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Evidence for a novel ATP-dependent protease from the rat liver mitochondrial intermembrane space: purification and
N Sitte1, W Dubiel, P M Kloetzel
1Institute of Biochemistry, Medical Faculty (Charité), Humboldt University Berlin, Hessische Str. 3-4, D-10115 Berlin, Germany. nsitte@rz.charite.hu-berlin.de
Abstract:
An ATP-dependent protease in the intermembrane space of rat liver mitochondria, MISP I (mitochondrial intermembrane space protease), was partially purified and characterised. The protease complex has a molecular mass of 200 kDa and appears to be an oligomeric enzyme complex. The proteolytic activity of the enzyme can be stimulated up to 3-fold by Mg2+ATP. The Km for ATP is 200 microM. Nucleoside triphosphates, but not ADP, AMP, or nonhydrolysable ATP analogues, can substitute for ATP. The protease exhibits multicatalytic properties with chymotrypsin-like, peptidyl-glutamyl-hydrolysing, and trypsin-like activities. Of the latter the trypsin-like activity is not enhanced by ATP. In addition to the hydrolysis of fluorogenic peptide substrates the protease is able to degrade radiolabeled model proteins. The ATP-dependent mitochondrial protease was characterised as a cysteine protease sensitive to hemine. The cross reactivity of an anti-human-S4 antibody raised against an ATPase subunit of the PA700 complex with a component of MISP I indicated a structural relationship. Furthermore, ATP-agarose-binding assays revealed the connection of the peptide hydrolysing activity with an ATP binding domain. The data presented here and a comparison with known ATP-dependent mitochondrial proteases demonstrated that MISP I represents a novel ATP-dependent protease in the mitochondrial intermembrane space of rat liver.
Insights
Researchers identified a novel ATP-dependent protease, MISP I, in rat liver mitochondria. This mitochondrial intermembrane space protease exhibits multicatalytic activity and is structurally related to known ATPases.
Area of Science:
- Mitochondrial biology
- Protease biochemistry
- Cellular respiration
Background:
- Mitochondria possess an intermembrane space containing various enzymes.
- ATP-dependent proteases play crucial roles in protein degradation and cellular homeostasis.
- Understanding mitochondrial proteases is key to deciphering cellular quality control mechanisms.
Purpose of the Study:
- To partially purify and characterize a novel ATP-dependent protease from rat liver mitochondria.
- To investigate the enzymatic properties and substrate specificity of the identified protease.
- To determine the structural and functional relationship of this protease with known protein degradation systems.
Main Methods:
- Partial purification of the mitochondrial intermembrane space protease (MISP I).
- Enzymatic assays using fluorogenic peptide substrates and radiolabeled model proteins.
- Biochemical characterization including molecular mass determination, ATP dependency, and substrate analysis.
- Immunological cross-reactivity studies and ATP-agarose binding assays.
Main Results:
- A 200 kDa ATP-dependent protease complex, MISP I, was identified in the mitochondrial intermembrane space.
- MISP I exhibits multicatalytic activity (chymotrypsin-like, peptidyl-glutamyl-hydrolysing, trypsin-like) and is stimulated by Mg2+ATP.
- The protease is a cysteine protease sensitive to hemine and shows structural similarity to components of the PA700 complex, indicating an ATP-binding domain.
- MISP I degrades model proteins, suggesting a role in mitochondrial protein quality control.
Conclusions:
- MISP I represents a novel ATP-dependent protease located in the mitochondrial intermembrane space of rat liver.
- Its multicatalytic nature and ATP dependency suggest a significant role in mitochondrial protein turnover.
- The structural relationship to known ATPases highlights conserved mechanisms in ATP-dependent proteolysis within mitochondria.