Function and structure of recombinant single chain calcineurin

Area of Science:

• Biochemistry
• Molecular Biology
• Enzymology

Background:

• Calcineurin (CN) is a crucial Ca(2+)/calmodulin-dependent serine/threonine protein phosphatase involved in T-cell activation and other signaling pathways.
• Native CN is a heterodimer of catalytic (CNA) and regulatory (CNB) subunits, with structural insights revealing subunit proximity and distinct functional domains.

Purpose of the Study:

• To construct and characterize a single-chain recombinant calcineurin by fusing its CNA and CNB subunits.
• To determine if subunit fusion affects the enzyme's folding, structure, biochemical properties, and functionality.

Main Methods:

• Amplification of a fused CNA-CNB gene using linker primers with glycine codons.
• Purification of the single-chain calcineurin and assessment of its solubility and specific activity.
• Biochemical and kinetic analyses, including Ca(2+)/calmodulin activation and divalent metal ion stimulation (Mn(2+), Ni(2+)).
• Structural conformation analysis using intrinsic fluorescence spectroscopy and circular dichroism spectropolarimetry.

Main Results:

• A soluble, highly active single-chain calcineurin was successfully constructed and purified.
• The recombinant enzyme exhibited biochemical properties and kinetic parameters comparable to native bovine brain calcineurin.
• The fused calcineurin retained Ca(2+)/calmodulin activation, divalent metal ion stimulation, and showed identical solution conformations to the native enzyme.
• The fusion did not impede correct subunit binding or affect folding pathways and structural changes crucial for function.

Conclusions:

• Fusion of calcineurin's catalytic and regulatory subunits yields a stable, functional enzyme.
• The single-chain structure preserves the native enzyme's biochemical and structural integrity.
• This recombinant calcineurin is a valuable tool for investigating intracellular signaling pathways and T-cell activation.