ER chaperone functions during normal and stress conditions

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Proteins destined for secretion or cellular compartments enter the endoplasmic reticulum (ER) unfolded.
• Inside the ER, proteins undergo folding, modification (e.g., N-linked glycosylation), and assembly, aided by chaperones and folding enzymes.
• ER stress disrupts protein folding, leading to unfolded protein accumulation and activating the unfolded protein response (UPR).

Purpose of the Study:

• To review the diverse roles of ER chaperones and folding enzymes.
• To discuss their functions under normal physiological conditions and during ER stress.
• To highlight their involvement in protein folding, quality control, and UPR signaling.

Main Methods:

• Literature review and synthesis of existing research on ER chaperones and the UPR.
• Analysis of the molecular mechanisms underlying protein folding and quality control in the ER.
• Examination of signaling pathways involved in the UPR.

Main Results:

• ER chaperones and folding enzymes are crucial for protein maturation in the ER.
• The UPR transcriptionally up-regulates ER chaperones and folding enzymes to combat ER stress.
• Some ER chaperones actively participate in UPR signaling, protein degradation, and UPR termination.
• ER chaperone levels can also increase during high-demand physiological states, like B cell differentiation.

Conclusions:

• ER chaperones and folding enzymes perform essential roles in protein homeostasis under both normal and stressed conditions.
• The UPR is a critical adaptive response that enhances the cell's capacity to manage unfolded proteins.
• Emerging evidence shows ER chaperones have multifaceted roles beyond protein folding, including signaling and degradation pathways.