Identification of a second major tumor-specific antigen recognized by CTLs on mouse mastocytoma P815.
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Murine mastocytoma P815 induces CTL responses against at least four distinct Ags (AB, C, D, and E). Recent studies have shown that the main component of the CTL response against the P815 tumor is targeted against Ags P815AB and P815E. The gene P1A has been well characterized. It encodes the P815AB Ag in the form of a nonameric peptide containing two epitopes, P815A and P815B, which are recognized by different CTLs. Here, we report the identification of the P815E Ag. Using a cDNA library derived from tumor P815, we identified the gene coding for P815E. We also characterized the antigenic peptide that anti-P815E CTLs recognize on the MHC class I molecule H-2Kd. The P815E Ag results from a mutation within an ubiquitously expressed gene encoding methionine sulfoxide reductase, an enzyme that is believed to be important in the protection of proteins against the by-products of aerobic metabolism. Surprisingly, immunizing mice i.p. with syngeneic tumor cells (L1210) that were constructed to express B7-1 and P815E did not induce resistance against live P815, even though a strong anti-P815E CTL response was observed with splenocytes from immunized animals. (+info)
Diastereoselective reduction of protein-bound methionine sulfoxide by methionine sulfoxide reductase.
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Methionine sulfoxide (MetSO) in calmodulin (CaM) was previously shown to be a substrate for bovine liver peptide methionine sulfoxide reductase (pMSR, EC 1.8.4.6), which can partially recover protein structure and function of oxidized CaM in vitro. Here, we report for the first time that pMSR selectively reduces the D-sulfoxide diastereomer of CaM-bound L-MetSO (L-Met-D-SO). After exhaustive reduction by pMSR, the ratio of L-Met-D-SO to L-Met-L-SO decreased to about 1:25 for hydrogen peroxide-oxidized CaM, and to about 1:10 for free MetSO. The accumulation of MetSO upon oxidative stress and aging in vivo may be related to incomplete, diastereoselective, repair by pMSR. (+info)
Molecular cloning and functional expression of a human peptide methionine sulfoxide reductase (hMsrA).
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Oxidation of methionine residues in proteins to methionine sulfoxide can be reversed by the enzyme peptide methionine sulfoxide reductase (MsrA, EC 1.8.4.6). We cloned the gene encoding a human homologue (hMsrA) of the enzyme, which has an 88% amino acid sequence identity to the bovine version (bMsrA). With dot blot analyses based on RNA from human tissues, expression of hMsrA was found in all tissues tested, with highest mRNA levels in adult kidney and cerebellum, followed by liver, heart ventricles, bone marrow and hippocampus. In fetal tissue, expression was highest in the liver. No expression of hmsrA was detected in leukemia and lymphoma cell lines. To test if hMsrA is functional in cells, we assayed its effect on the inactivation time course of the A-type potassium channel ShC/B since this channel property strongly depends on the oxidative state of a methionine residue in the N-terminal part of the polypeptide. Co-expression of ShC/B and hMsrA in Xenopus oocytes significantly accelerated inactivation, showing that the cloned enzyme is functional in an in vivo assay system. Furthermore, the activity of a purified glutathione-S-transferase-hMsrA fusion protein was demonstrated in vitro by measuring the reduction of [3H]N-acetyl methionine sulfoxide. (+info)
Inactivation of MXR1 abolishes formation of dimethyl sulfide from dimethyl sulfoxide in Saccharomyces cerevisiae.
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Dimethyl sulfide (DMS) is a sulfur compound of importance for the organoleptic properties of beer, especially some lager beers. Synthesis of DMS during beer production occurs partly during wort production and partly during fermentation. Methionine sulfoxide reductases are the enzymes responsible for reduction of oxidized cellular methionines. These enzymes have been suggested to be able to reduce dimethyl sulfoxide (DMSO) as well, with DMS as the product. A gene for an enzymatic activity leading to methionine sulfoxide reduction in Saccharomyces yeast was recently identified. We confirmed that the Saccharomyces cerevisiae open reading frame YER042w appears to encode a methionine sulfoxide reductase, and propose the name MXR1 for the gene. We found that Mxr1p catalyzes reduction of DMSO to DMS and that an mxr1 disruption mutant cannot reduce DMSO to DMS. Mutant strains appear to have unchanged fitness under several laboratory conditions, and in this paper I hypothesize that disruption of MXR1 in brewing yeasts would neutralize the contribution of the yeast to the DMS content in beer. (+info)
New mammalian selenocysteine-containing proteins identified with an algorithm that searches for selenocysteine insertion sequence elements.
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Mammalian selenium-containing proteins identified thus far contain selenium in the form of a selenocysteine residue encoded by UGA. These proteins lack common amino acid sequence motifs, but 3'-untranslated regions of selenoprotein genes contain a common stem-loop structure, selenocysteine insertion sequence (SECIS) element, that is necessary for decoding UGA as selenocysteine rather than a stop signal. We describe here a computer program, SECISearch, that identifies mammalian selenoprotein genes by recognizing SECIS elements on the basis of their primary and secondary structures and free energy requirements. When SECISearch was applied to search human dbEST, two new mammalian selenoproteins, designated SelT and SelR, were identified. We determined their cDNA sequences and expressed them in a monkey cell line as fusion proteins with a green fluorescent protein. Incorporation of selenium into new proteins was confirmed by metabolic labeling with (75)Se, and expression of SelT was additionally documented in immunoblot assays. SelT and SelR did not have homology to previously characterized proteins, but their putative homologs were detected in various organisms. SelR homologs were present in every organism characterized by complete genome sequencing. The data suggest applicability of SECISearch for identification of new selenoprotein genes in nucleotide data bases. (+info)
Reactive oxygen species and nitric oxide mediate plasticity of neuronal calcium signaling.
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Reactive oxygen species (ROS) and nitric oxide (NO) are important participants in signal transduction that could provide the cellular basis for activity-dependent regulation of neuronal excitability. In young rat cortical brain slices and undifferentiated PC12 cells, paired application of depolarization/agonist stimulation and oxidation induces long-lasting potentiation of subsequent Ca(2+) signaling that is reversed by hypoxia. This potentiation critically depends on NO production and involves cellular ROS utilization. The ability to develop the Ca(2+) signal potentiation is regulated by the developmental stage of nerve tissue, decreasing markedly in adult rat cortical neurons and differentiated PC12 cells. (+info)
HIV-2 protease is inactivated after oxidation at the dimer interface and activity can be partly restored with methionine sulphoxide reductase.
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Human immunodeficiency viruses encode a homodimeric protease that is essential for the production of infectious virus. Previous studies have shown that HIV-1 protease is susceptible to oxidative inactivation at the dimer interface at Cys-95, a process that can be reversed both chemically and enzymically. Here we demonstrate a related yet distinct mechanism of reversible inactivation of the HIV-2 protease. Exposure of the HIV-2 protease to H(2)O(2) resulted in conversion of the two methionine residues (Met-76 and Met-95) to methionine sulphoxide as determined by amino acid analysis and mass spectrometry. This oxidation completely inactivated protease activity. However, the activity could be restored (up to 40%) after exposure of the oxidized protease to methionine sulphoxide reductase. This treatment resulted in the reduction of methionine sulphoxide 95 but not methionine sulphoxide 76 to methionine, as determined by peptide mapping/mass spectrometry. We also found that exposure of immature HIV-2 particles to H(2)O(2) led to the inhibition of polyprotein processing in maturing virus particles comparable to that demonstrated for HIV-1 particles. Thus oxidative inactivation of the HIV protease in vitro and in maturing viral particles is not restricted to the type 1 proteases. These studies indicate that two distinct retroviral proteases are susceptible to inactivation after a very minor modification at residue 95 of the dimer interface and suggest that the dimer interface might be a viable target for the development of novel protease inhibitors. (+info)
Expression of UGA-containing Mycoplasma genes in Bacillus subtilis.
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We used Bacillus subtilis to express UGA-containing Mycoplasma genes encoding the P30 adhesin (one UGA) of Mycoplasma pneumoniae and methionine sulfoxide reductase (two UGAs) of Mycoplasma genitalium. Due to natural UGA suppression, these Mycoplasma genes were expressed as full-length protein products, but at relatively low efficiency, in recombinant wild-type Bacillus. The B. subtilis-expressed Mycoplasma proteins appeared as single bands and not as multiple bands compared to expression in recombinant Escherichia coli. Bacillus mutants carrying mutations in the structural gene (prfB) for release factor 2 markedly enhanced the level of readthrough of UGA-containing Mycoplasma genes. (+info)