Defining factors that ensure unidirectionality of endocytosis

点击翻译按钮获取中文摘要

Cells are the basic unit of life and all organisms are composed of one or more cells. These cells are covered in proteins that are embedded in their cell surface. This protein coat helps cells to perform certain functions such as responding to chemical messages. The coat also lets other cells recognise it. An analogy would be recognising groups of people according to the clothes they wear. However, sometimes a message that a cell receives tells it to behave differently. It therefore needs to remove elements of its protein coat. One of the ways that many cells do this is by a process of internalising some of the proteins from the coat. This protein internalisation is achieved by a process called endocytosis. The surface of the cell folds inwards in small portions and then pinches off inside the cell. This forms a small vesicle that can then carry the protein away inside the cell. Often the proteins get broken down and their most basic parts are released for re-use by the cell. In this way the parts of the coat that are not needed can be removed. At the same time, this process is often balanced by the addition of new proteins, which respond to different messages, to the cell surface. If the proteins are not removed properly because endocytosis is not functioning correctly, the cell could have proteins at the surface that send conflicting messages that may be detrimental to the well-being of the cell. Several diseases have been associated with defective endocytosis including Alzheimers, Huntingtons and cancer. In addition, several pathogens and toxins exploit the endocytic pathway to gain entry to cells. This project aims to use a simple system to understand how cells can take-up proteins from their surface. We are using a model organism called yeast because the molecules involved in the endocytic process are very similar to those in more complex human cells, but the yeast cells are much easier to manipulate to investigate the processes we are interested in. In particular we are trying to determine the mechanisms that ensure that once the internalisation process has begun, that it continues to completion. We know that the endocytosis process involves more than 50 proteins. Many of them form groups or complexes with one another, and then components of these groups interact with a single factor that is called Las17/WASP. We aim to test the idea that this particular protein acts as a ratchet in the endocytic process. By closely regulating the interactions of this one protein, the cell can ensure that interactions take place sequentially. Overall, we think that this might be the mechanism that ensures key stages of endocytosis proceed in a linear fashion rather than starting and then reversing or aborting before the invagination has completed and the membrane has pinched off inside the cell. We will use a wide range of techniques both inside and outside of the cell environment to investigate the interactions of Las17/WASP and to determine how these interactions are regulated to ensure endocytosis functions correctly.