Caspase-mediated cleavage of JNK during stress-induced apoptosis

The c-Jun N-terminal kinases (JNKs) are a subfamily of the mitogen-activated protein kinases (MAPKs). The JNKs are encoded by three separate genes (jnk1, jnk2, and jnk3), which are spliced alternatively to create 10 JNK isoforms that are either p46 or p54 in size. In this study, we found that the p52 form of JNK emerged in human leukemia MOLT-4 or U937 cells following X-irradiation or heat treatment. The accumulation of p52 coincided with the reduction of p54 JNK. On the other hand, the amounts of p46 JNK did not change by X-irradiation. Induction of the p52 form of JNK also paralleled the appearance of the active form of caspase-3 and was suppressed by a caspase-specific inhibitor, Ac-DEVD-CHO, but not by Ac-YVAD-CHO. In vitro cleavage assays indicated that recombinant human JNK1beta2 and JNK2beta2 were cleaved by caspase-3, and that the mutation of aspartic acid at position 413 of JNK1beta2 or 410 of JNK2beta2 to alanine abolished the cleavage. Altogether, our results demonstrated that p54 JNKs, at least JNK1beta2 and JNK2beta2, were new selective targets of caspases in JNK splicing variants, and suggested that the p52 form could serve as a marker of apoptosis.     

Amphotericin B resistance is recessive in Chinese hamster hybrid cells

Previous studies from our laboratory have shown that Chinese hamster V79 cells mutated to high level resistance to amphotericin B have a lower cellular level of cholesterol, the target molecule for the polyene antibiotic. Two amphotericin B-resistant (AMB^R) mutants were each hybridized to their parental amphotericin B-sensitive (AMB^S) V79 cells. All the hybrids derived from AMB^R/AMB^S fusions were as sensitive to polyene antibiotics (amphotericin B, filipin, and pimaricin) as AMB^S/AMB^S hybrids. The AMB^R/AMB^S hybrids were found to contain cholesterol per phospholipids that is comparable to those in AMB^S or AMB^S/AMB^S. The analysis of hybrids formed between mutant and wild-type cells thus indicated that resistance to amphotericin B is a recessive marker, and that the cellular level of cholesterol is compensated in the AMB^S/AMB^R hybrids. Hybrids of AMB^R and AMB^R cells were all resistant, so that the three AMB^R mutants all fell into a single complementation group.     

Peptide Bond Synthesis by a Mechanism Involving an Enzymatic Reaction and a Subsequent Chemical Reaction

We recently reported that an amide bond is unexpectedly formed by an acyl-CoA synthetase (which catalyzes the formation of a carbon-sulfur bond) when a suitable acid and l-cysteine are used as substrates. DltA, which is homologous to the adenylation domain of nonribosomal peptide synthetase, belongs to the same superfamily of adenylate-forming enzymes, which includes many kinds of enzymes, including the acyl-CoA synthetases. Here, we demonstrate that DltA synthesizes not only N-(d-alanyl)-l-cysteine (a dipeptide) but also various oligopeptides. We propose that this enzyme catalyzes peptide synthesis by the following unprecedented mechanism: (i) the formation of S-acyl-l-cysteine as an intermediate via its “enzymatic activity” and (ii) subsequent “chemical” S → N acyl transfer in the intermediate, resulting in peptide formation. Step ii is identical to the corresponding reaction in native chemical ligation, a method of chemical peptide synthesis, whereas step i is not. To the best of our knowledge, our discovery of this peptide synthesis mechanism involving an enzymatic reaction and a subsequent chemical reaction is the first such one to be reported. This new process yields peptides without the use of a thioesterified fragment, which is required in native chemical ligation. Together with these findings, the same mechanism-dependent formation of N-acyl compounds by other members of the above-mentioned superfamily demonstrated that all members most likely form peptide/amide compounds by using this novel mechanism. Each member enzyme acts on a specific substrate; thus, not only the corresponding peptides but also new types of amide compounds can be formed.     

Growth Inhibition and Appearance of the Membranous Structure in Escherichia coli Infected with Bacteriophage fd

Thirty-six mutants of fd, a virus that infects but does not kill Escherichia coli, were isolated; 35 mutants were categorized into six complementation groups. Abortive infection with mutants in genes 1, 3, 4, 5, and 6, but not in gene 2, produced a cessation of host cell growth, generally linked to low burst size and to the formation of aberrant intracytoplasmic membranous structures. The membranous structure was studied during infection with various phage and hosts. Appearance of the membranous structure was linked specifically to incomplete phage maturation at the cell membrane, rather than solely to the inhibition of host cell growth or to infection with mutant phage, since (i) in one host, cell growth was inhibited, but no membranous structure developed; and (ii) when antibody against virus was added to cells infected with wild-type phage, phage extrusion was inhibited, cell growth stopped, and the membranous structure once again developed.     

In vitro immunomodulating effect of protein-bound polysaccharide,PSK on peripheral blood,regional nodes,and spleen lymphocytes in patients with gastric cancer

Summary PSK, a protein-bound polysaccharide, has been widely used for cancer immunotherapy in Japan. However, the mechanism of its immunomodulatory effect has not been fully clarified. In the present study the in vitro effect of PSK on the lymphocytes of patients with gastric cancer was studied. Culturing lymphocytes with PSK at 5–100 µg/ml increased the level of DNA synthesis, and augmented the cytotoxicities against K562 and KATO-3. Flow-cytometric analysis also showed an increase in the proportion of interleukin-2 (IL-2)-receptor-positive cells after the lymphocytes were cultured with PSK. However the cytotoxicity of cells cultured with PSK was not augmented by the addition of recombinant interferon (rIFN) and rIL-2. Further experiments using fractionated PSK showed that its biological action is present mainly in fractions having molecular masses >10⁵Da. However, these immunomodulations were not seen in all patients. These results suggest that the susceptibility of lymphocytes to PSK may be different in each patients, and that the immunomodulation by PSK may be mediated by mechanisms independent of IFN and IL-2.     

Nitrilase-catalyzed production ofp-aminobenzoic acid fromp-aminobenzonitrile withRhodococcus rhodochrous J1

Summary The reaction conditions for the enzymatic production ofp-aminobenzoic acid were optimized, using a nitrilase in cells ofRhodococcus rhodochrous J1. The highest accumulation, 110 gp-aminobenzoic acid/liter of reaction mixture, was attained fromp-aminobenzonitrile, with a conversion yield of 100%.     

Site-directed mutagenesis for cysteine residues of cobalt-containing nitrile hydratase

Three cysteine residues, which are completely conserved among alpha-subunits in all nitrile hydratases, are thought to be the ligands of a metal ion in the catalytic center of this enzyme. These cysteine residues (i.e. alpha C102, alpha C105 and alpha C107) in the high-molecular-mass nitrile hydratase (H-NHase) of Rhodococcus rhodochrous J1 were replaced with alanine by site-directed mutagenesis using the R. rhodochrous ATCC12674 host-vector system, and the resultant transformants were investigated. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) for the cell-free extracts of each mutant transformant revealed that four mutant transformants (i.e. alpha C105A, alpha C107A, alpha C102A/C105A and alpha C105A/C107A) showed predominant alpha- and beta-subunit protein bands with a mobility identical to those of the native H-NHase, while three mutant transformants (i.e. alpha C102A, alpha C102A/C107A and alpha C102A/C105A/C107A) did not produce the corresponding proteins. The purified former four mutant enzymes showed neither enzymatic activity nor the maximum absorption at 410 nm which was detected in the wild type H-NHase. They also did not contain cobalt ions. Based upon these findings, these three cysteine residues were found to be essential for the active expression of H-NHase.     

Purification and characterization of a novel enzyme, L-threo-3-hydroxyaspartate dehydratase, from Pseudomonas sp. T62

L-threo-3-Hydroxyaspartate dehydratase (L-threo-3-hydroxyaspartate hydro-lyase), which exhibited specificity for L-threo-3-hydroxyaspartate (K(m)=0.74 mM, V(max)=37.5 micromol min(-1) (mg protein)(-1)) but not for D-threo or D, L-erythro-3-hydroxyaspartate, was purified from a cell-free extract of Pseudomonas sp. T62. The activity of the enzyme was inhibited by hydroxylamine and EDTA, which suggests that pyridoxal 5'-phosphate and divalent cations participate in the enzyme reaction. The NH(2)-terminal amino acid sequence showed significant similarity to the Saccharomyces cerevisiae YKL218c gene product, a hypothetical threonine dehydratase. However, the purified enzyme showed no threonine dehydratase activity.     

Functional analyses and application of microbial lactonohydrolases

Microbial lactonohydrolases (intramolecular ester bond-hydrolyzing enzymes) with unique properties were found. The lactonohydrolase fromFusarium oxysporum catalyzes enantioselective hydrolysis of aldonate lactones andd-pantoyl lactone (d-PL). This enzyme is useful for the large-scale optical resolution of racemic PL. TheAgrobacterium tumefaciens enzyme catalyzes asymmetric hydrolysis of PL, but the stereospecificity is opposite to that of theFusarium enzyme. Dihydrocoumarin hydrolase (DHase) fromAcinetobacter calcoaceticus is a bifunctional enzyme, which catalyzes not only hydrolysis of aromatic lactones but also bromination of monochlorodimedon in the presence of H₂O₂ and dihydrocoumarin. DHase also hydrolyzes several linear esters, and is useful for enantioselective hydrolysis of methyldl-β-acetylthioisobutyrate and regioselective hydrolysis of methyl cetraxate.