Prion protein - mediator of toxicity in multiple proteinopathies

Amyloid fibrils are aggregates of misfolded proteins.  Under most circumstances, misfolded proteins are either refolded by chaperone proteins or degraded by the proteasome. However, in the case of a mutation or a disease, these proteins can accumulate to form large clusters and often further assemble to form elongated fibers, called fibrils. 
Amyloid deposits were observed as early as 1639 in the liver and the spleen.   In 1854, Rudolph Virchow performed iodine staining,...

Eukaryotic cells can degrade proteins through several pathways. One of the most important among these is the ubiquitin-proteasome pathway. It helps the cell eliminate the misfolded, damaged, or unwarranted cytoplasmic proteins in a highly specific manner.
In this pathway, the target proteins are first tagged with small proteins called ubiquitin. This involves participation of a series of enzymes including— E1 (ubiquitin-activating enzyme), E2 (ubiquitin-conjugating enzyme), and E3...

Eukaryotic cells can degrade proteins through several pathways. One of the most important amongst these is the ubiquitin-proteasome pathway. It helps the cell eliminate the misfolded, damaged, or unwarranted cytoplasmic proteins in a highly specific manner.
In this pathway, the target proteins are first tagged with small proteins called ubiquitin. A series of enzymes carry out the ubiquitination of the target proteins - E1 (ubiquitin-activating enzyme), E2 (ubiquitin-conjugating enzyme), and E3...

Proteins are broken down into amino acids during digestion. Unlike fats and carbohydrates, which are stored for later use, proteins are not. Instead, amino acids are either used to produce ATP through oxidation or contribute to the creation of new proteins for the growth and repair of the body. Any surplus amino acids from the diet are converted into glucose or triglycerides rather than excreted.
Amino acids play various roles in the body once they are absorbed into cells. They are restructured...

The ER is the hub of protein synthesis in a cell. It has robust systems to quality control protein folding and also for degradation of terminally misfolded proteins. Under normal conditions, a small proportion of misfolded proteins that cannot be salvaged need to be transported to the cytoplasm by the ER-associated degradation or ERAD pathways. However, if the ERAD cannot handle the misfolded proteins, the cell activates the unfolded protein response or UPR to adjust the protein folding...