Mechanisms of membrane pore formation

蛋白质的氨基酸序列由其遗传密码决定，决定了蛋白质的结构和功能。通常，天然（正确的）蛋白质结构是唯一的，并且是该特定蛋白质最稳定的形式。蛋白质在两种不同的环境中是稳定的：水溶性蛋白质存在于细胞和组织的溶液中，而膜蛋白存在于细胞膜的油状层中。可溶性蛋白比膜蛋白更容易处理，也更容易理解。尽管膜蛋白在许多关键的细胞功能中发挥着重要作用，如检测和响应来自环境的信号，细胞间的通信和营养物质的摄取，但与可溶性蛋白相比，膜蛋白的三维结构只有极少数是已知的。可溶性蛋白和膜蛋白的表面性质有很大的不同。一类非常有趣的蛋白质打破了一般的规则，即蛋白质要么是水溶性的，要么是插入膜中的。细菌毒素和免疫系统的某些蛋白质是作为单独的水溶性蛋白质合成的，但在它们发挥作用的过程中，它们聚集成环，穿透细胞膜，穿过目标膜穿孔。在细菌毒素的情况下，这种毒素的作用是为细菌释放营养物质，顺便杀死宿主细胞。在免疫系统中，当检测到感染细胞或癌细胞时，在免疫监视过程中会分泌成孔蛋白，以杀死它们。因此，形成孔隙的蛋白质已经进化成为生物体与其病原体之间“军备竞赛”的一部分。在这个项目中，我们正在研究细菌毒素溶肺素（肺炎和其他疾病的重要因素）和免疫系统蛋白穿孔素（对维持机体健康的免疫反应至关重要）形成的毛孔结构。孔与模型膜结合在一起，我们可以通过在电子显微镜下记录这些膜的快速冷冻悬浮液的图像来研究它们。通过适当的计算机图像处理，我们可以确定它们的三维结构，这将使我们了解这些蛋白质如何如此戏剧性地改变它们的形状和性质，以及膜是如何被刺穿的。

The amino acid sequence of a protein, determined by its genetic code, defines the structure and function of the protein. Usually, the native (correct) protein structure is unique, and is the most stable form for that particular protein. There are two distinct environments in which proteins are stable: water-soluble proteins are found in solution in cells and tissues, but membrane proteins are found in the oil-like layers of cellular membranes. Soluble proteins are much easier to work with and are much better understood than membrane proteins. Although membrane proteins play important roles in many key cellular functions such as detection and response to signals from the environment, communication between cells, and uptake of nutrients, only a tiny number of three-dimensional structures of membrane proteins are known in comparison to those of soluble proteins. The surface properties of soluble and membrane proteins are very different. A very interesting class of proteins break the general rule that proteins are either water-soluble or inserted into membranes. The bacterial toxins and certain proteins of the immune system are synthesised as individual, water-soluble proteins but in the course of their function, they assemble into rings that penetrate cell membranes and puncture holes through their target membranes. In the case of bacterial toxins, the role of such toxins is to release nutrients for the bacteria, incidentally killing the host cell. In the immune system, pore forming proteins are secreted in the course of immune surveillance when infected or cancerous cells are detected, in order to kill them. Thus, pore-forming proteins have evolved as part of the 'armaments race' between organisms and their pathogens. In this project, we are studying the structures of the pores formed by the bacterial toxin pneumolysin, an important factor in pneumonia and other diseases, and also by the immune system protein perforin, essential for the immune response to maintain the health of the organism. The pores are bound to model membranes, and we can study them by recording images of rapidly frozen suspensions of these membranes in an electron microscope. With suitable computer image processing we can determine their three-dimensional structures, which will give us an understanding of how these proteins change their shape and properties so dramatically, and how the membrane is punctured.