[Show abstract][Hide abstract] ABSTRACT: Current influenza vaccines are produced in embryonated chicken eggs. However, egg-based vaccines have various problems. To address these problems, recombinant protein vaccines have been developed as new vaccine candidates. Unfortunately, recombinant proteins frequently encounter aggregation and low stability during their biogenesis. It has been previously demonstrated that recombinantly expressed proteins can be greatly stabilized with high solubility by fusing stabilizing peptide (SP) derived from the c-terminal acidic tail of human synuclein (ATS). To investigate whether SP fusion proteins can induce protective immunity in mice, we produced influenza HA and SP fusion protein using baculovirus expression system. In in vitro tests, SP-fused recombinant HA1 (SP-rHA1) was shown to be more stable than recombinant HA1 (rHA1). Mice were immunized intramuscularly with baculovirus-expressed rHA1 protein or SP-rHA1 protein (2ug/mouse) formulated with aluminum hydroxide. Antibody responses were determined by ELISA and hemagglutination inhibition assay. We observed that SP-rHA1 immunization elicited HA-specific antibody response that was comparable to rHA1 immunization. These results indicate that fusion of SP to rHA1 does not negatively affect the immunogenicity of the vaccine candidate. Therefore, it is possible to apply SP fusion technology to develop stable recombinant protein vaccines with high solubility.
Full-text · Article · Nov 2014 · Journal of Microbiology and Biotechnology
[Show abstract][Hide abstract] ABSTRACT: The major factors and mechanisms by which natural killer (NK) cells are inhibited in cancer patients have not yet been well defined. In this study, we conducted a comparative analysis of the effects of TGF- β, IL-10, and IL-4 on primary NK cells, and it was demonstrated that (1) TGF-β most potently inhibited the overall function of NK cells. (2) It appears that TGF-β reduced the tyrosine phosphorylation of Syk and the expression of c-myc. (3) It was also found that the IL-2-induced promoter-binding activities of C-myb, AP-1, CREB, and AR were also completely suppressed upon TGF-β treatment. Interestingly, TGF-β also completely suppressed other transcription factors, which are constitutively activated. Among these factors, we further confirmed roles of AP-1 in NK-92 cell activation through c-jun and MEK1 inhibitor assay. Our study provides insight into the effects of TGF-β in modulating NK cell functions.
No preview · Article · Jul 2014 · Cellular Immunology
[Show abstract][Hide abstract] ABSTRACT: Natural killer (NK) cells are lymphocytes of the innate immune system and have the ability to kill tumor cells and virus-infected cells without prior sensitization. Malignant tumors and viruses have developed, however, strategies to suppress NK cells to escape from their responses. Thus, the evaluation of NK cell activity (NKA) could be invaluable to estimate the status and the outcome of cancers, viral infections, and immune-mediated diseases. Established methods that measure NKA, such as (51)Cr release assay and CD107a degranulation assay, may be used to determine NK cell function, but they are complicated and time-consuming because they require isolation of peripheral blood mononuclear cells (PBMC) or NK cells. In some cases these assays require hazardous material such as radioactive isotopes. To overcome these difficulties, we developed a simple assay that uses whole blood instead of PBMC or isolated NK cells. This novel assay is suitable for high-throughput screening and the monitoring of diseases, because it employs serum of ex vivo stimulated whole blood to detect interferon (IFN)-γ secreted from NK cells as an indicator of NKA. After the stimulation of NK cells, the determination of IFNγ concentration in serum samples by enzyme-linked immunosorbent assay (ELISA) provided a swift, uncomplicated, and high-throughput assay of NKA ex vivo. The NKA results microsatellite stable (MSS) colorectal cancer patients was showed significantly lower NKA, 263.6±54.5pg/mL compared with healthy subjects, 867.5±50.2pg/mL (p value <0.0001). Therefore, the NKA could be utilized as a supportive diagnostic marker for microsatellite stable (MSS) colorectal cancer.
No preview · Article · Mar 2014 · Biochemical and Biophysical Research Communications
[Show abstract][Hide abstract] ABSTRACT: Natural killer cells are lymphocytes of the innate immune system that play a key role in the direct elimination of transformed or virus-infected cells. Recently, it has been reported that NK cells can attack cancer cells with stem cell-like properties. In this study, we isolated ovarian cancer cell lines CAOV3 and TOV21G with and without CD24, which has been reported as an ovarian cancer stem cell marker, and compared their drug resistance and susceptibility to NK cell lysis. The isolated CD24(+) CAOV3 and TOV21G cells were more resistant to cisplatin and doxorubicin anti-cancer drugs. Also, CD24(+) CAOV3 and TOV21G cells were more susceptible to NK cell lysis compared with CD24(-) cells. In order to identify reasons for the differing NK cell susceptibility, we examined NK cell-killing mechanisms against CD24(+) cancer cell lines by analyzing NKG2D ligands, MHC class I molecules, and natural cytotoxic receptor ligands expression on target cells. Consistently, CD24(+) CAOV3 and TOV21G cells showed up-regulated NKG2D ligands and down-regulated MHC class I molecule expression. These findings show that CD24(+) ovarian cancer cell lines are more resistant to antitumor drugs but are more susceptible to NK cell lysis; thus, NK cell immunotherapy might be useful in eliminating ovarian cancer stem cells and preventing tumor recurrence and metastasis.
No preview · Article · Sep 2012 · Biochemical and Biophysical Research Communications
[Show abstract][Hide abstract] ABSTRACT: α-Synuclein is the principal component of the Lewy body deposits that are characteristic of Parkinson's disease. In vivo, and under physiological conditions in vitro, α-synuclein aggregates to form amyloid fibrils, a process that is likely to be associated with the development of Parkinson's disease. α-Synuclein also possesses chaperone activity to prevent the precipitation of amorphously aggregating target proteins, as demonstrated in vitro. α-Synuclein is an intrinsically disordered (i.e., unstructured) protein of 140 amino acids in length, and therefore studies on its fragments can be correlated directly to the functional role of these regions in the intact protein. In this study, the fragment containing residues 61-140 [α-syn(61-140)] was observed to be highly amyloidogenic and was as effective a chaperone in vitro as the full-length protein, while the N- and C-terminal fragments α-syn(1-60) and α-syn(96-140) had no intrinsic chaperone activity. Interestingly, full-length fibrillar α-synuclein had greater chaperone activity than nonfibrillar α-synuclein. It is concluded that the amyloidogenic NAC region (residues 61-95) contains the chaperone-binding site which is optimized for target protein binding as a result of its β-sheet formation and/or ordered aggregation by α-synuclein. On the other hand, the first 60 residues of α-synuclein modulate the protein's chaperone-active site, while at the same time protecting α-synuclein from fibrillation. On its own, however, this fragment [α-syn(1-60)] had a tendency to aggregate amorphously. As a result of this study, the functional roles of the various regions of α-synuclein in its chaperone activity have been delineated.
Full-text · Article · May 2012 · Proteins Structure Function and Bioinformatics
[Show abstract][Hide abstract] ABSTRACT: α-Synuclein, a presynaptic protein of the central nervous system, has been implicated in the synaptic events such as neuronal
plasticity during development and learning, and neuronal degeneration under pathological conditions. As an effort to understand
the biological function of α-synuclein, we examined the expression patterns of α-synuclein in various human hematopoietic
cells, and in Drosophila at different developmental stages. The α-synuclein was ubiquitously expressed in all the tested hematopoietic cells including
T cells, B cells, NK cells, and monocytes, as well as in the lymphoma cell lines, Jurkat and K562. A potential α-synuclein
homologue was also expressed in Drosophila, and its expression appeared to be temporally and spatially regulated during development. Our data suggest that α-synuclein
may function in invertebrates as well as in vertebrates and its function may not be restricted to the neuron.
KeywordsDevelopment-Gene Expression-NACP-Neurodegenerative Disease-Synuclein-Synuclein
Full-text · Article · Apr 2012 · Molecules and Cells
[Show abstract][Hide abstract] ABSTRACT: The synuclein family consists of three distinct genes, α-synuclein, β-synuclein, and γ-synuclein. The α-synuclein and β-synuclein are predominately expressed in brain and especially α-synuclein is related with Parkinson's disease, Alzheimer's disease, and dementia with Lewy bodies. The γ-synuclein was first identified as breast cancer specific gene 1. It is expressed in the peripheral nervous system and also detected in breast and ovarian cancers. The γ-synuclein is also known to mediate metastasis of breast and ovarian cancer cells. Insulin-like growth factor 1 (IGF-I) is one of the growth factors that plays an important role in cell proliferation and migration in cancer cells, as well as in normal cells. In this study, we investigated the migrations of SKOV-3, MDAMB-231, and HeLa cells by the recombinant synuclein proteins (α-, β-, and γ-synucleins) and IGF-I and the molecular mechanism. Furthermore, we investigated the membrane ruffle formation of SKOV-3 cells by recombinant synuclein proteins and IGF-I. As a result, synucleins and IGF-I were found to induce cancer cell migrations. Simultaneous synucleins and IGF-I treatment on the cancer cells induced more migrations than the individual synuclein or IGF-I treatments. The synucleins or IGF-I treatments increased the expressions of membrane-type1 matrix metalloproteinase (MT1-MMP) and cluster of differentiation 44 (CD44). Moreover, simultaneous synucleins and IGF-I treatments further increased the expressions of MT1-MMP and CD44. The synucleins and IGF-I promoted the conformational change of actin filaments, and then this led to the membrane ruffle formation.
Preview · Article · Jan 2012 · Journal of Bacteriology and Virology
[Show abstract][Hide abstract] ABSTRACT: Although previous studies on hexokinase (HK) II indicate both the N- and C-terminal halves are catalytically active, we show in this study the N-terminal half is significantly more catalytic than the C-terminal half in addition to having a significantly higher Km for ATP and Glu. Furthermore, truncated forms of intact HK II lacking its first N-terminal 18 amino acids (delta18) and a truncated N-terminal half lacking its first 18 amino acids (delta18N) have higher catalytic activity than other mutants tested. Similar results were obtained by PET-scan analysis using (18)FFDG. Our results collectively suggest that each domain of HK II possesses enzyme activity, unlike HK I, with the N-terminal half showing higher enzyme activity than the C-terminal half.
[Show abstract][Hide abstract] ABSTRACT: ALpha-synuclein (alpha-syn) has been known to be a key player of the pathogenesis of Parkinson's disease and has recently been detected in extracellular biological fluids and shown to be rapidly secreted from cells. The penetration of alpha-syn into cells has also been observed. In this study, we observed that dl-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol, a glucosyltransferase inhibitor, and proteinase K inhibited the internalization of extracellular monomeric alpha-syn into BV-2 cells, and the addition of monosialoganglioside GM1 ameliorated the inhibition of alpha-syn internalization in dl-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol-treated BV-2 cells. Furthermore, inhibition of clathrin-, caveolae-, and dynamin-dependent endocytosis did not prevent the internalization of alpha-syn, but disruption of lipid raft inhibited it. Inhibition of macropinocytosis and disruption of actin and microtubule structures also did not inhibit the internalization of alpha-syn. In addition, we further confirmed these observations by co-culture system of BV-2 cells and alpha-syn-over-expressing SH-SY5Y cells. These findings suggest that extracellular alpha-syn is internalized into microglia via GM1 as well as hitherto-unknown protein receptors in clathrin-, caveolae-, and dynamin-independent, but lipid raft-dependent manner. Elucidation of the mechanism involved in internalization of alpha-syn should be greatly helpful in the development of new treatments of alpha-syn-related neurodegenerative diseases.
Full-text · Article · Jun 2009 · Journal of Neurochemistry
[Show abstract][Hide abstract] ABSTRACT: Natural cytotoxicity receptors (NCRs) are major activating receptors involved in NK cytotoxicity. NCR expression varies with the activation state of NK cells, and the expression level correlates with NK cells' natural cytotoxicity. In this study, we found that Gö6983, a PKC inhibitor, induced a remarkable increase of NCR expression on primary NK cells, but other PKC inhibitors and NK cell stimulators such as IL-2 and PMA, did not. Gö6983 increased the expression of NCR in a time- and concentration-dependent manner. Furthermore, Gö6983 strongly upregulated the surface expression of death ligands FasL and TRAIL, but not cytotoxic molecules perforin and granzyme B. Unlike two other NK stimulating molecules, IL-2, and PMA, Gö6983 did not induce NK cell proliferation. Up-regulation of NCRs and death ligands on NK cells by Gö6983 resulted in a significant enhancement of NK cytotoxicity against various cancer cell lines. Most importantly, administration of Gö6983 effectively inhibited pulmonary tumor metastasis in mice in a dose-dependent manner. These results suggest that Gö6983 functions as an NK cell activating molecule (NKAM); this NKAM is a novel anti-cancer and anti-metastasis drug candidate because it enhances NK cytotoxicity against cancer cells in vivo as well as in vitro.
No preview · Article · Apr 2009 · Cancer Immunology and Immunotherapy
[Show abstract][Hide abstract] ABSTRACT: Alpha-synuclein (Syn) is implicated in the pathogenesis of PD and related neurodegenerative disorders. Recent studies have also shown that alpha-synuclein can activate microglia and enhance dopaminergic neurodegeneration. The mechanisms of microglia activation by alpha-synuclein, however, are not well understood. In this study, we found that not only alpha-synuclein but also beta- and gamma-synucleins activated macrophages (RAW 264.7) in vitro. Macrophages treated with synuclein proteins secreted TNF-alpha in a dose-dependent manner. Synuclein family proteins also increased mRNA transcription of COX-2 and iNOS. Two alpha-synuclein deletion mutants, SynDeltaNAC and Syn61-140, activated macrophages, while deletion mutants Syn1-60 and Syn96-140 did not significantly activate them. Finally, we demonstrated that macrophage activation by alpha-synuclein was accompanied by phosphorylation of ERK. These results suggest that synuclein family proteins can activate macrophages, and that macrophage activation needs both the N-terminal and C-terminal domains of alpha-synuclein, but not the central NAC region.
Full-text · Article · Apr 2009 · Biochemical and Biophysical Research Communications
[Show abstract][Hide abstract] ABSTRACT: Human interferon alpha-1 (hIFNA1) is one of several interferon alpha subtypes that have been studied and commercialized to treat various viral diseases including hepatitis B and C as well as malignant melanoma. Protein aggregation has been problematic for every step in commercial production, from purification to the packaging and delivery of pharmaceutical proteins. In a previous study, we demonstrated that a stabilizing peptide from the C-terminal acidic tail of alpha-synuclein (ATS) could be used as an effective fusion tag to increase the stability of target proteins such as human growth hormone (hGH) and granulocyte colony-stimulating factor (G-CSF). In this study, we applied this ATS fusion system to hIFNA1 in order to protect against the aggregation of hIFNA1 by environmental stresses, since hIFNA1 aggregates elicit an undesirable immune response in humans. As expected, ATS-fused hIFNA1 (hIFNA1-ATS) protein showed enhanced stability against thermal stress, agitation stress, and repetitive freeze/thawing stress in comparison with native hIFNA1. More importantly, hIFNA1-ATS fusion protein appeared to be 1.6 times more active than hIFNA1 in a cell anti-proliferation assay. Furthermore, the solubility of hIFNA1-ATS appeared to be 1.7 times higher than that of native protein. Our results suggest that the ATS-tag system could be a useful means for protecting hIFNA1 protein from aggregation by various external stresses and could be used to increase the solubility of protein.
No preview · Article · Nov 2008 · Protein Expression and Purification
[Show abstract][Hide abstract] ABSTRACT: alpha-Synuclein is the major amyloidogenic component observed in the Lewy bodies of Parkinson's disease. Amyloid fibrils of alpha-synuclein prepared in vitro were instantaneously disintegrated by dequalinium (DQ). Double-headed cationic amphipathic structure of DQ with two aminoquinaldinium rings at both ends turned out to be crucial to exert the disintegration activity. The defibrillation activity was shown to be selective toward the fibrils of alpha-synuclein and Abeta40 while the other beta2-microglobulin amyloid fibrils were not susceptible so much. Besides the common cross beta-sheet conformation of amyloid fibrils, therefore, additional specific molecular interactions with the target amyloidogenic proteins have been expected to be involved for DQ to exhibit its defibrillation activity. The disintegrating activity of DQ was also evaluated in vivo with the yeast system overexpressing alpha-synuclein-GFP. With the DQ treatment, the intracellular green inclusions turned into green smears, which resulted in the enhanced cell death. Based on the data, the previous observation that DQ led to the predominant protofibril formation of alpha-synuclein could be explained by the dual function of DQ showing both the facilitated self-oligomerization of alpha-synuclein and the instantaneous defibrillation of its amyloid fibrils. In addition, amyloidosis-related cytotoxicity has been demonstrated to be amplified by the fragmentation of mature amyloid fibrils by DQ.
Full-text · Article · Nov 2008 · Biochimica et Biophysica Acta
[Show abstract][Hide abstract] ABSTRACT: Down syndrome is mainly caused by a trisomy of chromosome 21. The Down syndrome critical region 2 (DSCR2) gene is located within a part of chromosome 21, the Down syndrome critical region (DSCR). To investigate the function of DSCR2, we sought to identify DSCR2-interacting proteins using yeast two-hybrid assays. A human fetal brain cDNA library was screened, and DSCR2 was found to interact with a member of the nuclear receptor superfamily, peroxisome proliferator-activated receptor beta, (PPARbeta). A co-immunoprecipitation assay demonstrated that DSCR2 physically interacts with PPARbeta in mammalian HEK293 cells. DSCR2 also inhibited the ligand-induced transcriptional activity of PPARbeta. Furthermore, PPARbeta also decreased the solubility of DSCR2, which increased levels of insoluble DSCR2.
Full-text · Article · Oct 2008 · Biochemical and Biophysical Research Communications
[Show abstract][Hide abstract] ABSTRACT: Activation-induced upregulation of inhibitory killer Ig-like receptor (KIR) is regulated by protein kinase Cs (PKCs). Conventional PKCs increase KIR expression on the post-transcriptional level by increasing the recycling of surface molecules and endoplasmic reticulum (ER)-Golgi processing. PKCdelta plays a role in the secretion of cytoplasmic KIR through lytic granules. In this study, we identified amino acid sequence motifs associated with PKC-mediated KIR membrane trafficking by systematic mutagenesis. Mutations of Y(398) and HLWC(364) completely inhibited the PMA-induced increase of KIR molecules at surface as well as total protein levels, indicating that these are associated with ER-Golgi processing and sorting to plasma membrane through lytic granules. Mutations of Y-based motif, including Y(398), acidic region (PE(394)), dileucine motif-like region (IL(423)) and PKC-phosphorylatable S(415) caused a blockade of surface KIR endocytosis after PKC stimulation. Mutation of T(145) caused an accumulation of mutant proteins in late endosomes and lysosomes after PKC activation, suggesting that T(145) might be related to the recovery of endocytosed KIR to the surface membrane. We also demonstrated that PKCs could directly phosphorylate the KIR cytoplasmic tail by means of western blot and in vitro kinase assay, implying that phosphorylation status of KIR cytoplasmic tail can direct the fate of surface KIR molecules. Taken together, various sequence motifs are implicated in the PKC-mediated post-transcriptional upregulation of KIR, and each of these motifs work in different steps after PKC activation.
Preview · Article · Feb 2008 · Immunology and Cell Biology
[Show abstract][Hide abstract] ABSTRACT: Hemorrhagic fever with renal syndrome (HFRS) is a rodent-borne viral zoonosis characterized by fever, hemorrhagic manifestations, and renal disorder. The causative agent of HFRS has been identified as a hantavirus. Hantavirus nucleocapsid proteins have recently been shown to be immunodominant antigens in HFRS, inducing an early and long-lasting immune response, and their amino termini are sensitive tools for the detection of specific antibodies in HFRS patient sera. Previous work has demonstrated that the introduction of the acidic tail of alpha-synuclein (ATS) into heat-labile proteins protects them from heat-induced aggregation. In this study, the ATS peptide was introduced into the N-terminal antigenic portion of the nucleocapsid proteins (amino acid residues 1-70) of the Hantaan virus (HTNV-delta N) and Seoul virus (SEOV-delta N). The recombinant ATS-HTNV-delta N and ATS-SEOV-delta N fusion proteins were heat-resistant, and the proteins purified by heat treatment were immunoreactive to sera from patients with HFRS. Compared with sera from patients with leptospirosis and scrub typhus, sera from patients with HFRS showed much higher reactivity in ATS-HTNV-delta N- or ATS-SEOV-delta N-based IgG ELISAs. Immunoblotting analysis revealed that only sera from patients with HFRS specifically recognized the ATS-HTNV-delta N and ATS-SEOV-delta N, indicating that the ATS-HTNV-delta N and ATS-SEOV-delta N were highly purified species without any other immunoreactive proteins as contaminants. These data demonstrate that the ATS-HTNV-delta N and ATS-SEOV-delta N fusion proteins offer a safe and inexpensive source of pure and specific antigen for large-scale diagnosis and seroepidemiological studies of HFRS, and that ATS-fusion technology can also be utilized to solubilize other antigens that could be used for large-scale diagnosis and seroepidemiological studies of other diseases.
No preview · Article · Feb 2008 · Journal of Virological Methods
[Show abstract][Hide abstract] ABSTRACT: The protein BigH3 is a cell-adhesion molecule induced by transforming growth factor-beta (TGF-beta). It consists of four homologous repeat domains known as FAS1 domains; mutations in these domains have been linked to corneal dystrophy. The fourth FAS1 domain was expressed in Escherichia coli B834 (DE3) (a methionine auxotroph) and purified by DEAE anion-exchange and gel-filtration chromatography. The FAS1 domain was crystallized using the vapour-diffusion method. A SAD diffraction data set was collected to a resolution of 2.5 A at 100 K. The crystal belonged to space group P6(1) or P6(5) and had two molecules per asymmetric unit, with unit-cell parameters a = b = 62.93, c = 143.27 A, alpha = beta = 90.0, gamma = 120.0 degrees.
Preview · Article · Nov 2007 · Acta Crystallographica Section F Structural Biology and Crystallization Communications
[Show abstract][Hide abstract] ABSTRACT: Inhibitory killer Ig-like receptor (KIR) expression was upregulated by protein kinase C (PKC) activation in stable Jurkat clones that express KIR or CD8KIR fusion proteins. PKC-induced KIR upregulation was mediated by the cytoplasmic tail of KIR and regulated at the post-transcriptional level. PKC inhibition, metabolic labeling and colocalization studies demonstrated that the activation of the conventional PKCs upregulated surface and cellular KIR levels by stimulating the maturation processes in endoplasmic reticulum-Golgi and by promoting the recycling of surface KIR through sorting endosomes. Similar studies also revealed that KIR was secreted to plasma membrane through lytic granules in a PKCdelta-dependent manner. Consequently, PKCdelta inhibition caused the formation of giant perinuclear granules, which trapped KIR and FasL as well as CPE and Lamp1.
Preview · Article · Jan 2007 · Immunology and Cell Biology
[Show abstract][Hide abstract] ABSTRACT: Lewy bodies (LBs) are pathological hallmarks of Parkinson disease (PD) but also occur in Alzheimer disease (AD) and dementia of LBs. Alpha-synuclein, the major component of LBs, is observed in the brain of Down syndrome (DS) patients with AD. Dyrk1A, a dual specificity tyrosine-regulated kinase (Dyrk) family member, is the mammalian ortholog of the Drosophila minibrain (Mnb) gene, essential for normal postembryonic neurogenesis. The Dyrk1A gene resides in the human chromosome 21q22.2 region, which is associated with DS anomalies, including mental retardation. In this study, we examined whether Dyrk1A interacts with alpha-synuclein and subsequently affects intracellular alpha-synuclein inclusion formation in immortalized hippocampal neuronal (H19-7) cells. Dyrk1A selectively binds to alpha-synuclein in transformed and primary neuronal cells. Alpha-synuclein overexpression, followed by basic fibroblast growth factor-induced neuronal differentiation, resulted in cell death. We observed that accompanying cell death was increased alpha-synuclein phosphorylation and intracytoplasmic aggregation. In addition, the transfection of kinase-inactive Dyrk1A or Dyrk1A small interfering RNA blocked alpha-synuclein phosphorylation and aggregate formation. In vitro kinase assay of anti-Dyrk1A immunocomplexes demonstrated that Dyrk1A could phosphorylate alpha-synuclein at Ser-87. Furthermore, aggregates formed by phosphorylated alpha-synuclein have a distinct morphology and are more neurotoxic compared with aggregates composed of unmodified wild type alpha-synuclein. These findings suggest alpha-synuclein inclusion formation regulated by Dyrk1A, potentially affecting neuronal cell viability.
Full-text · Article · Dec 2006 · Journal of Biological Chemistry
[Show abstract][Hide abstract] ABSTRACT: Alpha-synuclein is a pathological component of Parkinson's disease by participating in Lewy body formation. Imbalance in protein turnover could result in the abnormal protein aggregation responsible for eventual neuronal cell death. This in vitro digestion study showed that both m-calpain and 20S proteasome preferentially hydrolyzed the N-terminal half of alpha-synuclein, which made the hydrophobic NAC and following acidic C-terminal region resistant against the proteolyses. Since the acidic C-terminal region contains the PEST segment-a protein degradation signal enriched with amino acids of proline (P), glutamate (E), serine (S), and threonine (T)-, the PEST segment has not been processed or even required for the proteolyses. Alpha-synuclein would be recognized primarily by m-calpain since the common substrate was processed by m-calpain five times more effectively than 20S proteasome with k(cat)/K(m) of 1.64 x 10(4)M(-1)s(-1) and 0.32 x 10(4) M(-1)s(-1), respectively. The N-terminally truncated protease-resistant C-terminal fragment of alpha-syn61-140 was demonstrated to stimulate the 20S proteasome-mediated breakdown of alpha-synuclein and its mutant forms of Ala53Thr and Ala30Pro. The stimulation for Ala53Thr, however, was noticeably less efficient than those for the other proteins, which might support the previous observation of the prolonged intracellular life span of Ala53Thr by 1.5-fold compared to that of wild-type form. We have hypothesized that the N-terminally truncated C-terminal fragment derived from the abundant alpha-synuclein through intracellular proteolyses could be involved in various physiological or pathological effects which might be related to the formation of abnormal protein aggregation and subsequent neuronal degeneration by influencing the intracellular protein turnover or directly participating in the aggregate formation.
Full-text · Article · Dec 2006 · Archives of Biochemistry and Biophysics