Structural characterization of the human DjC20/HscB cochaperone in solution

Area of Science:

• Molecular Biology
• Biochemistry
• Structural Biology

Background:

• J-domain proteins (JDPs) are essential molecular chaperones regulating proteostasis.
• Human DjC20 (HscB) is a type III JDP crucial for mitochondrial [FeS] protein biogenesis, assisting HSPA9.
• The N-terminal zinc-finger domain of human DjC20 is critical for its function.

Purpose of the Study:

• To investigate the solution structure of human DjC20 (hDjC20).
• To determine the role of zinc ions (Zn²⁺) in hDjC20 stability and function.

Main Methods:

• Recombinant protein expression and purification.
• Small-angle X-ray scattering (SAXS) and SEC-MALS for structural analysis.
• Thermal and chemical denaturation assays in the presence of chelating agents (EDTA, DTPA).

Main Results:

• Recombinant hDjC20 was pure, folded, and stimulated HSPA9 ATPase activity.
• SAXS and SEC-MALS indicated hDjC20 exists as a slightly elongated monomer.
• Zn²⁺ was present at a 1:1 stoichiometry and resistant to removal by EDTA/DTPA.
• EDTA-induced denaturation revealed reduced protein stability, highlighting Zn²⁺'s role.

Conclusions:

• Zinc ions bind with high affinity to hDjC20, playing a vital role in its structural integrity.
• The stability conferred by Zn²⁺ is essential for hDjC20's chaperone function.
• Understanding hDjC20-Zn²⁺ interactions provides insights into JDP mechanisms.