Tag: Proteostasis

Protein misfolding occurs when proteins fail to achieve or maintain their correct three-dimensional structures. Explore its causes, cellular consequences, quality-control mechanisms, and connection to disease.

Protein homeostasis is the process by which cells maintain a balance between protein synthesis and degradation. This balance is essential for protein quality, cellular function, growth, adaptation, and survival.

ERAD is a central ER quality‑control pathway that recognises misfolded proteins, retrotranslocates them to the cytosol, ubiquitinates them and directs them to the proteasome. By preventing proteotoxic accumulation, ERAD preserves ER homeostasis and supports cellular proteostasis.

PERK is a central ER stress sensor that phosphorylates eIF2α, reduces protein synthesis and activates ATF4‑dependent transcription. Through adaptive and apoptotic signalling, PERK coordinates unfolded protein response pathways that restore proteostasis or eliminate irreparably damaged cells.

IRE1 is the most conserved ER stress sensor, activating XBP1 splicing and RIDD to restore proteostasis. Through its kinase and RNase activities, IRE1 detects misfolded proteins, initiates adaptive signalling and coordinates the unfolded protein response during ER stress.

The proteostasis network is an integrated system of chaperones, degradation pathways and organelle‑specific quality‑control mechanisms that maintains protein folding, stability and function. By coordinating refolding, repair and degradation, cells prevent proteotoxic stress and preserve homeostasis.

The unfolded protein response (UPR) is a conserved ER stress pathway that detects misfolded proteins and restores proteostasis. Through IRE1, PERK and ATF6 signalling, cells expand folding capacity, reduce protein load and maintain homeostasis under conditions of ER stress.

The heat‑shock response (HSR) is a conserved cellular defence pathway that protects the proteome under stress. By activating HSF1 and inducing heat‑shock proteins, cells stabilise protein folding, prevent aggregation and restore proteostasis during proteotoxic conditions.

Cellular stress responses are adaptive defence mechanisms that protect cells from environmental, metabolic and proteotoxic stress. By activating heat‑shock proteins, unfolded protein responses, antioxidant pathways and autophagy, cells restore homeostasis and maintain functional integrity under adverse conditions.

Protein quality control (PQC) is a cellular surveillance system that preserves proteome integrity by monitoring protein folding, repairing misfolded proteins and eliminating damaged or aggregated species. Through coordinated action of chaperones, the ubiquitin–proteasome system and autophagy, PQC protects cells from proteotoxic stress and maintains homeostasis.

U‑box ubiquitin ligases are RING‑type E3 enzymes with a modified U‑box domain that enables zinc‑independent ubiquitin transfer. Key members such as CHIP, PRPF19 and UBOX5 regulate chaperone‑mediated protein quality control, DNA‑damage repair and cellular stress responses, making the U‑box family essential for proteostasis and genome stability.

HECT ubiquitin ligases are catalytic E3 enzymes that form a thioester intermediate with ubiquitin, allowing precise control of ubiquitin‑chain architecture. Through NEDD4‑family ligases, HERC proteins and HUWE1, the HECT class regulates receptor endocytosis, DNA‑damage signalling, proteostasis and diverse cellular stress responses.

K48‑linked ubiquitination is the principal degradation signal in eukaryotic cells, directing proteins to the 26S proteasome. Built by E1, E2 and E3 enzymes, K48‑linked chains regulate protein turnover, cell‑cycle progression and DNA‑damage responses, forming a central mechanism for maintaining proteostasis and preventing toxic protein accumulation.

Protein folding is the process by which newly synthesized proteins acquire their functional three-dimensional structures. Discover how folding occurs, what influences it, and how cells manage misfolded proteins.

Cellular homeostasis is the dynamic process that maintains internal stability by regulating ions, metabolism, proteostasis, organelle function and genomic integrity. Through coordinated signalling networks and adaptive stress responses, cells preserve equilibrium and protect themselves from dysfunction and disease.