Immunoaffinity purification of the calpains

Area of Science:

• Biochemistry
• Molecular Biology
• Protein Purification

Background:

• Calpains are calcium-dependent cysteine proteases involved in various cellular processes.
• Mu-calpain and m-calpain are distinct isoforms with different cellular roles.
• Efficient purification of active calpains is crucial for biochemical and functional studies.

Purpose of the Study:

• To develop and validate an immunoaffinity chromatography method for purifying active mu- and m-calpains.
• To assess the purity and activity of calpains obtained using this method.
• To identify the epitope recognized by the monoclonal antibody.

Main Methods:

• Immunoaffinity chromatography utilizing a monoclonal antibody against the 28-kDa subunit common to mu- and m-calpains.
• Pre-purification of crude extracts using phenyl Sepharose and ion-exchange chromatography.
• Elution of bound calpains under conditions that preserve proteolytic activity.

Main Results:

• The immunoaffinity column successfully purified both mu- and m-calpains in a proteolytically active form.
• Single-pass purification yielded >90% purity for m-calpain and >70% purity for mu-calpain.
• The antibody epitope is located between amino acids 92 and 104 of the 28-kDa subunit, suggesting potential conformational shielding in the native molecule.

Conclusions:

• Immunoaffinity chromatography with the described monoclonal antibody is an effective strategy for purifying active mu- and m-calpains.
• The method offers high efficiency, particularly for m-calpain purification.
• Understanding epitope accessibility provides insights into calpain structure and antibody binding.