by PhilipJ on 6 June 2009
Our cells are filled with compartments, each performing a specific function. Some of these compartments, such as mitochondria and lysozomes, are very large and enclose many different molecular machines. Other intracellular compartments are smaller, such as the transport vesicles that shuttle proteins from site to site inside the cell. Most of these compartments, including mitochondria, lysozomes and transport vesicles, are surrounded by membranes. However, in special cases, cells build smaller compartments surrounded by a protein shell. In our own cells, vaults are a spectacular example of these protein-enclosed compartments.
Vaults are composed of many copies of the major vault protein, which assembles to form a hollow football-shaped shell. The one shown here is from rat liver cells (PDB entries 2zuo, 2zv4, and 2zv5) and contains 78 copies of the protein. Inside cells, the vault also encloses a few other molecules, which were not seen in the crystal structure because they don’t have a symmetrical structure inside the vault. These molecules include several small RNA molecules, a protein that binds to RNA, and an enzyme that adds nucleotides to proteins.
Read more by David Goodsell at the RCSB PDB here.