Thinking about p24 proteins and how transport vesicles select their cargo

All cells are divided into distinct subcellular compartments, each with its own defining set of proteins. A fundamental problem in molecular cell biology is to understand how proteins that are synthesized on ribosomes in the cytoplasm reach their proper intracellular address. This process, usually called protein sorting or protein trafficking, is understood to involve information encoded in the protein sequence itself as well as the cellular machinery that decodes this information and delivers the protein to its correct location. Many of the sorting steps in a eukaryotic cell take place along the secretory pathway. At each step in the secretory pathway, carrier vesicles bud from one compartment and then fuse with the membrane of the next compartment allowing the transfer of membranes and proteins between organelles. To sort proteins, transport vesicles must be able to select the appropriate contents, accepting cargo proteins that should advance to the next compartment while excluding compartmental resident proteins that should remain in place. The companion article for this commentary concerns the function of the p24 family of vesicle proteins, which are thought to play an important part in cargo selection (1).