Piggy-backing the bacterial chromosome: positioning of protein complexes by chromosome segregation

当细胞分裂时，通常会产生一个合理的自身复制品。随着细胞的生长，它产生新的蛋白质，因此，在分裂之前，有理由假设它的蛋白质数量是初始细胞的两倍。当细胞分裂时，每个子细胞都需要一条染色体来制造这些蛋白质，但这些蛋白质只是在子细胞之间随机分配的免费汤吗？这可能是一些蛋白质的情况，但其他蛋白质需要与伴侣蛋白质以正确的比例分开才能发挥作用。这可以通过制造紧密、稳定的复合体来实现，但其他蛋白质组需要机制来确保每个子细胞都有正确比例的正确蛋白质。人们早就知道膜提供了一个框架，允许蛋白质聚集在一起，组织对外界变化做出反应的受体蛋白质，形成相互作用的蛋白质复合物。那么那些可溶的、对外界环境没有反应的蛋白质呢？它们是如何组织的？细胞又是如何确保子细胞继承正确数量的复合物的？最近人们意识到，在细菌细胞中，一些蛋白质复合物可以“搭在”复制和分离的染色体上，一种蛋白质松散地覆盖在染色体表面，并与一种蛋白质复合物相互作用。当染色体分离时，这种蛋白质携带这种大的蛋白质“货物”到子细胞。与染色体松散联系的蛋白质与已知的确保子细胞继承正确遗传物质的蛋白质有关，现在很清楚，细菌利用这个系统分离出各种蛋白质复合物，以正确的比例发挥正常功能。由于这是细菌间的共同系统，因此可以利用它来组织细菌间的其他蛋白质复合物。在许多代谢途径中，当蛋白质紧密结合确保局部高浓度和快速底物转移时，效率就会达到。如果这些途径在外来系统中表达，蛋白质通常是分散和无组织的，导致低效率的活性。此外，许多蛋白质与伴侣蛋白一起工作，为了了解它们是如何理想地工作的，需要在结合时对它们的结构进行表征，但通常这些蛋白质是单独纯化和混合的，或者单独表达时它们是不溶的。我们有可能利用这种自然系统分离蛋白质复合物，使其他蛋白质保持在功能复合物中，并保持高局部浓度。使用这种简化的系统，我们可以在合成生物学中使用该系统，允许子细胞以功能性但高比率的方式分离蛋白质，从而有效地产生所需的产品，或者它将允许在允许分离和结构分析的环境中表达蛋白质伴侣。为了能够利用这种新发现的机制，我们需要了解将蛋白质作为复合物结合在一起的基本成分，导致蛋白质复合物复制以及与染色体相关蛋白上的染色体的关联。

When a cell divides, in general it produces a reasonable replica of itself. As the cell grows it makes new proteins, so that, before division it is reasonable to assume it has twice as many proteins as the initial cell. When that cell divides each daughter needs a chromosome to make those proteins, but are the proteins just a free soup that gets randomly divided between the daughter cells? That may be the case for some proteins, but other proteins need to be divided with partner proteins in the right ratio to work. This can be done by making tight, stable complexes that get divided together, but other groups of proteins need mechanisms that ensure each daughter cell has the correct proteins in the correct ratio. Membranes have long been know to be provide a framework for allowing proteins to come together, organising receptor proteins that respond to changes in the external world into interacting protein complexes. What about proteins that are soluble and do not respond to the external environment-how to they organise and how do cells ensure daughter cells inherit the right number of complexes. It has recently been realised that in bacterial cells some protein complexes can "piggy-back" on the duplicated and segregating chromosomes, with a protein loosely covering the chromosome surface and also interacting with a complex of proteins. As the chromosome segregates this protein carries this large protein "cargo" to the daughter cell. The protein which loosely associates with the chromosome is related to proteins known to also ensure daughter cells inherit the right genetic material and it is now clear that bacteria use this system to segregate a wide range of protein complexes needed in the correct ratio to function properly. As this is a common system across bacteria, it could be harnessed to organise other protein complexes between bacteria. In many metabolic pathways efficient rates are achieved when proteins are closely associate ensuring local high concentrations and fast substrate transfer. If these pathways are expressed in alien systems the proteins are often diffuse and disorganised, resulting in inefficient rates of activity. In addition many proteins function with partner proteins and to understand how they work ideally their structures need to be characterised when bound, but usually the proteins are purified individually and mixed or when expressed individually they are insoluble. It is possible we can use this natural system for segregating protein complexes to keep other proteins in functional complexes and at high local concentrations. Using this reduced system we could either use the system in synthetic biology for allowing a daughter cells to segregate proteins in functional but high ratios for a pathway to efficiently produce a desired product or it will allow expression of protein partners in an environment that will allow their isolation and structural analysis. To be able to harness this newly identified mechanism we need to understand the essential components holding the proteins together as complexes, causing the protein complexes to duplicate and the association with the chromosome on the chromosome associated protein.