Surface expression of a protective recombinant pertussis toxin S1 subunit fragment in Streptococcus gordonii. (25/41883)

In this study, the expression of the Bordetella pertussis S1 subunit was tested in Streptococcus gordonii, a commensal oral bacterium which has the potential to be a live oral vaccine vehicle. The DNA fragment encoding the N-terminal 179 amino acids of the S1 subunit was ligated into the middle part of spaP, the surface protein antigen P1 gene originating from Streptococcus mutans. The resulting construct, carried on the Escherichia coli-Streptococcus shuttle vector pDL276, was introduced into S. gordonii DL-1 by natural transformation. One of the transformants (RJMIII) produced a 187-kDa protein (the predicted size of the SpaP-S1 fusion protein) which was recognized by both the anti-pertussis toxin (anti-PT) and anti-SpaP antibodies, suggesting that an in-frame fusion had been made. Results from immunogold-electron microscopic studies and cellular fractionation studies showed that the fusion protein was surface localized and was mainly associated with the cell wall of RJMIII, indicating that SpaP was able to direct the fusion protein to the cell surface. A rabbit antiserum raised against heat-killed S. gordonii RJMIII recognized the native S1 subunit of PT in Western blotting and showed a weak neutralization titer to PT by the Chinese hamster ovary cell-clustering assay. BALB/c mice immunized with the heat-killed S. gordonii RJMIII were protected from the toxic effect of PT in the leukocytosis-promoting and histamine sensitization assays. In conclusion, a fragment of the S1 subunit of PT was successfully surface expressed in S. gordonii; the recombinant S1 fragment was found to be immunogenic and could induce protection against the toxic effect of PT in mice.  (+info)

Re-entering the translocon from the lumenal side of the endoplasmic reticulum. Studies on mutated carboxypeptidase yscY species. (26/41883)

Misfolded or unassembled secretory proteins are retained in the endoplasmic reticulum (ER) and subsequently degraded by the cytosolic ubiquitin-proteasome system. This requires their retrograde transport from the ER lumen into the cytosol, which is mediated by the Sec61 translocon. It had remained a mystery whether ER-localised soluble proteins are at all capable of re-entering the Sec61 channel de novo or whether a permanent contact of the imported protein with the translocon is a prerequisite for retrograde transport. In this study we analysed two new variants of the mutated yeast carboxypeptidase yscY, CPY*: a carboxy-terminal fusion protein of CPY* and pig liver esterase and a CPY* species carrying an additional glycosylation site at its carboxy-terminus. With these constructs it can be demonstrated that the newly synthesised CPY* chain is not retained in the translocation channel but reaches its ER lumenal side completely. Our data indicate that the Sec61 channel provides the essential pore for protein transport through the ER membrane in either direction; persistent contact with the translocon after import seems not to be required for retrograde transport.  (+info)

Cloning of a bovine orphan transporter and its short splicing variant. (27/41883)

We have isolated a cDNA (bv7-3) encoding a member of the Na+,Cl(-)-dependent transporter family and its short splicing variant (bv7-3s) by screening a bovine retina cDNA library. Sequence analysis revealed that bv7-3 encodes a protein of 729 amino acids and is a bovine homologue of the rat orphan transporter v7-3-2. bv7-3s contains 265 amino acids, sharing 252 N-terminal amino acids with bv7-3. Both mRNAs for bv7-3 and bv7-3s were detected in nervous system by Northern blot analysis. In immunofluorescence analysis in transfected HEK 293T cells, myc-tagged bv7-3 was mainly detected on the plasma membrane, whereas myc-tagged bv7-3s showed a pattern of intracellular membrane staining.  (+info)

Insulin-like growth factors I and II are unable to form and maintain their native disulfides under in vivo redox conditions. (28/41883)

Insulin-like growth factor (IGF) I does not quantitatively form its three native disulfide bonds in the presence of 10 mM reduced and 1 mM oxidized glutathione in vitro [Hober, S. et al. (1992) Biochemistry 31, 1749-1756]. In this paper, we show (i) that both IGF-I and IGF-II are unable to form and maintain their native disulfide bonds at redox conditions that are similar to the situation in the secretory vesicles in vivo and (ii) that the presence of protein disulfide isomerase does not overcome this problem. The results indicate that the previously described thermodynamic disulfide exchange folding problem of IGF-I in vitro is also present in vivo. Speculatively, we suggest that the thermodynamic disulfide exchange properties of IGF-I and II are biologically significant for inactivation of the unbound growth factors by disulfide exchange reactions to generate variants destined for rapid clearance.  (+info)

An Arabidopsis 14-3-3 protein can act as a transcriptional activator in yeast. (29/41883)

The 14-3-3 proteins are a group of highly conserved and widely distributed eukaryotic proteins with diverse functions. One 14-3-3 protein, AFT1 from Arabidopsis thaliana, was found to be able to activate transcription in yeast. When fused to the DNA-binding domain of a bacterial protein LexA, AFT1 can activate transcription of reporter genes that contain LexA operator sequences in their promoters. Although the in vivo function of AFT1 is not completely known, its similarity to previously identified proteins found in transcription complexes of Arabidopsis and maize suggests that AFT1 and some other 14-3-3 proteins may activate gene expression in other systems as well.  (+info)

Receptor activator of NF-kappaB recruits multiple TRAF family adaptors and activates c-Jun N-terminal kinase. (30/41883)

Receptor activator of NF-kappaB (RANK) is a recently cloned member of the tumor necrosis factor receptor (TNFR) superfamily, and its function has been implicated in osteoclast differentiation and dendritic cell survival. Many of the TNFR family receptors recruit various members of the TNF receptor-associated factor (TRAF) family for transduction of their signals to NF-kappaB and c-Jun N-terminal kinase. In this study, the involvement of TRAF family members and the activation of the JNK pathway in signal transduction by RANK were investigated. TRAF1, 2, 3, 5, and 6 were found to bind RANK in vitro. Association of RANK with each of these TRAF proteins was also detected in vivo. Expression of RANK in cultured cells also induced the activation of JNK, which was blocked by a dominant-negative form of JNK. Furthermore, by employing various C-terminal deletion mutants of RANK, the regions responsible for TRAF interaction and JNK activation were identified. TRAF5 was determined to bind to the C-terminal 11 amino acids and the other TRAF members to a region N-terminal to the TRAF5 binding site. The domain responsible for JNK activation was localized to the same region where TRAF1, 2, 3, and 6 bound, which suggests that these TRAF molecules might mediate the RANK-induced JNK activation.  (+info)

Possible role for ligand binding of histidine 81 in the second transmembrane domain of the rat prostaglandin F2alpha receptor. (31/41883)

For the five principal prostanoids PGD2, PGE2, PGF2alpha, prostacyclin and thromboxane A2 eight receptors have been identified that belong to the family of G-protein-coupled receptors. They display an overall homology of merely 30%. However, single amino acids in the transmembrane domains such as an Arg in the seventh transmembrane domain are highly conserved. This Arg has been identified as part of the ligand binding pocket. It interacts with the carboxyl group of the prostanoid. The aim of the current study was to analyze the potential role in ligand binding of His-81 in the second transmembrane domain of the rat PGF2alpha receptor, which is conserved among all PGF2alpha receptors from different species. Molecular modeling suggested that this residue is located in close proximity to the ligand binding pocket Arg 291 in the 7th transmembrane domain. The His81 (H) was exchanged by site-directed mutagenesis to Gln (Q), Asp (D), Arg (R), Ala (A) and Gly (G). The receptor molecules were N-terminally extended by a Flag epitope for immunological detection. All mutant proteins were expressed at levels between 50% and 80% of the wild type construct. The H81Q and H81D receptor bound PGF2alpha with 2-fold and 25-fold lower affinity, respectively, than the wild type receptor. Membranes of cells expressing the H81R, H81A or H81G mutants did not bind significant amounts of PGF2alpha. Wild type receptor and H81Q showed a shallow pH optimum for PGF2alpha binding around pH 5.5 with almost no reduction of binding at higher pH. In contrast the H81D mutant bound PGF2alpha with a sharp optimum at pH 4.5, a pH at which the Asp side chain is partially undissociated and may serve as a hydrogen bond donor as do His and Gln at higher pH values. The data indicate that the His-81 in the second transmembrane domain of the PGF2alpha receptor in concert with Arg-291 in the seventh transmembrane domain may be involved in ligand binding, most likely not by ionic interaction with the prostaglandin's carboxyl group but rather as a hydrogen bond donor.  (+info)

R73A and H144Q mutants of the yeast mitochondrial cyclophilin Cpr3 exhibit a low prolyl isomerase activity in both peptide and protein-folding assays. (32/41883)

Previously we reported that the R73A and H144Q variants of the yeast cyclophilin Cpr3 were virtually inactive in a protease-coupled peptide assay, but retained activity as catalysts of a proline-limited protein folding reaction [Scholz, C. et al. (1997) FEBS Lett. 414, 69-73]. A reinvestigation revealed that in fact these two mutations strongly decrease the prolyl isomerase activity of Cpr3 in both the peptide and the protein-folding assay. The high folding activities found previously originated from a contamination of the recombinant Cpr3 proteins with the Escherichia coli protein SlyD, a prolyl isomerase that co-purifies with His-tagged proteins. SlyD is inactive in the peptide assay, but highly active in the protein-folding assay.  (+info)