Role of strategic cysteine residues in oxidative damage to the yeast plasma membrane H(+)-ATPase caused by Fe- and Cu-containing Fenton reagents

Damage caused to Saccharomyces cerevisiae SY4 plasma membrane H(+)-ATPase by Fe- and Cu-Fenton reagents was determined in secretory vesicles containing enzyme in which Cys residues were replaced singly or in pairs by Ala. Cys-221 situated in a beta-sheet domain between M2 and M3 segments, phosphorylation domain-located Cys-409 and Cys-532 situated at the ATP-binding site play a role in the inactivation. In the presence of all three residues the enzyme exhibited a certain basic inactivation, which did not change when Cys-532 was replaced with Ala. In mutants having intact Cys-532 but lacking one or both other cysteines, replacement of Cys-221 with Ala led to lower inactivation, suggesting that Cys-221 may serve as a target for metal-catalyzed oxidation and intact Cys-532 promotes this target role of Cys-221. In contrast, the absence of Cys-409 caused higher inactivation by Fe-Fenton. Cys-532 thus seems to serve as a target for Fe-Fenton, intact Cys-409 causing a conformational change that makes Cys-532 less accessible to oxidation. The mutant lacking both Cys-221 and Cys-409 is more sensitive to Fe-Fenton than to Cu-Fenton and the absence of both Cys residues thus seems to expose presumable extra Fe-binding sites. These data and those on protection by ATP, ADP, 1,4-dithiothreitol and deferrioxamine B point to complex interactions between individual parts of the enzyme molecule that determine its sensitivity towards Fenton reagents. ATPase fragmentation caused by the two reagents differed in that the Fe-Fenton reagent produced in Western blot "smears" whereas the Cu-Fenton reagent produced defined fragments.

Viability and formation of conjugated dienes in plasma membrane lipids of Saccharomyces cerevisiae, Schizosaccharomyces pombe, Rhodotorula glutinis and Candida albicans exposed to hydrophilic, amphiphilic and hydrophobic pro-oxidants

Effects of four lipid peroxidation-inducing pro-oxidants--amphiphilic tert-butyl hydroperoxide (TBHP), hydrophobic 1,1'-azobis(4-cyclohexanecarbonitrile) (ACHN), hydrophilic FeII and 2,2'-azobis(2-amidinopropane)dihydrochloride (AAPH)--on cell growth and on generation of peroxidation products in isolated plasma membrane lipids were determined in four yeast species (S. cerevisiae, S. pombe, R. glutinis and C. albicans) differing in their plasma membrane lipid composition. TBHP and ACHN inhibited cell growth most strongly, FeII and AAPH exerted inhibitory action for about 2 h, with subsequent cell growth resumption. S. cerevisiae strain SP4 was doped during growth with unsaturated linoleic (18:2) and linolenic (18:3) acids to change its resistance to lipid peroxidation. Its plasma membranes then contained some 30% of these acids as compared with some 1.3% of 18:2 acid found in undoped S. cerevisiae, while the content of (16:1) and (18:1) acids was lower than in undoped S. cerevisiae. The presence of linoleic and linolenic acids in S. cerevisiae cells lowered cell survival and increased the sensitivity to pro-oxidants. Peroxidation-generated conjugated dienes (CD) were measured in pure TBHP- and ACHN-exposed fatty acids used as standards. The CD level depended on the extent of unsaturation and the pro-oxidant used. The TBHP-induced CD production in a mixture of oleic acid and its ester was somewhat lower than in free acid and ester alone. In lipids isolated from the yeast plasma membranes, the CD production was time-dependent and decreased after a 5-15-min pro-oxidant exposure. ACHN was less active than TBHP. The most oxidizable were lipids from S. cerevisiae plasma membranes doped with linoleic and linolenic acids and from C. albicans with indigenous linolenic acid.

ATP-dependent proteinases in bacteria

Cytoplasmic proteolysis is an indispensable process for proper function of a cell. Degradation of many intracellular proteins is initiated by ATP-dependent proteinases, which are involved in the regulation of the level of proteins with short half-lives. In addition, they remove many damaged and abnormal proteins and thus play also an important role during stress. ATP-dependent proteinases are large multi-subunit assemblies composed of proteolytic core domains and ATPase-containing regulatory domains on a single polypeptide chain or on distinct subunits, which can act as molecular chaperones. This review briefly summarizes the data about four main groups of these proteinases in bacteria (i.e. Lon, Clp family, HslUV and FtsH) and characterizes their structure, mechanism of action and properties.

Differences in the regulation of the intracellular Ca2+-dependent serine proteinase activity between Bacillus subtilis and B. megaterium

A rise of the intracellular serine proteinase activity (ISP) during postexponential growth of Bacillus subtilis was decreased by a temperature upshift from 35 degrees to 42 degrees C. However, the amount of both molecular forms of the major intracellular serine proteinase ISP1 determined by immunoblotting was similar at both temperatures or even slightly increased at 42 degrees C. The evolution of the ISP activity in B. megaterium showed an opposite temperature dependence, being faster during growth at 42 degrees C. The amount of immunologically detected ISP1 again did not correlate well with the enzyme activity. Moreover, most of the ISP1 molecules in cell-free extracts from B. megaterium were inactive and were activated by increasing the CaCl2 concentration up to 30 mM--unlike B. subtilis, where the enzymic activity was unaffected by Ca2+ concentration. These data suggest that the ISP1 activity in the two bacillar species during postexponential growth is regulated posttranscriptionally, but that the regulatory mechanisms differ.

Effect of pH on proteinase secretion by transformed fibroblast populations

Effect of pH on secretion of proteolytic enzymes in cell cultures of three clonal lines of transformed fibroblasts (K2, T15 and K4) was studied by using 14C-labelled denatured proteins as substrate. One line of malignant macrophages derived from mouse reticulum cell sarcoma (J774.1) was used for comparison. The relative motility index of all cell lines was derived by computer analysis of quantitative estimations of cell dispersion in single-cell-derived colonies. Cultivation at pH 6.5 decreased the growth rate in most experiments as compared with that at pH 7.4, and stimulated cell motility to a different extent. The population of mouse malignant macrophages produced several-fold higher extracellular proteolytic activity than the fibroblast lines. Secretion of proteinases by the malignant macrophages was significantly stimulated by the lower pH. Enzyme secretion by two of the three fibroblast derivatives was also stimulated by acidic pH but to a lesser extent than the secretion of the malignant macrophages. The assessment of motility done by measurement of dispersion of cells in colony proved a positive correlation between motility and proteinase secretion in J774.1 cells and one transformed fibroblast clone (T15) but not in the two other clonal lines.

Activation of the intracellular Ca(2+)-dependent serine protease ISP1 of bacillus megaterium by purification or by high Ca2+ concentrations

The total proteolytic activity of ISP1 determined after its partial purification by size exclusion HPLC increased 3.0, 7.3 and 27.3 times in sporulating, growing and netropsin-treated cells, respectively, as compared with the corresponding original activity in crude cytoplasmic preparations at the same CaCl2 concentration of 3 mM. A similar rise in proteolytic activity occurred on increasing the Ca2+ concentration in the crude cytoplasm from 3 to 30 mM. This activation in the cytoplasm of netropsin-treated and sporulating cells was not reversed by subsequent lowering of CaCl2 concentration back to 3 mM by dialysis. Moreover, a similar activation appeared even after the same dialysis of cytoplasm that had not been exposed to 30 mM CaCl2. The activation was probably due to the processing of ISP1, as established by SDS-PAGE and immunoblotting, but an involvement of additional regulation factor(s), e.g. an inhibitor or other molecules, is possible.

Heat and osmotic stress enhance the development of cytoplasmic serine proteinase activity in sporulating Bacillus megaterium

The intracellular Ca(2+)-dependent serine proteinase (ISP1) activity in the cytoplasm of nongrowing Bacillus megaterium incubated in a sporulation medium was determined at 35 degrees C and at temperatures decreasing the sporulation frequency (42 degrees C) or suppressing sporulation (43.5 degrees C). The enzyme in the crude cytoplasmic fraction was partially inhibited by a loosely bound inhibitor(s) because the ISP1 activity rose after protein fractionation by HPLC. Temperature shift-up or osmotic stress applied at 35 degrees C increased the development of the ISP1 activity several times. The increase was caused at least partially by the synthesis of the enzyme protein, as proved by SDS-PAGE and immunoblotting of the cytoplasm. This enzyme thus probably belongs among heat-shock proteins.

Two microassays for determination of a wide range of proteolytic activities using Azocoll as substrate

Two micromethods for measuring proteolytic activity were developed. A semiquantitative assay on microtitre plates with granular Azocoll as substrate is based on the determination of the time of first appearance of pink colour, t, in the reaction mixture and proteolytic activity is expressed as 1/t. This simple, sensitive and economical method is convenient for preliminary testing of a large number of small samples with unknown proteolytic activity, such as fractions after chromatography. It speeds up considerably proteinase purification. The other test, a quantitative microassay, is a low-cost and time-saving version of the classical method which reduces material consumption and includes automated measurement of absorbance in microtitre plates by a Multiscan reader. Application of these methods are demonstrated.

Effect of actinomycin D on viability, sporulation and nucleotide pool of Bacillus megaterium

A transient 7-fold rise of ppGpp concentration, 2-3-fold increase of pppGpp concentration and 50% drop of the concentration of GTP in Bacillus megaterium cells immediately after their transfer to the sporulation medium were observed. Actinomycin D, in concentrations inhibiting RNA synthesis by 95%, blocked the rise of the (p)ppGpp pool and caused an instant several-fold increase of the GTP level. When the cells were exposed to actinomycin D in the sporulation medium for a 1-h period (time 0-1 h, 1-2 h or 2.20-3.20-h), they were able to form colonies on nutrient agar after being kept, in addition for 1-2 h in the sporulation medium free of the antibiotic. The ability of sporulation was, however, markedly limited. The share of cells that could sporulate increased when the irreversible sporulation phase was reached.

Mutants of Bacillus megaterium with altered synthesis of an exocellular neutral proteinase

Germinated spores of Bacillus megaterium were mutagenized with ethyl methanesulphonate and spread on test agar with caseinate. Colonies with altered proteolytic zones or morphology were isolated and tested in liquid media. The mutants can be divided into four groups: A) those producing more proteinase in both growth and sporulation media, B) those producing the same amount of the enzyme in growth medium but higher amount in sporulation medium, C) those producing less proteinase in the growth medium and more in the sporulation one, D) those producing less or no enzyme. Clones of the first three groups were phenotypically asporogenic. All mutants producing more enzyme during growth retained their sensitivity to repression by amino acids. Isolation of mutants of types B) and C) supports the idea of differences in the control of proteinase synthesis during growth and during sporulation.