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Molecular cloning and characterization of MT-ACT48, a novel mitochondrial acyl-CoA thioesterase
1CJF 97-10 INSERM, Faculté Necker-Enfants Malades, 156 rue de Vaugirard, 75756 Paris Cedex 15, France.
Abstract:
While characterizing Eps15 partners, we identified a 48-kDa polypeptide (p48) which was precipitated by Eps15-derived glutathione S-transferase fusion proteins. A search in a murine expressed sequence tag data base with N-terminal microsequences of p48 led to the identification of two complete cDNA clones encoding two isoforms of a 439-amino acid protein sharing 95% nucleic and amino acid identity. Northern blot and immunoblotting studies showed that p48 was ubiquitously expressed. A significant homology (19% identity and 40% similarity) between p48 and rat brain cytosolic acyl-CoA thioesterase was observed in an 80-amino acid C-terminal domain, retrieved from proteins from human, nematode, and plants. The thioesterase function of p48 was further demonstrated against long chain acyl-CoAs in a spectrophotometric assay. Furthermore, data obtained from sequence analysis showed that p48 contained a mitochondrial targeting signal, cleaved in mature protein as assessed by microsequencing. The mitochondrial localization of both endogenous and transfected p48 was confirmed by confocal microscopy. These results indicate that p48, called MT-ACT48 (mitochondrial acyl-CoA thioesterase of 48 kDa), defines a novel family of mitochondrial long chain acyl-CoA thioesterases.
Insights
Researchers identified a novel mitochondrial protein, p48 (MT-ACT48), which functions as a long-chain acyl-CoA thioesterase. This discovery defines a new family of mitochondrial enzymes involved in fatty acid metabolism.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Biology
Background:
- Eps15 is a known protein involved in cellular processes.
- Characterization of Eps15 partners can reveal novel cellular functions and proteins.
Purpose of the Study:
- To identify and characterize novel binding partners of Eps15.
- To determine the function and localization of a newly identified protein, p48.
Main Methods:
- Glutathione S-transferase (GST) pull-down assays to identify Eps15 binding partners.
- Database searching using N-terminal microsequences.
- Northern blot and immunoblotting for expression analysis.
- Spectrophotometric assays to determine enzyme activity.
- Sequence analysis for identifying functional domains (e.g., mitochondrial targeting signal).
- Confocal microscopy for subcellular localization studies.
Main Results:
- A 48-kDa polypeptide (p48) was identified as an Eps15 binding partner.
- cDNA cloning revealed two isoforms of p48, sharing high sequence identity.
- p48 is ubiquitously expressed.
- p48 exhibits homology to acyl-CoA thioesterases and possesses thioesterase activity against long-chain acyl-CoAs.
- Sequence analysis indicated a mitochondrial targeting signal, and confocal microscopy confirmed mitochondrial localization.
- p48 was named MT-ACT48 (mitochondrial acyl-CoA thioesterase of 48 kDa).
Conclusions:
- p48, now designated MT-ACT48, is a novel mitochondrial enzyme.
- MT-ACT48 represents a new family of mitochondrial long-chain acyl-CoA thioesterases.
- This finding expands our understanding of mitochondrial fatty acid metabolism and enzyme families.