Structural Biochemistry/Chaperone Proteins

Chaperone Proteins in the Nucleolus

There are multiple chaperones and co-chaperones in the nucleolus. Chaperones are components of a larger network that promotes protein homeostasis. Studies show that cellular chaperones' network have individual compartments that have specific functions, which then even makes the cellular proteostatsis network more efficient. These unique network chaperones and multitasking proteins are present in the nucleoli, which supports and controls many important biological processes.

In eukaryote cells, many organelles have specific functions. The nucleus directs the largest number of necessary cellular processes. Within the nucleus, there is a nucleolus that is the most prominent compartment, contain a vast number of proteins, so it is therefore associated with many diseases and pathologies. The nucleoli functions due to a of a network or chaperones, co-chaperones, and multitasking proteins all work together to direct activities and adaptions due to stress.

Chaperone proteins helps the folding and unfolding of biological molecules. For example, RNA chaperones control RNA quality and play very important roles in ribosomes biogenesis. Chaperone proteins are also responsible in aging, cancer, protein folding, diabetes, and much much more. Chaperones need networks of co-chaperones and heat shock proteins for processes to work. Thus, their cooperation is organized into dynamic networks that promote effective interaction. Heat shock proteins HSP70s and HSP90s are critical in protein homeostasis to make sure polypeptides are functional and structured, protect cells from proteotoxicity. They bind to proteins. Each chaperone networks are separated by their distinct function.

The network of chaperones and multitasking proteins are in the nucleolus. Scientists have studied the HeLa cell nucleoli which helps them making some interesting conclusions. The abundance of chaperones and co-chaperones in nucleoli is regulated by the physiology of cells, but the quantitative data is unknown. Heat shock protein families were detected in the study by proteomics. Some of these proteins have multiple functions that contribute to many events and biological activities, known as nucleolus multitasking proteins (NoMPs). NoMPs can be in the nucleolus, nucleoplasm, and even the cytoplasm. Research with yeast proteins shows that nucleoli has a chaperone NoMP network committed just to have specific functions, which was tested with an assembly of possible networks that incorporated RNA chaperones, protein kinases, and phosphatases. Nucleolar chaperones NoMP network is made out of a unique set of protein factors, and it is dynamic to modulate nucleolar activities upon cell physiological changes.

There are many roles of chaperone networks. Roles of chaperone/NoMP network are specific to its clients, requiring coordination between co-factors and the designated group of chaperones. There are 4 types of proposed nucleolar networks. One of them is that chaperone networks are composed of multiple abilities that secures coordination of nucleolar processes. Another suggested network is centered around HSP90, its co-chaperones, and NoMps. HSP90 along with CDC37 inputs protein kinases for activation. In the nucleolus, HSP90 is associated with controlling CK2 activity, important for biological function. It's postulated that HSP90-CK2 regulates the activity of RNA polymerase I and ribosomes biogensis. Moreover, since CK2 is required to re-organize the nucleolus filaments due to changes in stress, the network is also responsible for proper nucleolar organization. A 3rd proposal is that chaperone HSPA8 also participates in the organization of the nucleoli by associating with fibrillarin. Protein chaperone networks are involved in a multitude of functions, including regulation of cell cycle, signaling events, and protein turnover.

Nucleolar chaperone / NoMP network promotes survival of the cell, because the processes they control are vital for growth conditions. The networks provide assistance to complete the tasks. Changes in stress or environment or viral infections can change the demand for chaperone or NoMP activities. Because of this, it's implied that nucleoli are at the center of essential cellular activities. NoMP network offer unique opportunities for therapeutic intervention.