Ca²⁺ Regulates ERp57-Calnexin Complex Formation

Area of Science:

• Biochemistry
• Molecular Biology
• Cellular Biology

Background:

• ERp57 is a key disulfide catalyst in the endoplasmic reticulum (ER) involved in protein folding.
• ERp57 works with calnexin (CNX) and calreticulin (CRT) chaperones throughout protein folding.
• Maintaining protein homeostasis is vital for cellular function and disease prevention.

Purpose of the Study:

• To elucidate the regulatory mechanisms of calcium (Ca2+) on the ERp57-calnexin complex formation.
• To understand the functional roles of the ERp57-CNX complex in protein folding and aggregation.

Main Methods:

• Biochemical analyses were employed to study protein interactions.
• Isothermal titration calorimetry (ITC) was used to quantify binding thermodynamics.
• Functional assays assessed oxidative folding and client aggregation.

Main Results:

• ERp57 binds strongly to CNX via non-covalent interactions in the absence of Ca2+.
• The ERp57-CNX complex enhances oxidative folding of human leukocyte antigen heavy chains.
• The complex also effectively inhibits client protein aggregation.

Conclusions:

• Ca2+ plays a critical role in regulating the ERp57-calnexin interaction.
• The ERp57-CNX complex exhibits both enzymatic and chaperoning functions, particularly under Ca2+ depletion.
• These findings reveal molecular insights into the interplay between chaperone networks and Ca2+ in protein homeostasis.