Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.4.21.64 (proteinase K)
 4,071 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Transmissible spongiform encephalopathy diseases are characterized by conversion of the normal protease-sensitive host prion protein, PrP-sen, to an abnormal protease-resistant form, PrP-res. In the current study, deletions were introduced into the flexible tail of PrP-sen (23) to determine if this region was required for formation of PrP-res in a cell-free assay. PrP-res formation was significantly reduced by deletion of residues 34-94 relative to full-length hamster PrP. Deletion of another nineteen amino acids to residue 113 further reduced the amount of PrP-res formed. Furthermore, the presence of additional proteinase K cleavage sites indicated that deletion to residue 113 generated a protease-resistant product with an altered conformation. Conversion of PrP deletion mutants was also affected by post-translational modifications to PrP-sen. Conversion of unglycosylated PrP-sen appeared to alter both the amount and the conformation of protease-resistant PrP-res produced from N-terminally truncated PrP-sen. The N-terminal region also affected the ability of hamster PrP to block mouse PrP-res formation in scrapie-infected mouse neuroblastoma cells. Thus, regions within the flexible N-terminal tail of PrP influenced interactions required for both generating and disrupting PrP-res formation.
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PMID:N-terminal truncation of prion protein affects both formation and conformation of abnormal protease-resistant prion protein generated in vitro. 1146 11

A fundamental event in the pathogenesis of transmissible spongiform encephalopathies (TSE) is the conversion of a normal, proteinase K-sensitive, host-encoded protein, PrP-sen, into its protease-resistant isoform, PrP-res. During the formation of PrP-res, PrP-sen undergoes conformational changes that involve an increase of beta-sheet secondary structure. While previous studies in which PrP-sen deletion mutants were expressed in transgenic mice or scrapie-infected cell cultures have identified regions in PrP-sen that are important in the formation of PrP-res, the exact role of PrP-sen secondary structures in the conformational transition of PrP-sen to PrP-res has not yet been defined. We constructed PrP-sen mutants with deletions of the first beta-strand, the second beta-strand, or the first alpha-helix and tested whether these mutants could be converted to PrP-res in both scrapie-infected neuroblastoma cells (Sc(+)-MNB cells) and a cell-free conversion assay. Removal of the second beta-strand or the first alpha-helix significantly altered both processing and the cellular localization of PrP-sen, while deletion of the first beta-strand had no effect on these events. However, all of the mutants significantly inhibited the formation of PrP-res in Sc(+)-MNB cells and had a greatly reduced ability to form protease-resistant PrP in a cell-free assay system. Thus, our results demonstrate that deletion of the beta-strands and the first alpha-helix of PrP-sen can fundamentally affect PrP-res formation and/or PrP-sen processing.
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PMID:Deletion of beta-strand and alpha-helix secondary structure in normal prion protein inhibits formation of its protease-resistant isoform. 1158 71

In infectious and familial prion disorders, neurodegeneration is often seen without obvious deposits of the scrapie prion protein (PrP(Sc)), the principal cause of neuronal death in prion disorders. In such cases, neurotoxicity must be mediated by alternative pathways of cell death. One such pathway is through a transmembrane form of PrP. We have investigated the relationship between intracellular accumulation of prion protein aggregates and the consequent up-regulation of transmembrane prion protein in a cell model. Here, we report that exposure of neuroblastoma cells to the prion peptide 106-126 catalyzes the aggregation of cellular prion protein to a weakly proteinase K-resistant form and induces the synthesis of transmembrane prion protein, the proposed mediator of neurotoxicity in certain prion disorders. The N terminus of newly synthesized transmembrane prion protein is cleaved spontaneously on the cytosolic face of the endoplasmic reticulum, and the truncated C-terminal fragment accumulates on the cell surface. Our results suggest that neurotoxicity in prion disorders is mediated by a complex pathway involving transmembrane prion protein and not by deposits of aggregated and proteinase K-resistant PrP alone.
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PMID:Prion peptide 106-126 modulates the aggregation of cellular prion protein and induces the synthesis of potentially neurotoxic transmembrane PrP. 1168 69

In transmissible spongiform encephalopathies, the cellular prion protein (PrP(C)) undergoes a conformational change from a prevailing alpha-helical structure to a beta-sheet-rich, protease-resistant isoform, termed PrP(Sc). PrP(C) has two characteristics: a high affinity for Cu(2+) and a strong pH-dependent conformation. Lines of evidence indicate that PrP(Sc) conformation is dependent on copper and that acidic conditions facilitate the conversion of PrP(C) --> PrP(Sc). In each species, PrP(Sc) exists in multiple conformations, which are associated with different prion strains. In sporadic Creutzfeldt-Jakob disease (sCJD), different biochemical types of PrP(Sc) have been identified according to the size of the protease-resistant fragments, patterns of glycosylation, and the metal-ion occupancy. Based on the site of cleavage produced by proteinase K, we investigated the conformational stability of PrP(Sc) under acidic, neutral, and basic conditions in 42 sCJD subjects. Our study shows that only one type of sCJD PrP(Sc), associated with the classical form, shows a pH-dependent conformation, whereas two other biochemical PrP(Sc) types, detected in distinct sCJD phenotypes, are unaffected by pH variations. This novel approach demonstrates the presence of three types of PrP(Sc) in sCJD.
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PMID:pH-dependent prion protein conformation in classical Creutzfeldt-Jakob disease. 1168 90

Three novel conformational isomers of mouse prion protein mPrP(23-231) were prepared by incubating the reduced mPrP(23-231) in the presence of urea at mild acidic conditions. They are stable isomers that can be separated and isolated by reversed phase HPLC. These isomers, designated mPrP-a, mPrP-b, and mPrP-c, all exist in reduced state and monomeric form. They all exhibit a high content of beta-sheet structure upon oligomerization at near-neutral pH. They are also partially resistant to proteolysis by proteinase K and chymotrypsin. These structural properties are hallmarks of pathogenic prion protein (PrP(SC)).
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PMID:Isolation of isoforms of mouse prion protein with PrP(SC)-like structural properties. 1168 49

The conversion of protease-sensitive prion protein (PrP-sen) to a high beta-sheet, protease-resistant and often fibrillar form (PrP-res) is a central event in transmissible spongiform encephalopathies (TSE) or prion diseases. This conversion can be induced by PrP-res itself in cell-free conversion reactions. The detergent sodium N-lauroyl sarkosinate (sarkosyl) is a detergent that is widely used in PrP-res purifications and is known to stimulate the PrP-res-induced conversion reaction. Here we report effects of sarkosyl and other detergents on recombinant hamster PrP-sen purified from mammalian cells under oxidizing conditions that maintain the single native disulfide bond. Low concentrations of sarkosyl (0.001-0.1%) induced aggregation of PrP-sen molecules, increased light scattering, altered fluorescence excitation and emission spectra, and enhanced the proportion of beta-sheet secondary structure according to circular dichroism and infrared spectroscopies. An enhancement of beta-sheet content was also seen with 0.001% sodium dodecyl sulfate (SDS) but not several other types of detergents. Electron microscopy revealed that sarkosyl induced the formation of both amorphous and fibrillar aggregates. The fibrils appeared to be constructed from spherical bead-like protofibrils. Neither TSE infectivity nor the characteristic partial proteinase K resistance of PrP-res was detected in the sarkosyl-induced PrP aggregates. We conclude that certain anionic detergents can disrupt the conformation of PrP-sen and induce high beta-sheet aggregates that are distinct from scrapie-associated PrP-res in terms of protease-resistance, infrared spectrum and infectivity. These results reinforce the idea that not all high-beta aggregates of PrP are equivalent to the pathologic form, PrP-res.
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PMID:Conformational change, aggregation and fibril formation induced by detergent treatments of cellular prion protein. 1170 70

Some transmissible spongiform encephalopathy (TSE) (or "prion") strains, notably those derived from bovine spongiform encephalopathy, are highly resistant to total inactivation by heat. When three TSE strains derived from sheep with scrapie were heated, little inactivation took place at low temperatures, but at higher temperatures, considerable inactivation occurred. The temperature at which substantial inactivation first occurred varied according to TSE strain, and it was calculated to be 70 degrees C for the 22C strain, 84 degrees C for ME7, and 97 degrees C for 22A by fitting the data to a model based on competition between a destructive and a protective reaction. However, PrP(Sc) from mice infected with a range of TSE strains retained similar resistance to proteinase K digestion after heating to below or above these temperatures, showing that the properties of PrP(Sc) responsible for proteinase resistance do not correlate with those conferring thermostability on the TSE agent. The simplest explanation of these data is that the causal agent contains a macromolecular component that is structurally independent of the host, that it varies covalently between TSE strains, and that it is protected by other macromolecular components. The model is in accord with the virino hypothesis, which proposes a host-independent informational molecule protected by the host protein PrP.
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PMID:Characterization of thermodynamic diversity between transmissible spongiform encephalopathy agent strains and its theoretical implications. 1179 7

Transmissible spongiform encephalopathies (TSE), or prion diseases, are mammalian neurodegenerative disorders characterized by a conformational modification of the host-encoded prion protein (PrP(C)) into an isoform which is detergent-insoluble and partially resistant to protease treatment (PrP(Sc)). Distinct types of PrP(Sc), differing in conformation and variation in the relative amount of their glycoforms, have been associated with different phenotypes of TSE. In sporadic Creutzfeldt-Jakob disease (sCJD), two major types of PrP(Sc), with proteinase K (PK)-resistant fragments of 21 and 19 kDa, have been described. No consensus exists, however, on the molecular classification of PrP(Sc) in sCJD, since further heterogeneity within PrPSc conformers has been reported. We studied 19 subjects with dementia or dementia/ataxia at onset and 12 subjects with ataxia at onset. Following two-dimensional gel electrophoresis, we characterized PrP(C) and PrP(Sc) species in normal and sCJD brains by immunoblotting with antibodies recognizing N-terminal and C-terminal PrP regions. Three types of PrP(Sc) were detected in detergent-insoluble fractions from sCJD brains, mainly consisting of full-length PrP(Sc) in subjects with rapidly progressive dementia, and two different sets of amino-truncated PrP(Sc) glycoforms in subjects with dementia/ataxia and ataxia at onset. Examination of the PrP(Sc) core fragment, following PK treatment and deglycosylation, confirmed the existence of three distinctive patterns. These findings have immediate implications for the molecular classification of sCJD.
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PMID:Two-dimensional mapping of three phenotype-associated isoforms of the prion protein in sporadic Creutzfeldt-Jakob disease. 1184 May 43

In vivo under pathological conditions, the normal cellular form of the prion protein, PrP(C) (residues 23-231), misfolds to the pathogenic isoform PrP(Sc), a beta-rich aggregated pathogenic multimer. Proteinase K digestion of PrP(Sc) leads to a proteolytically resistant core, PrP 27-30 (residues 90-231), that can form amyloid fibrils. To study the kinetic pathways of amyloid formation in vitro, we used unglycosylated recombinant PrP corresponding to the proteinase K-resistant core of PrP(Sc) and found that it can adopt two non-native abnormal isoforms, a beta-oligomer and an amyloid fibril. Several lines of kinetic data suggest that the beta-oligomer is not on the pathway to amyloid formation. The preferences for forming either a beta-oligomer or amyloid can be dictated by experimental conditions, with acidic pH similar to that seen in endocytic vesicles favoring the beta-oligomer and neutral pH favoring amyloid. Although both abnormal isoforms have high beta-sheet content and bind 1-anilinonaphthalene-8-sulfonate, they are dissimilar structurally. Multiple pathways of misfolding and the formation of distinct beta-sheet-rich abnormal isoforms may explain the difficulties in refolding PrP(Sc) in vitro, the need for a PrP(Sc) template, and the significant variation in disease presentation and neuropathology.
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PMID:Pathway complexity of prion protein assembly into amyloid. 1191 92

Conversion of the cellular isoform of the prion protein (PrP(C)) into the pathogenic isoform (PrP(Sc)) is thought to be the causative event in prion diseases. Biochemically, PrP(Sc) differs from PrP(C) in its partial resistance to proteinase K (PK). The amino acid sequence AGAAAAGA, comprising residues 112-119 of the murine PrP(C), has been shown to be amyloidogenic and evolutionarily conserved. To assess the effect of mutations at and around this hydrophobic sequence on protease resistance, the sequence was replaced either by alanines or by glycines and, in a third mutant, a large part surrounding this region was removed. The PrP mutant carrying substitutions of glycines for alanines showed PK resistance and aberrant proteolytic processing. Tetracycline-induced expression of this mutant indicated that resistance to protease is acquired concurrent with the synthesis of the protein. These findings indicate that mutations in the central hydrophobic region lead to immediate alterations in PrP structure and processing.
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PMID:Mutant prion protein acquires resistance to protease in mouse neuroblastoma cells. 1196 Dec 79


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