Every one of the trillions of cells in the human body are surrounded by a membrane that contains an enormous variety of transmembrane proteins. These proteins mediate the interactions of a cell with the outside world including other cells, the blood and the immune system. Transmembrane proteins also permit small molecules, nutrients and as well as many pathogens to selectively traverse the otherwise impermeable membrane barriers. Hence the protein composition of a cell’s outer membrane must be carefully and dynamically regulated if cells are to survive i.e the right amounts of the right proteins must be in the right membrane at the right time. Cells achieve this control by moving the transmembrane proteins to compartments inside the cell in small transport vesicles formed by ‘pinching off’ a small portion of the parent membrane. That these transport processes are fundamental is reflected by the fact that ~30% of mammalian proteins are either components of this transport machinery or its cargo.

All transport vesicles are built in a similar way as they need to carry out the same functions – hence they can be considered as the ‘white vans’ of the cell: they look similar and go everywhere, delivering all manner of cargo. The focus of this talk will be on the architecture and function of these ‘white vans’, which is of fundamental biological as well as medical importance. I hope to show you that, by visualising these structures at atomic resolution, which we have done using data collected at the Diamond Light Source near Didcot, we are now able to understand how fundamental processes inside the cell work.