Mutations in the processing site of the precursor of ribulose-1,5-bisphosphate carboxylase/oxygenase small subunit: effects on import,processing, assembly and stability

The small subunit (SSU) of Rubisco is synthesized in the cytosol in a precursor form. Upon import into the chloroplast, it is proteolytically processed at a Cys-Met bond to yield the mature form of the protein. To assess the importance of the Met residue for recognition and processing by the stromal peptidase, we substituted this residue with either Thr, Arg or Asp. The mutant precursor proteins were imported into isolated chloroplasts, and the products of the import reactions were analyzed. Mutants containing Thr or Arg residues at the putative processing site were processed to a single peptide, comigrating with the wild-type protein. N-terminal radio-sequencing revealed that these mutants were processed at the Cys-Thr and the Cys-Arg bond, respectively. After import of the Asp-containing mutant, four processed forms of the protein were observed. Analysis of the most abundant one, co-migrating with the wild-type protein, demonstrated that this species was also a product of correct processing, at the Cys-Asp bond. All the correctly processed peptides were found to be associated with the holoenzyme of Rubisco, and remained stable within the chloroplast, like the wild-type protein. The results of this study, together with previous ones, suggest that proper recognition and processing of the SSU precursor are more affected by residues N-terminal to the processing site than by the residue on the C-terminal side of this site.     

Sporulation: an alternative way to recover recombinant proteins from Bacillus subtilis

A recombinant strain of Bacillus subtilis engineered for endocellular expression of human interleukin-1 receptor antagonist (IL-Ira) was subjected to sporulation. The recombinant protein was recovered from the sporulation supernatant in quantities, purity, and activity comparable with those obtained from a traditional cell lysate. Thus, exploitation of this natural mechanism of autolysis could overcome problems of intact protein recovery related to the cell disruption step. (c) 1995 John Wiley & Sons, Inc.     

Proteolytic cleavage of recombinant two-chain factor VIII during cell culture production is mediated by protease(s) from lysed cells. The use of pulse labelling directly in production medium

During the production by mammalian cells of recombinant factor VIII from which the B domain was deleted (rFVIII), proteolytic cleavages in the C-terminal part of the heavy chain were observed (Kjalke et al., 1995). By radioactive pulse labelling it was investigated whether the cleavages took place inside the cells during protein synthesis or after release in the medium. The rFVIII-producing CHO (Chinese hamster ovary) cells were cultured in the presence of ³⁵S-methionine and then the cell lysate and the conditioned media were immunoprecipitated and analyzed by electrophoresis. By pulse labelling and chasing for various time periods, it was shown that the cleavages only took place after secretion of the protein from the cells. Adding cell lysate to uncleaved rFVIII caused cleavage of the heavy chain, as seen by loss of binding to a monoclonal antibody specific for intact rFVIII, indicating that the cleavage was performed by proteinase(s) released from the lysed cells. By incubating intact rFVIII with the multicatalytic proteinase (proteasome) present in cytoplasm and nucleus of eukaryotic cells, loss of binding to the monoclonal antibody was observed. This indicates that the multicatalytic proteinase, released from lysed rFVIII producing cells, could be responsible for the cleavage of rFVIII. Among several protease inhibitors tested, only bacitracin was found to diminish the extent of cleavage. Phosphatidylserine also protected rFVIII against cleavage, probably by binding to rFVIII. This revised version was published online in July 2006 with corrections to the Cover Date.     

Dynamic properties of some β-chain mutant hemoglobins

The thermal behavior of the Soret band relative to the carbonmonoxy derivatives of some β-chain mutant hemoglobins is studied in the temperature range 300–10 K and compared to that of wild-type carbonmonoxy hemoglobin. The band profile at various temperatures is modeled as a Voigt function that accounts for homogeneous broadening and for the coupling with high- and low-frequency vibrational modes, while inhomogeneous broadening is taken into account with a gaussian distribution of purely electronic transition frequencies. The various contributions to the overall bandwidth are singled out With this analysis and their temperature dependence, in turn, gives information on structural and dynamic properties of the system studied. In the wildtype and mutant hemoglobins, the values of homogeneous bandwidth and of the coupling constants to high-frequency vibrational modes are not modified with respect to natural human hemoglobin, thus indicating that the local electronic and vibrational properties of the heme–CO complex are not altered by the recombinant procedures. On the contrary, differences in the protein dynamic behavior are observed. The most relevant are those relative to the “polar isosteric” βVal-67(Ell) →Thr substitution, localized in the heme pocket, which results in decreased coupling with low-frequency modes and increased anharmonic motions. Mutations involving residue βLys-144(HC1) at the C-terminal and residue βCys-112(G14) at the α₁β₁ interface have a smaller effect consisting in an increased coupling with low-frequency modes. Mutations at the β-N-terminal and at the α₁β₂ interface have no effect on the dynamic properties of the heme pocket. © 1995 Wiley-Liss, Inc.     

Hybrid recombinant human leukocyte interferon inhibits differentiation in murine B-16 melanoma cells

We have investigated the effects of recombinant human leukocyte interferons (IFN-alpha A and IFN-alpha D) and various hybrid recombinant human leukocyte interferons on differentiation in B-16 mouse melanoma cells. Inhibition of both spontaneous and melanocyte hormone stimulated differentiation was observed with one hybrid construct, IFN-alpha A/D (Bgl) consisting of amino acids 1 to 62 from IFN-alpha A and amino acids 64 to 166 from IFN-alpha D. In contrast, the parental human interferons, IFN-alpha A and IFN-alpha D, when used alone or in combination, as well as other hybrid human leukocyte interferons, did not cause significant inhibition of melanogenesis in B-16 mouse cells. The tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) also inhibited B-16 differentiation and the combination of TPA with IFN-alpha A/D (Bgl) or mouse L-cell interferon was synergistic in delaying melanogenesis. These studies indicate that the IFN-alpha A/D (Bgl) hybrid that exhibits antiviral activity on mouse cells can also inhibit differentiation of murine cells.     

Inhibition of parathormone-stimulated bone resorption by type I interferon

The effect of Type I interferon on bone resorption was studied by measuring its effect on parathormone-stimulated calcium release from neonatal murine calvaria in vitro. A pure human recombinant leukocyte interferon hybrid of the A and D subtypes was used, which has high antiviral activity on mouse cells. Calcium release was inhibited in a dose dependent fashion with 50% inhibition at about 10(-10) M or 600 U/ml, and the inhibition was reversible. The presence of interferon was required before or during the activation phase of the resorptive response, when the formation of osteoclasts from precursor cells would occur. When added to actively resorbing bone it had no effect. The data suggest that Type I interferon can inhibit the parathormone-regulated development of active osteoclasts, possibly by inhibiting osteoclast precursor differentiation.     

Isolation of restriction enzyme EcoVIII, an isoschizomer of HindIII, produced by Escherichia coli E1585-68

A restriction endonuclease designated EcoVIII, an isoschizomer of HindIII, was isolated from Escherichia coli E1585-68 and purified by dextran-polyethylene glycol (DPG) phase partition, ammonium sulfate precipitation, phospho- and DEAE-cellulose chromatography, and hydroxylapatite chromatography. The purified EcoVIII was stable during the purification procedure and its high specific activity required 10 mM Mg²⁺. Unlike HindIII, Eco VIII exhibited a high specific activity even at low pH (pH 6.3) and showed the highest activity at 48° C. Transformation of purified plasmid DNA from E. coli E1585-68 into K-12 indicated that the EcoVIII gene was carried on a multicopy 4.4-kb miniplasmid. EcoVIII seems to be preferable to HindIII for its production and use because of easier handling of producer cells and a wider range of activity.