Classification of phospholipases A2 according to sequence. Evolutionary and pharmacological implications

The inhibition of elongation of Bacillus megaterium KM growing in the presence of low concentrations of nocardicin A resulted in the production of osmotically stable, actively dividing coccal-shaped cells. Saturation of penicillin-binding proteins 3a and 3b with nocardicin A in vivo at these concentrations was correlated with the inhibition of cell elongation. Analysis of the DD-carboxypeptidase activity of isolated vegetative membranes of B. megaterium KM in vitro indicated that penicillin-binding protein 4 is not a DD-carboxypeptidase under the assay conditions used. Penicillin-binding proteins were analysed by two-dimensional gel electrophoresis and the suitability of lysozyme treatment of cells as a method of membrane preparation was investigated with regard to the detection of proteins with highly labile penicillin-binding activities in vitro.     

Differential fluorescence labelling with 5-dimethyl-aminonaphthalene-1-sulfonyl chloride of intact cells and isolated membranes in Salmonella typhimurium and Acholeplasma laidlawii

For fluorescence labelling intact cells and isolated cell envelopes (membranes) from Salmonella typhimurium and Acholeplasma laidlawii were treated with mixed dansylchloride-lecithin-cholesterol vesicles. This kind of dansylation, which has been supposed to be specific for cell surface proteins, produced fluorescent protein pattern after SDS-polyacrylamide gel electrophoresis only when isolated envelopes were dansylated. Acid hydrolysis of fluorescent cell envelopes of Salmonella typhimurium yielded O-dansyltryosine and epsilon-N-dansyl-lysine besides the free sulfonic acid and unidentified compounds. However, no fluorescent proteins were detectable in cell envelopes isolated from dansylated intact bacteria from Salmonella typhimurium. In accord Acholeplasma laidlawii showed only fluorescence from proteins with a molecular weight higher than 100000.     

Purification and characterization of the penicillin-binding protein that is the lethal target of penicillin in Bacillus megaterium and Bacillus licheniformis. Protein exchange and complex stability.

The penicillin-binding protein that is thought to be the lethal target of penicillin in Bacillus megaterium (protein 1) has been purified to greater than 95% homogeneity. The membrane-bound penicillin-binding proteins were solubilized with a non-ionic detergent and partially separated from each other by ion-exchange chromatography on DEAE-Sepharose CL-6B. Protein 1 was subsequently purified by covalent affinity chromatography on ampicillin-affinose. Bacillus licheniformis contains an equivalent penicillin-binding protein (protein 1) that can be more readily purified to virtual homogeneity in a one-step procedure. It was separated from the other penicillin-binding proteins by utilizing the observation that in this organism, this particular protein is the only one whose covalent complex with benzylpenicillin subsequently breaks down. Membranes were treated with saturating concentrations of benzylpenicillin followed by the removal of free penicillin and further incubation to allow the complex between benzylpenicillin and protein 1 to break down. The penicillin-binding proteins were then solubilized and applied to a column of ampicillin-affinose to which only protein 1 was bound as the other penicillin-binding proteins still had benzylpenicillin bound to them. Pure protein 1 was eluted from the affinity resin with hydroxylamine. The interaction of benzylpenicillin with purified protein 1 has been studied by separating unbound antibiotic from the benzylpenicillin . protein complex by paper electrophoresis. Benzylpenicillin reacts with the protein rapidly to form a covalent complex and the fully saturated complex has a molar ratio of bound [14C] benzylpenicillin: protein of 0.7:1. The complex breaks down, obeying first-order kinetics, with a half-life of 16 min at 35 degrees C, a value identical to that obtained with the membrane-bound protein. The concentration of benzylpenicillin that results in the formation of 50% of the maximum amount of benzylpenicillin . protein complex is that at which the molar amount of benzylpenicillin present is equal to 50% of the molar amount of penicillin-binding protein, rather than being a measure of any of the kinetic parameters of the binding reaction. This observation may be significant in the interpretation of previous results where the amounts of penicillins needed to kill cells or to inhibit penicillin-sensitive reactions have been expressed as concentrations. The possible importance of the breakdown of beta-lactam . protein complexes in the clinical use of these antibiotics is discussed.     

Identification of tyrosine-phosphorylated proteins associated with the nuclear envelope.

The nuclear envelope separates the nucleoplasm from the rest of the cell. Throughout the cell cycle, its structural integrity is controlled by reversible protein phosphorylation. Whereas its phosphorylation-dependent disassembly during mitosis is well characterized, little is known about phosphorylation events at this structure during interphase. The few characterized examples cover protein phosphorylation at serine and threonine residues, but not tyrosine phosphorylation at the nuclear envelope. Here, we demonstrate that tyrosine phosphorylation and dephosphorylation occur at the nuclear envelope of intact Neuro2a mouse neuroblastoma cells. Tyrosine kinase and phosphatase activities remain associated with purified nuclear envelopes. A similar pattern of tyrosine-phosphorylated nuclear envelope proteins suggests that the same tyrosine kinases act at the nuclear envelope of intact cells and at the purified nuclear envelope. We have also identified eight tyrosine-phosphorylated nuclear envelope proteins by 2D BAC/SDS/PAGE, immunoblotting with phosphotyrosine-specific antibodies, tryptic in-gel digestion, and MS analysis of tryptic peptides. These proteins are the lamina proteins lamin A, lamin B1, and lamin B2, the inner nuclear membrane protein LAP2beta, the heat shock protein hsc70, and the DNA/RNA-binding proteins PSF, hypothetical 16-kDa protein, and NonO, which copurify with the nuclear envelope.     

Specific location of penicillin-binding proteins within the cell envelope of Escherichia coli.

This communication deals with the location of penicillin-binding proteins in the cell envelope of Escherichia coli. For this purpose, bacterial cells have been broken by various procedures and their envelopes have been fractioned. To do so, inner (cytoplasmic) and outer membranes were separated by isopycnic centrifugation in sucrose gradients. Some separation methods (Osborn et al., J. Biol. Chem. 247:3962-3972, 1972; J. Smit, Y. Kamio, and H. Nikaido, J. Bacteriol. 124:942-958, 1975) revealed that penicillin-binding proteins are not exclusively located in the inner membrane. They are also found in the outer membrane (A. Rodríguez-Tébar, J. A. Barbas, and D. Vásquez, J. Bacteriol. 161:243-248, 1985). Under the milder conditions for cell rupture used in this work, an intermembrane fraction, sedimenting between the inner and outer membrane, can be recovered from the gradients. This fraction has a high content of both penicillin-binding proteins and phospholipase B activity and may correspond to the intermembrane adhesion sites (M. H. Bayer, G. P. Costello, and M. E. Bayer, J. Bacteriol. 149:758-769, 1982). We postulate that this intermembrane fraction is a labile structure that contains a high amount of all penicillin-binding proteins which are usually found in both the inner and outer membranes when the adhesion sites are destroyed by the cell breakage and fractionation procedures.     

Supersensitivity of Escherichia coli Cells to Several β-Lactam Antibiotics Caused by Rod− Morphology Mutations at the mrd Gene Cluster

Two kinds of spherical mutants, mrdA and mrdB mutants, have been isolated from Escherichia coli strain K12. The mrdA mutants have thermosensitive penicillin-binding protein 2, while the mrdB mutants have normal penicillin-binding proteins. Both kinds of mutants form spherical cells at 42°C and are resistant to the amidinopenicillin, mecillinam, at the same temperature. The two mutations have been mapped very close to lip at 14.2 min (revised chromosome linkage map, 1980) on the E. coli chromosome. Both mutations cause supersensitivities of cell growth to various β-lactam antibiotics, such as ampicillin, cephalexin, cefoxitin and nocardicin A at 42°C.     

Fractionation of the Providencia stuartii cell envelope

Cell envelopes (i.e. unfractionated inner and outer membranes) were obtained from Providencia stuartii by following procedures previously applied to the isolation of envelopes from Escherichia coli. The P. stuartii envelopes contained known inner membrane enzymes that included a variety of dehydrogenases and ATPase. The catalytic activity of the ATPase depended upon the concentration of magnesium ions, the substrate (ATP) level and the ratio of magnesium ions to ATP. Cell envelopes from P. stuartii were further fractionated to recover inner and outer membrane polypeptides by treatment with the detergent Sarkosyl. Proteins from the periplasmic region were recovered by a simple osmotic shock procedure also previously applied to E. coli. The purity of the various P. stuartii cell envelope fractions was assessed by a combination of techniques that included one- and two-dimensional gel electrophoresis of proteins, enzyme assays and detection of penicillin-binding proteins.     

Dynamic associations of heterochromatin protein 1 with the nuclear envelope

To study the dynamics of mammalian HP1 proteins we have microinjected recombinant forms of mHP1alpha, M31 and M32 into the cytoplasm of living cells. As could be expected from previous studies, the three fusion proteins were efficiently transported into the nucleus and targeted specific chromatin areas. However, before incorporation into these areas the exogenous proteins accumulated in a peripheral zone and associated closely with the nuclear envelope. This transient association did not occur when the cells were treated with deacetylase inhibitors, indicating an acetylation-inhibited interaction. In line with these observations, recombinant HP1 proteins exhibited saturable binding to purified nuclear envelopes and stained the nuclei of detergent-permeabilized cells in a rim-like fashion. Competition experiments with various M31 mutants allowed mapping of the nuclear envelope-binding site within an N-terminal region that includes the chromodomain. A His(6)-tagged peptide representing this region inhibited recruitment of LAP2beta and B-type lamins around the surfaces of condensed chromosomes, suggesting involvement of HP1 proteins in nuclear envelope reassembly.     

Electron Microscopic Observations on the Structure of the Envelopes of Mature Elementary Bodies and Developmental Reticulate Forms of Chlamydia psittaci

Purified suspensions of Chlamydia psittaci were prepared from L cells. Thin sections of intact elementary bodies and intact developmental reticulate bodies and of their purified envelopes were observed by electron microscopy. In both intact organisms and partially purified envelopes, two membranous structures, each appearing in electron micrographs as two darkly stained layers, were observed. In the elementary body sections, the outer membrane was round, apparently rigid, and was not soluble in 0.5% sodium dodecyl sulfate. The inner layer was irregular in shape and was completely removed by detergent treatment. We interpret these results to indicate that the outer rigid layer of the envelope is the cell wall and the inner layer is the cytoplasmic membrane. When the fragile reticulate body envelopes were similarly studied, the outer cell wall was clearly visible, and some evidence of an inner membrane was seen. After treatment with nucleases and detergent, all evidence of inner or cytoplasmic membrane was removed, but the outer cell wall remained. Thus, it appears that the cell wall of this organism is continuous throughout the growth cycle and that the fragility and lack of rigidity of the reticulate body cell is due to changes in chemical composition or structure of the cell wall.     

Effects of nonionic, ionic, and dipolar ionic detergents and EDTA on the Brucella cell envelope

Cell envelopes prepared from smooth and rough strains of Brucella were characterized on the basis of lipopolysaccharide and protein content. The action of three kinds of detergents on Brucella cell envelopes and Escherichia coli control cell envelopes was examined on the basis of the proteins and lipopolysaccharides that were extracted. As compared with those of E. coli, Brucella cell envelopes were resistant to nonionic detergents. Zwittergents 312 and 316 were most effective in extracting E. coli cell envelopes, and Zwittergent 316 was most effective in extracting Brucella cell envelopes. Sarkosyl extracted proteins but extracted only trace amounts of lipopolysaccharides from cell envelopes of both bacteria. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis of the Sarkosyl-resistant proteins revealed a composition similar to that of the proteins exposed on the surfaces of viable cells, as determined by the lactoperoxidase-125I radioiodination method. EDTA, with either Tris-HCl or Tris-HCl-Triton X-100, did not have detectable effects on Brucella cell envelopes. Ultracentrifugation of purified lipopolysaccharides in detergents and EDTA demonstrate that, in contrast to that of E. coli, Brucella lipopolysaccharide was not stabilized by divalent cations. Sarkosyl was ineffective in dispersing lipopolysaccharides, whereas the action of Zwittergents was related to the length of their alkyl chains.     

Penicillin-binding proteins of pathogenic Escherichia coli strains

The penicillin-binding proteins of 11 pathogenic Escherichia coli strains, including enteropathogenic, enterotoxigenic, enteroinvasive, enteroaggregative, and enterohemorrhagic E. coli, were detected in gels following the labeling of isolated cell envelopes with [³H]benzylpenicillin. The electrophoretic profiles, sensitivities to and morphological changes induced by β-lactam antibiotics showed that the penicillin-binding proteins of most pathogenic E. coli possess structural and physiological functions similar to those of E. coli K12.     

Epidermal proteins of cultured human and bovine keratinocytes.

Bovine and human epidermal cells were cultured on mitomycin C treated fibroblasts. The cells were carried through four passages and found to synthesize fibrous proteins and insoluble cell envelopes. Acid buffer soluble fibrous protein, prekeratin, and urea soluble fibrous protein were both identified and the latter was the major component in older cultures. Some of the prekeratin polypeptides of intact tissue were not found in cultured cells, but the ones that were present corresponded to those of whole tissue. X-ray diffraction, amino acid analysis and immunological techniques were used to establish that the polypeptides were keratins. The insoluble cell envelopes had a higher proline and 1/2 cystine content than the fibrous protein, similar to what is found in whole epidermis. Histidase, a characteristic enzyme marker of whole epidermis, was not observed in cultured cells. These studies indicate that differentiation occurs in cultured cells but it may not be as complete as in intact tissue.     

Staphylococcus aureus and Micrococcus luteus peptidoglycan transglycosylases that are not penicillin-binding proteins.

Major peptidoglycan transglycosylase activities, which synthesize uncross-linked peptidoglycan from lipid-linked precursors, were solubilized from the membranes of Staphylococcus aureus and Micrococcus luteus and were partially purified. The transglycosylase activities were separated from penicillin-binding proteins by solubilization and by purification steps. Therefore, we concluded that these activities were not activities of the penicillin-binding proteins, which are the presumptive peptidoglycan transpeptidases in these gram-positive cocci. Unlike Escherichia coli, in which the network structure of peptidoglycan is synthesized by multiple two-headed penicillin-binding proteins with both transpeptidase and transglycosylase activities, these gram-positive cocci have cell wall peptidoglycan which seems to be synthesized by penicillin-binding protein transpeptidases and a separate transglycosylase.     

The nucleotide sequences of the ponA and ponB genes encoding penicillin-binding protein 1A and 1B of Escherichia coli K12

Penicillin-binding proteins 1A and 1B of Escherichia coli are the major peptidoglycan transglycosylase-transpeptidases that catalyse the polymerisation and insertion of peptidoglycan precursors into the bacterial cell wall during cell elongation. The nucleotide sequence of a 2764-base-pair fragment of DNA that contained the ponA gene, encoding penicillin-binding protein 1A, was determined. The sequence predicted that penicillin-binding protein 1A had a relative molecular mass of 93 500 (850 amino acids). The amino-terminus of the protein had the features of a signal peptide but it is not known if this peptide is removed during insertion of the protein into the cytoplasmic membrane. The nucleotide sequence of a 2758-base-pair fragment of DNA that contained the ponB gene, encoding penicillin-binding protein 1B, was also determined. Penicillin-binding protein 1B consists of two major components which were shown to result from the use of alternative sites for the initiation of translation. The large and small forms of penicillin-binding protein 1B were predicted to have relative molecular masses of 94 100 and 88 800 (844 and 799 amino acids). The amino acid sequences of penicillin-binding proteins 1A and 1B could be aligned if two large gaps were introduced into the latter sequence and the two proteins then showed about 30% identity. The amino acid sequences of the proteins showed no extensive similarity to the sequences of penicillin-binding proteins 3 or 5, or to the class A or class C beta-lactamases. Two short regions of amino acid similarity were, however, found between penicillin-binding proteins 1A and 1B and the other penicillin-binding proteins and beta-lactamases. One of these included the predicted active-site serine residue which was located towards the middle of the sequences of penicillin-binding proteins 1A, 1B and 3, within the conserved sequence Gly-Ser-Xaa-Xaa-Lys-Pro. The other region was 19-40 residues to the amino-terminal side of the active-site serine and may be part of a conserved penicillin-binding site in these proteins.     

Interactions of cytoskeletal elements with the plasma membrane of Sarcoma 180 ascites tumor cells

The association of cytoskeletal proteins with cell surface envelopes from Sarcoma 180 ascites cells has been studied by several techniques previously used successfully in studying the interaction of spectrin with erythrocyte membranes. By electron microscopy the envelopes exhibit irregular exterior surfaces and the presence of substantial amounts of “fuzz” at the interior surface. Extraction of the envelopes at low ionic strength and alkaline pH fragments the membranes and depletes them of the “fuzz” with concomitant elution of four major polypeptides of mol. wt >300 000 (Band E), 250 000, 100 000 and 43 000 D. The last three of these have been tentatively identified as actin-binding protein (ABP), α-actinin and actin. Membrane-associated myosin is not eluted under these conditions. Neither actin nor myosin is eluted under conditions commonly used to depolymerize them. However, myosin can be eluted at high salt concentrations if the envelopes have been previously extracted and fragmented with alkaline buffer as above. Extraction of the envelopes with Triton X-100 removes 60% of the membrane lipid and 70–80% of lactoperoxidase-iodinated cell surface proteins without removal of significant amounts of the cytoskeletal proteins. The Triton residues maintain the shape of the original envelopes but have lost the trilaminar membrane structure. Proteolysis of intact envelopes with trypsin or papain cleaves the high molecular weight polypeptides in the order E > ABP > myosin. Fragmentation occurs with cleavage of E or ABP, but does not appear to require cleavage of myosin. Actin and α-actinin are not appreciably cleaved when associated with the membrane. The results, combined with previous observations, suggest an extensive complex of cytoskeletal proteins attached to the membrane interior surface.     

Presence in human epidermal cells of a soluble protein precursor of the cross-linked envelope: activation of the cross-linking by calcium ions.

Late in the terminal differentiation of epidermis and cultured epidermal cells, a protein envelope located beneath the plasma membrane becomes cross-linked by cellular transglutaminase. The process of cross-linking can be initiated in cultured epidermal cells by agents affecting cell membrane permeability--nonionic detergents, high salt concentrations and ionophores. These agents initiate the cross-linking process by making calcium ions available to the transglutaminase. A soluble precursor of the cross-linked envelope has been identified in crude extracts of cultured epidermal cells by its ability to incorporate labeled amines through the action of transglutaminase. The protein has been purified to homogeneity by gel filtration and chromatography on columns of DEAE-cellulose and hydroxyapatite. Comprising an estimated 5--10% of the soluble cell proteins, it has a molecular weight of about 92,000, is isoelectric at pH 4.5 +/- 0.3 and has an unusual amino acid composition (46% Glx residues). It is chemically and immunochemically unrelated to keratins. The following evidence confirms that the protein becomes incorporated into cross-linked envelopes: first, washed cross-linked envelopes bind antibody to the purified protein, as shown by indirect immunofluorescence; second, absorption of the antiserum with washed envelopes removes all detectable antibodies to the purified protein; and third, the protein cannot be extracted from keratinocytes after their envelopes have become cross-linked. Examination of sections of epidermis by immunofluorescence, using antiserum to the purified protein, reveals that in addition to the stratum corneum, the living cells of the outer half of the spinous layer react strongly. The envelope precursor is present in the cytoplasm, but becomes concentrated at the cell periphery, where it will be cross-linked later, when the cells have passed through the granular layer. The protein is also concentrated in a peripheral location in cultured epidermal cells.     

Immunocytochemical evidence for a possible role of cross-linked keratinocyte envelopes in stratum corneum cohesion.

Cross-linked cornified envelopes are cell structures specifically synthesized by terminally differentiating keratinocytes. They are composed of proteins deposited at the cell periphery under the plasma membrane, and can be purified from epidermis by physicochemical extractions. The resulting keratinocyte "shells" are highly insoluble structures devoid of cytoplasmic components. The rigidity of the stratum corneum cell envelope seems to be one of the essential factors contributing to the physical resistance of this most superficial epidermal layer. We studied the purified cell envelopes from human plantar horny layer to determine their antigenic composition and protein distribution. The extraction protocol consisted of four 10-min cycles of boiling in 10 mM Tris-HCl buffer containing 2% SDS and 1% beta-mercaptoethanol. The absence of any extractable proteins persisting in the purified pellets was checked with SDS-PAGE of the sample electroeluates. Indirect immunofluorescence as well as pre- and post-embedding immunogold labeling for electron microscopy revealed the persistence of several keratinocyte antigenic determinants on the purified substrates. The antibodies directed against involucrin, keratin 10, desmoplakin I + II, desmoglein (intracellular epitope), intercellular corneodesmosome proteins, and filaggrin (a considerably weaker reactivity) labeled the cell envelopes according to the ultrastructural localization pattern characteristic for a given antigen. We conclude that the cytoskeletal and desmosomal components become "embedded" in the highly cross-linked cornified envelope structures during the process of keratinocyte terminal differentiation. This underlines the central role of cornified envelopes in the physical resistance of superficial epidermal layers and indicates a possible importance of junctional proteins in this function.     

Baculovirus-Mediated Large-Scale Expression and Purification of a Polyhistidine-Tagged Rubella Virus Capsid Protein

The capsid protein of rubella virus was produced in baculovirus-infectedSpodoptera frugiperdainsect cells, with a polyhistidine affinity tag at the carboxy terminus. The RV capsid recombinant protein was produced in a 10-liter bioreactor and purified, under nondenaturing conditions, using immobilized metal–ion affinity chromatography. Immunoblot analyses indicated that the purified recombinant protein was intact and migrated with the expected molecular weight. The final yield was 5 mg of purified protein per liter of cell culture. Surface plasmon resonance was used to investigate the antigenic potential of the histidine tagged capsid protein in an antigen–antibody interaction study. A specific interaction between the two proteins was shown. Our results suggest that this strategy should be useful in interaction studies of other virus-specific proteins and antibodies.     

Cell adhesion to tenascin-X mapping of cell adhesion sites and identification of integrin receptors.

Adhesive properties of tenascin-X (TN-X) were investigated using TN-X purified from bovine skin and recombinant proteins encompassing the RGD sequence located within the tenth fibronectin type-III domain, and the fibrinogen-like domain. Osteosarcoma (MG63) and bladder carcinoma cells (ECV304) cells were shown to adhere to purified TN-X, but did not spread and did not assemble actin stress fibers. Both cell types adhered to recombinant proteins harboring the contiguous fibronectin type-III domains 9 and 10 (FNX 9-10) but not to the FNX 10 domain alone. This adhesion to FNX 9-10 was shown to be mediated by alphavbeta3 integrin, was inhibited by RGD peptides and was strongly reduced in proteins mutated within the RGD site. As antibodies against alphavbeta3 integrin had no effects on cell adhesion to purified TN-X, we suggest that the RGD sequence is masked in intact TN-X. Cell attachment to the recombinant TN-X fibrinogen domain (FbgX) and to purified TN-X was greater for MG63 than for ECV304 cells. A beta1-containing integrin was shown to be involved in MG63 cell attachment to FbgX and to purified TN-X. Although the existence of other cell interaction sites is likely in this huge molecule, these similar patterns of adhesion and inhibition suggest that the fibrinogen domain might be a dominant site in the whole molecule.     

Mutational analysis of nocK and nocL in the nocardicin a producer Nocardia uniformis

The nocardicins are a family of monocyclic beta-lactam antibiotics produced by the actinomycete Nocardia uniformis subsp. tsuyamanensis ATCC 21806. The most potent of this series is nocardicin A, containing a syn-configured oxime moiety, an uncommon feature in natural products. The nocardicin A biosynthetic gene cluster was recently identified and found to encode proteins in keeping with nocardicin A production, including the nocardicin N-oxygenase, NocL, in addition to genes of undetermined function, such as nocK, which bears similarities to a broad family of esterases. The latter was hypothesized to be involved in the formation of the critical beta-lactam ring. While previously shown to effect oxidation of the 2'-amine of nocardicin C to provide nocardicin A, it was uncertain whether NocL was the only N-oxidizing enzyme required for nocardicin A biosynthesis. To further detail the role of NocL in nocardicin production in N. uniformis, and to examine the function of nocK, a method for the transformation of N. uniformis protoplasts to inactivate both nocK and nocL was developed and applied. A reliable protocol is reported to achieve both insertional disruption and in trans complementation in this strain. While the nocK mutant still produced nocardicin A at levels near that seen for wild-type N. uniformis, and therefore has no obvious role in nocardicin biosynthesis, the nocL disruptant failed to generate the oxime-containing metabolite. Nocardicin A production was restored in the nocL mutant upon in trans expression of the gene. Furthermore, the nocL mutant accumulated the biosynthetic intermediate nocardicin C, confirming its role as the sole oxime-forming enzyme required for production of nocardicin A.