate to become discrete entities, each with an identical copy of the genome. The division process normally takes place at the centre of the dividing cell and a molecular machine called the Z-ring acts as a belt, constricting tighter and tighter across the middle of the cell until it closes completely, pinching off the daughter from the mother cell. Imagine a small balloon, grasped between thumb and forefinger. As the forefinger bends like a pincer against the thumb, air is squeezed into the two halves of the balloon. When there is no gap between forefinger and thumb, each of the balloon halves, one in the palm of your hand and one above your fingers, are the same volume. As the Z-ring tightens, a protective layer called peptidoglycan, made of strands of carbohydrate cross-linked by short peptide fragments, has to be made afresh and deposited on the surface of the cell. This action must be co-ordinated with all aspects of the division process, otherwise the cell membrane is left uncovered and is prone to rupture, causing death of the cell.This proposal concerns how the regulation of the closure of the Z-ring is co-ordinated with peptidoglycan synthesis, and the precise role played by a key protein known as EzrA. These activities are co-ordinated by a multi-protein assembly called the divisome, which links the Z-ring to peptidoglycan synthesis, but in a manner that is not yet understood. We have recently solved the structure of EzrA, which is surprisingly similar to a class of proteins called spectrins that, in animals, are used to link membrane-embedded proteins to the cytoskeleton. The cytoskeleton is a shape-defining structure found on the inside face of the cytoplasmic membrane in many cell types, including bacteria, comprising different proteins including actin and tubulin. The bacterial cytoskeleton also comprises actin and tubulin-type proteins, the latter of which is the key component of the contractile Z-ring. EzrA is therefore a structural and functional homologue of spectrin, as it acts to link the cytoskeleton to membrane-embedded proteins that synthesise peptidoglycan, and other membrane-embedded cell division regulators. In this proposal we will ascertain the molecular mechanisms used by EzrA to interact with the cytoskeleton, other members of the divisome, including the enzymes that generate peptidoglycan, and key regulators of cell division. The research program will enable for detailed comparisons to be made between the cytoskeletons of bacteria and of animals, which is currently focussed on one or two proteins. A greater understanding of the relationships and the differences between the two cytoskeletons will also provide a greater understanding of the evolution of multicellular life forms from their simpler, single-celled predecessors.