Effect of osmotic stress on protein turnover in Lemna minor fronds

Evidence is presented that although many proteins from the fronds of Lemna minor L. undergo enhanced degradation during osmotic stress, ribulose-1,5-bisphosphate carboxylase (RuBPCase) is not degraded. Instead RuBPCase is converted in a series of steps to a very high-molecular-weight form. The first step involves the induction of an oxidase system which after 24 h of stress converts RuBPCase to an acidic and catalytically inactive form. Subsequently, the oxidised RuBPCase protein is gradually polymerized to a number of very large aggregates (molecular weight of several million).The conversion of RuBPCase to a high-molecular-weight form appears to be correlated with (i) a reduction in the number of-SH residues and (ii) the susceptibility to in-vitro proteolysis. Indeed, the number of-SH groups per RuBPCase molecule decreases from 89 in the native enzyme to 54 and 22 in the oxidised and polymerized forms, respectively. On the other hand, the oxidised enzyme is more susceptible to in-vitro proteolysis than the native form. However, it is the polymerized form of RuBPCase which is particularly susceptible to in-vitro proteolysis.Western-blotting experiments and anti-ubiquitin antibodies were used to detect the presence of ubiquitin conjugates in extracts from osmotically stressed Lemna fronds. The possible involvement of ubiquitin in the formation of the aggregates is discussed.Abbreviations DTT dithiothreitol - EDTA ethylenediamine-tetraacetic acid - FPLC fast protein liquid chromatography - kDa kilodaltons - PAGE polyacrylamide gel electrophoresis - PMSF phenylmethylsulphonyl fluoride - RuBPCase ribulose bisphosphate carboxylase - SDS sodium dodecyl sulphate - Tris 2-amino-2-(hydroxymethyl)-1,3-propanediol     

Role of protein and RNA synthesis in the initiation of auxin-mediated growth in coleoptiles of Zea mays L.

The kinetics of inhibition by protein- and RNA-synthesis inhibitors (cycloheximide and cordycepin, respectively) of indole-3-acetic acid (IAA)-induced elongation growth were investigated using abraded coleoptile segments of Zea mays L. Removal of the cuticle — a diffusion barrier for solutes — by mechanical abrasion of the outer epidermal cell wall increased the effectiveness of inhibitors tremendously. In an attempt to elucidate the role of growth-limiting protein(s) (GLP) in the growth mechanism the following results were obtained. The elongation induced by IAA was completely inhibited when cycloheximide (10 mol·l^-1) was applied to abraded coleoptile segments as shortly as 10 min before the onset of the growth response (=5 min after administration of IAA). However, when cycloheximide was applied after 60 min of IAA treatment (when a steady-state growth rate is reached), the time required for complete cessation of growth was much longer (about 40 min). Cycloheximide inhibited the incorporation of [³H]leucine into protein within about 5 min. Cordycepin (400 mol·l^-1) prevented IAA-induced growth when applied as shortly as 25 min before the onset of the growth response (=10 min before administration of IAA) but required more than 60 min for a full inhibition of steady-state growth. The incorporation of [³H]adenosine into RNA was inhibited by cordycepin within 10 min. It is concluded that, contrary to previous investigations with nonabraded organ segments, the initiation of growth by IAA depends directly on the synthesis of GLP. Moreover, the apparent lifetime of GLP is at least four times longer than the time required by cycloheximide to inhibit the initiation of growth by IAA. This is interpreted to mean that GLP is not present before IAA starts to act but is synthesized as a consequence of IAA action starting a few minutes before the initiation of growth. Interpreting the kinetics of growth inhibition by cordycepin in a similar way, we further conclude that GLP synthesis is mediated by IAA-induced synthesis of the corresponding mRNA which starts about 10 min before the onset of GLP synthesis. Inhibition by cycloheximide and cordycepin of IAA-induced growth cannot be alleviated by acidifying the cell wall to pH 4-5, indicating that these inhibitors do not act on growth via an inhibition of auxin-mediated proton excretion.Abbreviations CHI cycloheximide - COR cordycepin - GLP growth-dimiting protein(s) - IAA indole-3-acetic acid - mRNA_GLP mRNA coding for GLP     

The glue protein of ribbed mussels (Geukensia demissa): a natural adhesive with some features of collagen

Summary The Atlantic ribbed musselGeukensia (Modiolus)demissa attaches itself to the roots of cord grass and other hard objects in tidal salt marshes by spinning adhesive byssal threads. The precursor of a protein apparently present in the adhesive plaques of the threads was isolated in quantity from the foot of the mussel. The protein has an apparent molecular weight of 130000, a pI of 8.1, and contains a high proportion of Gly, Glu/Gln, Lys and 3,4-dihydroxyphenyl-l-alanine (DOPA). Sequence of tryptic peptides suggests a pattern of repeated motifs, such as: Gly-DOPA-Lys, and X-Gly-DOPA-Y-Z-Gly-DOPA/Tyr-Lys, where X is Thr or Ala in octapeptides and Gln-Thr in nonapeptides. Y is variable, but more often than not hydrophobic; and Z is frequently Pro or 4-trans-hydroxyproline (Hyp). The presence of Pro-Gly and Hyp-Gly sequences of -hydroxylysine in the protein is reminiscent of typical collagens; however, the protein is not labile to clostridial collagenase, nor does collagen cross-react with antibodies raised against the mussel protein. Unlike typical collagens, Gly probably occurs only at every 4th or 5th residue in this unusual mussel protein.Abbreviations Anti-Gdfp anti-G. demissa foot protein - Dopa 3,4-dihydroxyphenylalanine - CTAB cetyltrimethylammonium bromide - HPLC high performance liquid chromatography - PAGE polyacrylamide gel electrophoresis Supported by grants from the National Science Foundation (DMB 8500301) and the Office of Naval Research (N00014-86K-0717)     

A similar protein portion for two exoglucanases secreted by Saccharomyces cerevisiae

Exoglucanase (exo-1,3-β-D-glucan glycohydrolase, EC 3.2.1.56) activity secreted by Saccharomyces cerevisiae into the culture medium was separated by ion exchange chromatography into two glycoprotein isoenzymes which contributed 10% (exoglucanase I) and 90% (exoglucanase II) towards the total activity. Analysis of the “in vitro” deglycosylated products by polyacrylamide gel electrophoresis under native or denaturing conditions indicated that the protein portions of both exoglucanases exhibited identical mobility, each one consisting of two polypeptides with M _r of 47000 and 48000. The same profile was shown by the exoglucanase secreted in the presence of tunicamycin. Antibodies raised against the protein portion of exoglucanase II did react with both native exoglucanases and their deglycosylated products with a pattern indicative of immunological identity. Digestion of the “in vitro” deglycosylated products of both exoglucanases with Staphylococcus aureus V-8 protease or trypsin generated the same proteolytic fragments in each case. Only exoglucanase II was secreted by protoplasts. These and previously reported results indicate that the protein portions of both isoenzymes may be the product of the same gene (or a family of related genes), and that exoglucanase I is a product of enzyme II, modified by a process occurring beyond the permeability barrier of the cell.     

Protein kinase C inhibition by calmodulin and its fragments

Inhibition of protein kinase C (PKC) by calmodulin is investigated and we describe the localization of inhibitory sequences within the calmodulin molecule. We present evidence that calmodulin inhibits PKC through an inhibition of the activation of PKC associated with lipid membranes: Binding of PKC to lipid vesicles is not affected, but activation is abolished. The potent calmodulin antagonist R24571 (calmidazol) did not affect the inhibition of PKC by calmodulin at concentrations up to 10^–5 M. Two tryptic fragments of calmodulin were isolated which inhibited PKC. They were only slightly less potent than intact calmodulin with an IC₅₀ of 6 µ M compared to 1 µ M of intact calmodulin. They were identified as Ser³⁸-Arg⁷⁴ and His¹⁰⁷-Lys¹⁴⁸. Each of the inhibiting fragments contains an intact Ca²⁺-binding domain with complete helix-loop-helix structure (EF hand). Other calmodulin peptides showed only weak inhibitory activity. Both fragments did not stimulate cAMP phosphodiesterase even at concentrations 100-fold higher than the calmodulin concentration needed for maximal stimulation. None of the fragments acted as a calmodulin antagonist.     

Cellular localization of cytochrome c 553 in the N2-fixing cyanobacterium Anabaena variabilis

The in situ location of the electron carrier protein cytochrome C ₅₅₃ (cyt c ₅₅₃) has been investigated in both vegetative cells and heterocysts of the cyanobacterium Anabaena variabilis ATCC 29413 using the antibody-gold technique, carried out as a post-ernbedding immunoelectron microscopy procedure. When using a rabbit polyclonal anti-cyt c ₅₅₃ specific antiserum an intense labelling, associated mainly with the cell periphery (cytoplasmic membrane and periplasmic area), was seen in both heterocysts and vegetative cells. The selective release of most of the cellular cyt c ₅₅₃ during a Tris-EDTA treatment confirms a periplasmic localization of this protein in A. variabilis. The results indicate that most of cyt c ₅₅₃ is located in the periplasmic space. The roles ascribed to this protein in both respiration and photosynthesis in cyanobacteria are discussed.Abbreviations Cyt c ₅₅₃ cytochrome c ₅₅₃ - PBS phosphate buffered saline (20 mM sodium phosphate, 0.9% NaCl, pH 7.4) - PMSF phenylmethylsulfonyl fluoride Recipient of a Research Fellowship of the Alexander von Humboldt Foundation (Bonn, FRG) for a leave to the University of Konstanz.     

Protein phosphorylation in Streptomyces albus

The phosphorylated proteins of Streptomyces albus, radioactively labeled with [32P]orthophosphate have been analyzed by gel electrophoresis and autoradiography. More than 10 protein species were found to be phosphorylated. With [32P]ATP as substrate cell free extracts phosphorylated endogenous proteins in vitro which were predominantly phosphorylated in vivo. From cell extract which exhibited active phosphorylated in vitro, a protein kinase has been partially purified. The kinase activity was identified in fractions corresponding to a 90 kDa protein.     

Development of mutants of the mosquitocidal bacterium Bacillus thuringiensis subspecies morrisoni (PG-14) toxic to lepidopterous or dipterous insects

The parasporal body of the mosquitocidal isolate (PG-14) of Bacillus thuringiensis subsp. morrisoni (BTM) contains five major proteins with molecular masses of, respectively, 27.3, 65, 128, 135, and 144 kDa. Proteins corresponding in mass to the first four of these also occur in the mosquitocidal strain, B. thuringiensis subsp. israelensis (BTI), and it is thought therefore that the mosquitocidal activity of both strains is due to these four proteins. In other studies it has been shown that each of these proteins exhibits from moderate to high toxicity to mosquitoes, though the specific toxicity of the 144 kDa protein in PG-14 to mosquitoes remains unknown. In the present study, two parasporal body mutants (M146 and M242) of PG-14 were developed growing the wild-type strain at 42 degrees C. The parasporal body of M146 contained less of the 65-kDa protein and was less toxic (LC50 = 108 ng/ml) to mosquitoes than the wild-type strain (LC50 = 8.3 ng/ml). The parasporal body of M242 consisted of a bipyramidal crystal composed of a 144-kDa protein that was not toxic to the mosquito, Aedes aegypti, but exhibited substantial toxicity (LC50 = 2.5 micrograms/ml) to the lepidopteran. Trichoplusia ni. Because the parasporal bodies of BTI and BTM PG-14 are similar in mosquitocidal toxicity on a weight basis, the latter results suggest the 144-kDa protein, though not mosquitocidal alone, can contribute to mosquitocidal, activity when in the presence of other mosquitocidal proteins.     

Maggot therapy: a review of the therapeutic applications of fly larvae in human medicine, especially for treating osteomyelitis

In traditional medical practice, the larvae of some Diptera: Calliphoridae, notably Lucilia illustris (Meigen), L.sericata (Meigen) and Phormia regina (Meigen), have been employed for maggot therapy, i.e. to help clean lesions antiseptically, especially for treatment of chronic osteomyelitis. This mode of treatment remains appropriate for cases where antibiotics are ineffective and surgery impracticable.