Purification and characterization of a processing protease from rat liver mitochondria

Area of Science:

• Mitochondrial Biology
• Protease Biochemistry
• Enzymology

Background:

• Mitochondria import precursor proteins synthesized in the cytoplasm.
• Mitochondrial processing proteases are essential for maturation and targeting of these proteins.
• Characterization of these proteases is key to understanding mitochondrial biogenesis.

Purpose of the Study:

• To purify and characterize a novel processing protease from rat liver mitochondria.
• To elucidate the subunit composition and enzymatic properties of the purified protease.
• To investigate the substrate specificity and catalytic mechanism of the protease.

Main Methods:

• Purification of protease from rat liver mitochondrial matrix fraction.
• SDS-PAGE and gel filtration for subunit and molecular weight determination.
• Enzymatic assays using mitochondrial protein precursors (adrenodoxin, malate dehydrogenase, P-450s) and analysis of cleavage products.
• Inhibition studies with metal chelators and reactivation with divalent cations.

Main Results:

• A processing protease was purified, consisting of two subunits (55 kd and 52 kd) forming a 105 kd heterodimeric complex.
• The protease cleaved multiple mitochondrial protein precursors, including adrenodoxin, malate dehydrogenase, and P-450 variants, with varying efficiencies.
• Endoproteolytic cleavage was confirmed using adrenodoxin precursor.
• Protease activity was inhibited by metal chelators and restored by Mn2+, identifying it as a metalloprotease.

Conclusions:

• A novel heterodimeric metalloprotease involved in mitochondrial protein processing has been identified and purified.
• This protease plays a role in the maturation of various mitochondrial proteins destined for different compartments.
• The enzyme's metalloprotease activity, dependent on divalent cations like Mn2+, is crucial for its function.