Removing coordinated metal ions from proteins: a fast and mild method in aqueous solution

Area of Science:

• Biochemistry
• Protein Chemistry
• Analytical Chemistry

Background:

• Metal-free proteins are crucial for thermodynamic and kinetic studies but are challenging to isolate.
• Existing methods for metal ion removal from proteins are often inefficient or harsh, potentially damaging protein structure and function.

Purpose of the Study:

• To develop a rapid, mild, and generalizable method for obtaining metal-free proteins.
• To validate the efficacy of the developed method using Ca-ATPase, a protein with high calcium affinity.

Main Methods:

• Utilized column chromatography with a commercially available Ni-NTA stationary phase, with Ni2+ ions removed.
• Employed the Ni2+-free NTA gel as a cation chelator to bind and remove metal ions from protein solutions.
• Tested the method on Ca-ATPase, an integral membrane protein.

Main Results:

• Achieved a 95% reduction in total Ca2+ ions from Ca-ATPase, yielding an essentially metal-free protein.
• Demonstrated the method's efficiency using a small amount of NTA gel.
• Confirmed that the protein retained its enzymatic activity after the metal ion removal process.

Conclusions:

• The Ni2+-free NTA chromatography is a highly effective and mild technique for preparing metal-free proteins.
• This method is broadly applicable for the removal of various metal ions from proteins.
• The preservation of enzymatic activity highlights the method's suitability for functional and structural protein research.