Vesicles: membrane-bound organelle intermediates

The endomembrane system is perhaps the easiest way to identify a eukaryotic cell. It is composed of the various membranes that surround the organelles including the nuclear envelope, the endoplasmic reticulum (ER),  the Golgi bodies, the lysosomes (in animals), the vacuoles (in plants), endosomes and the plasma membrane.

This GIF, found on the Brooklyn Cuny Website, illustrates the pathways of proteins through the endomembrane system from the nuclear membrane (at the bottom-most part of the ER) to the lysosome or the plasma membrane. Proteins are stored in the lysosome or moved into the extracellular place. Note that transport vesicles link the larger organelles and carry proteins between them. 

Artemisa Garnica, a senior zoology major at CSU, explained that scientists study the endomembrane system to understand how and why proteins go to their respective locations. In this, we might be able to understand secretory diseases in both humans and animals, including some forms of cancer. 

Discovering Sec(retory) Mutants: The Genetics Behind Vesicles

On March 28, Randy Schekman, a 2013 Nobel Prize winner, gave a lecture in CSU's Lory Student Theater on "Genes and proteins that organize secretion and autophagy." Until the last 30 years, the mechanisms of the endomembrane transport system were largely unknown.

 Schekman and his lab were responsible for identifying secretory defects and looking for their genetic basis. One of the genes they related to a defect  became known as yeast cell gene Sec1 (labeled after its secretory mutation), according to Scheckman.  The Sec1 mutation disallowed membrane fusing between the vesicle and the plasma membrane so that the vesicles accumulated just inside the membrane.

His lab went on to identify several genes with secretory mutations, defects in vesicle budding, formation, and fusion.

In the lecture, he also explained that several human diseases occur due to secretory defects, including anemia and a rare condition that leads to incomplete formation of the skull.

The Mechanism
Schekman's lab also headed research on COPII, a coat protein that coats the vesicles.

According to Marinus Pilon, a Cell Biology professor at CSU who worked with Schekman, COP II is catalyzed to bind Sar during vesicle budding.

This image, found on the nature website shows vesicle budding, when a vesicle forms on the surface of the ER. The outer proteins (Sec23) bind to Sar  along with other proteins and form vesicles, which allow the stable transport of protein products through the cytoplasm.

These mechanisms provide possible points of investigation for diseases, especially if they result in the build-up of certain secreted proteins.