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The unfolded protein response (UPR) is a cellular stress response related to the endoplasmic reticulum (ER) stress. [1] It has been found to be conserved between mammalian species, [2] as well as yeast [1] [3] and worm organisms. The UPR is activated in response to an accumulation of unfolded or misfolded proteins in the lumen of the
Therefore, the proteasome pathway may not be efficient enough to degrade the misfolded proteins prior to aggregation. Misfolded proteins can interact with one another and form structured aggregates and gain toxicity through intermolecular interactions. [42]
Misfolded proteins can form protein aggregates or amyloid fibrils, get degraded, or refold back to its native structure. In molecular biology , protein aggregation is a phenomenon in which intrinsically-disordered or mis-folded proteins aggregate (i.e., accumulate and clump together) either intra- or extracellularly.
In cultured cells, when the production of misfolded proteins exceeds the capacity of the chaperone refolding system and the ubiquitin-proteasome degradation pathway, misfolded proteins are actively transported to a cytoplasmic juxtanuclear structure called an aggresome.
Endoplasmic-reticulum-associated protein degradation is one of several protein degradation pathways in the ER. Endoplasmic-reticulum-associated protein degradation (ERAD) designates a cellular pathway which targets misfolded proteins of the endoplasmic reticulum for ubiquitination and subsequent degradation by a protein-degrading complex, called the proteasome.
Cellular stress response pathways detect and alleviate proteotoxic stress which is triggered by imbalances in proteostasis. The cell-autonomous regulation occurs through direct detection of misfolded proteins or inhibition of pathway activation by sequestering activating components in response to heat shock.
The mitochondrial unfolded protein response (UPR mt) is a cellular stress response related to the mitochondria. The UPR mt results from unfolded or misfolded proteins in mitochondria beyond the capacity of chaperone proteins to handle them. [1] The UPR mt can occur either in the mitochondrial matrix or in the mitochondrial inner membrane. [1]
To maintain cellular homeostasis, the cellular quality control system must distinguish between folded and misfolded proteins. A misfolded protein will be recognized and tightly taken care of by either refolding or ubiquitination and proteasomal degradation. However, cellular increase of misfolded protein loads, due to various kinds of stresses ...