What about trafficking?

One other word that has frequently been mentioned in my blogs is 'trafficking'. Many people, even biologists might not understand what trafficking is or how it works. Thus, I think I will write another blog giving people some background of my research, in this case, trafficking.

Often, people would consider a negative connotation associated to the word 'trafficking'. For example, human trafficking, or drug trafficking. However in the scientific world, trafficking is not nearly as bad as its normal meaning. In fact, protein trafficking might have been an important feature that allows the development, and the evolution from prokaryotic to eukaryotic cells. There have been speculations that the protein trafficking systems would have to be evolved prior to the eukaryotic cells. Because simple cellular diffusion is often not sufficient as a method of substance transportation within eukaryotic cells, thus substance movements had to be archived via a specialized transport mechanism in eukaryotic cells rather than just diffusion.

Protein trafficking, or translocation involves rapid intracellular shuttlings of molecules packed in transportive vesicles. Cellular trafficking is often accomplished by following cellular tracks composed of cytoskeletonal proteins using motor proteins. In detail, some protein appeared to use different types of cytoskeleton tracks depending on the phase of the cell cycle. Translocation allows cells to store away unused proteins in vesicles, while rapidly mobilize and deploy them when a demand emerges. Though translocation, a cell greatly reduces its protein turn-over rates, which in turn, reduces the energy expenditure of a cell while performs all of its function at a timely fashion. It has been reported that the effects of translocation can be often seen within half an hour or less.

One of the important organelle used during trafficking is the Golgi apparatus. It plays two central roles in many cellular trafficking events; it is involved in protein synthesis and delivery, as well as internalizing molecular processes via endocytic. In more detail, brefeldin A, a chemical inhibits protein synthesis by blocking membrane trafficking from the endoplasmic reticulum to the Golgi apparatus proves that protein translocation is a necessary step in protein synthesis, as protein synthesis is often requires different organelles. In another study, it has also been found that besides protein synthesis, progression of murine oocyte maturation possibly also requires functional membrane trafficking.

Trafficking is a common phenomenon that has been observed across many species. For example, in humans, copper pumps are trafficked to the cell membrane from the E.R. in the presence of excessive cellular copper ions. Recently, trafficking has also been shown to be regulated by environmental cues. For example, in electric fishes, voltage-gated sodium channels are circadianly trafficked into the excitable membranes of electrogenic cells before conducting weak electric field for communication and navigation.

In conclusion, protein trafficking is not only a process that can greatly reduce the energy expenditure of a cell, while allowing all the cellular processes to run smoothly; it is also crucial in protein synthesis. Translocation might even be one of the features that allowed the evolution of higher organisms!