Article

Degradation of the amyloid β-protein by the novel mitochondrial peptidasome, PreP

Department of Biochemistry and Biophysics , Stockholm University, Tukholma, Stockholm, Sweden
Journal of Biological Chemistry (Impact Factor: 4.57). 10/2006; 281(39):29096-104. DOI: 10.1074/jbc.M602532200
Source: PubMed

ABSTRACT Recently we have identified the novel mitochondrial peptidase responsible for degrading presequences and other short unstructured peptides in mitochondria, the presequence peptidase, which we named PreP peptidasome. In the present study we have identified and characterized the human PreP homologue, hPreP, in brain mitochondria, and we show its capacity to degrade the amyloid beta-protein (Abeta). PreP belongs to the pitrilysin oligopeptidase family M16C containing an inverted zinc-binding motif. We show that hPreP is localized to the mitochondrial matrix. In situ immuno-inactivation studies in human brain mitochondria using anti-hPreP antibodies showed complete inhibition of proteolytic activity against Abeta. We have cloned, overexpressed, and purified recombinant hPreP and its mutant with catalytic base Glu(78) in the inverted zinc-binding motif replaced by Gln. In vitro studies using recombinant hPreP and liquid chromatography nanospray tandem mass spectrometry revealed novel cleavage specificities against Abeta-(1-42), Abeta-(1-40), and Abeta Arctic, a protein that causes increased protofibril formation an early onset familial variant of Alzheimer disease. In contrast to insulin degrading enzyme, which is a functional analogue of hPreP, hPreP does not degrade insulin but does degrade insulin B-chain. Molecular modeling of hPreP based on the crystal structure at 2.1 A resolution of AtPreP allowed us to identify Cys(90) and Cys(527) that form disulfide bridges under oxidized conditions and might be involved in redox regulation of the enzyme. Degradation of the mitochondrial Abeta by hPreP may potentially be of importance in the pathology of Alzheimer disease.

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    • "By virtue of their distinctive subcellular localizations and pH optima, AβDPs constitute powerful tools for manipulating different pools of Aβ and, thereby, gaining fresh insight into their potential involvement in the pathogenesis of AD (Leissring and Turner, 2013). AβDPs are present in a diverse range of subcellular compartments: insulin-degrading enzyme (IDE) in cytosol (Roth, 2004), IDE and presequence peptidase in mitochondria (Leissring et al., 2004; Falkevall et al., 2006), BACE-2 and endothelin-converting enzymes 1-and -2 in endosomes (Eckman et al., 2001; Abdul- Hay et al., 2012), and in cathepsins B and D in lysosomes (Gan et al., 2004; Leissring et al., 2009) (see Saido and Leissring, 2012; Leissring and Turner, 2013 for comprehensive reviews). Collectively, these AβDPs represent a diverse set of experimental tools for selectively manipulating different pools of Aβ. "
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    • "Therefore the free targeting peptides have to be degraded or removed from the organelles. This is achieved by the targeting peptide degrading peptidasome, called Presequence Protease, PreP [31] [32] [33]. "
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    ABSTRACT: Most of the mitochondrial and chloroplastic proteins are nuclear encoded and synthesized in the cytosol as precursor proteins with N-terminal extensions called targeting peptides. Targeting peptides function as organellar import signals, they are recognized by the import receptors and route precursors through the protein translocons across the organellar membranes. After the fulfilled function, targeting peptides are proteolytically cleaved off inside the organelles by different processing peptidases. The processing of mitochondrial precursors is catalyzed in the matrix by the Mitochondrial Processing Peptidase, MPP, the Mitochondrial Intermediate Peptidase, MIP (recently called Octapeptidyl aminopeptidase 1, Oct1) and the Intermediate cleaving peptidase of 55kDa, Icp55. Furthermore, different inner membrane peptidases (Inner Membrane Proteases, IMPs, Atp23, rhomboids and AAA proteases) catalyze additional processing functions, resulting in intra-mitochondrial sorting of proteins, the targeting to the intermembrane space or in the assembly of proteins into inner membrane complexes. Chloroplast targeting peptides are cleaved off in the stroma by the Stromal Processing Peptidase, SPP. If the protein is further translocated to the thylakoid lumen, an additional thylakoid-transfer sequence is removed by the Thylakoidal Processing Peptidase, TPP. Proper function of the D1 protein of Photosystem II reaction center requires its C-terminal processing by Carboxy-terminal processing protease, CtpA. Both in mitochondria and in chloroplasts, the cleaved targeting peptides are finally degraded by the Presequence Protease, PreP. The organellar proteases involved in precursor processing and targeting peptide degradation constitute themselves a quality control system ensuring the correct maturation and localization of proteins as well as assembly of protein complexes, contributing to sustenance of organelle functions. Dysfunctions of several mitochondrial processing proteases have been shown to be associated with human diseases. This article is part of a Special Issue entitled: Protein Import and Quality Control in Mitochondria and Plastids.
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    • "Unexpectedly, studies on human brain mitochondria have demonstrated that PreP is the main peptidase degrading the amyloid b (Ab) peptide associated with Alzheimer's disease (AD) (Falkevall et al, 2006). AD is a progressive neurodegenerative disorder characterized by the accumulation of intracellular neurofibrillary tangles and extracellular plaques of Ab peptides in the brain. "
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