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Query: UMLS:C0026936 (Mycoplasma)
 14,761 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Thermoplasma acidophilum, a mycoplasma-like organism, grows optimally at 56 degrees C and pH2. The low temperature extreme of growth is 37 degrees C. The plasma membrane of cells grown at 37 degrees C was isolated and characterized physicobiochemically. Membrane lipids which comprise 25% of the membrane dry weight consist mainly of two repetitively methyl-branched C40 side chains that were ether-linked to two glycerol molecules. The lipid structures were elucidated by combined gas chromatography-mass spectroscopy, direct probe mass spectroscopy and 13C NMR. 37 degrees C-grown cells contained lipids with 42% more pentane cyclization than the 56 degrees C-grown cells. In 37 degrees C-grown cells, phospholipid and serine content decreased by about 10% each, carbohydrate content increased by 5%. EPR studies demonstrated an increase in membrane lipid fluidity of 37 degrees C-grown cells with an upper transition temperature at 35 degrees C which was shifted down by 10 degrees C compared with cells grown at 56 degrees C. Membrane-bound ATPase activities also indicated similar changes upon adaptation. There is a close correlation between membrane fluidity and physiological functioning of this membrane-bound enzyme.
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PMID:Structure of membrane lipids and physico-biochemical properties of the plasma membrane from Thermoplasma acidophilum, adapted to growth at 37 degrees C. 22 Oct 32

The genetic code, formerly thought to be frozen, is now known to be in a state of evolution. This was first shown in 1979 by Barrell et al. (G. Barrell, A. T. Bankier, and J. Drouin, Nature [London] 282:189-194, 1979), who found that the universal codons AUA (isoleucine) and UGA (stop) coded for methionine and tryptophan, respectively, in human mitochondria. Subsequent studies have shown that UGA codes for tryptophan in Mycoplasma spp. and in all nonplant mitochondria that have been examined. Universal stop codons UAA and UAG code for glutamine in ciliated protozoa (except Euplotes octacarinatus) and in a green alga, Acetabularia. E. octacarinatus uses UAA for stop and UGA for cysteine. Candida species, which are yeasts, use CUG (leucine) for serine. Other departures from the universal code, all in nonplant mitochondria, are CUN (leucine) for threonine (in yeasts), AAA (lysine) for asparagine (in platyhelminths and echinoderms), UAA (stop) for tyrosine (in planaria), and AGR (arginine) for serine (in several animal orders) and for stop (in vertebrates). We propose that the changes are typically preceded by loss of a codon from all coding sequences in an organism or organelle, often as a result of directional mutation pressure, accompanied by loss of the tRNA that translates the codon. The codon reappears later by conversion of another codon and emergence of a tRNA that translates the reappeared codon with a different assignment. Changes in release factors also contribute to these revised assignments. We also discuss the use of UGA (stop) as a selenocysteine codon and the early history of the code.
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PMID:Recent evidence for evolution of the genetic code. 157 11

Deviations from the universal genetic code have been reported for several microorganisms. Termination codons are used for coding some amino acids in Paramecium, Mycoplasma or Tetrahymena, and in Escherichia coli, the UGA termination codon is used to code for selenocysteine. In mitochondria, the changes of sense codons to termination codons or to codons encoding other amino acids have also been reported. Here we report another example of divergence from the universal code, this time in a non-spore-forming yeast Candida cylindracea, in which the universal codon for leucine, CUG, is used to code for serine. This conclusion is based on the observations that: (1) the amino-acid composition and the partial amino-acid sequences of an extracellular lipase from this yeast agreed with those deduced from the complementary DNA if CUG was assumed to specify serine; and (2) serine, but not leucine, was incorporated into a polypeptide in a cell-free translation system from this yeast in the presence of a synthetic CUG oligomer.
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PMID:The codon CUG is read as serine in an asporogenic yeast Candida cylindracea. 250 50

We report a cluster of four tRNA genes from Mycoplasma mycoides as well as the sequence of the alanine, proline, and valine tRNAs and the serine tRNA reading the UCN codons (where N stands for G, A, C, or U). This brings the total number of tRNA genes that we have so far characterized in this organism to 14, 6 of which code for tRNAs that read the codons of family boxes. In each of these latter cases, we found only one gene per family box, and the gene sequence contains a thymidine in the position corresponding to the wobble nucleotide, with the exception of the arginine tRNA gene that has an adenosine in this position. Furthermore, all of the tRNA structures reported here have an unsubstituted uridine in the wobble position. These findings are similar to those reported for mitochondria, especially yeast mitochondria, that contain an arginine tRNA with the anticodon ACG. However, the resemblance is not complete since we have demonstrated the presence of two isoacceptor tRNAs for threonine having uridine and adenosine, respectively, in the wobble position. It is suggested that in the M. mycoides at least some of the family codon boxes are read by only one tRNA each, using an unconventional method without discrimination between the nucleotides in the third codon position.
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PMID:Apparent lack of discrimination in the reading of certain codons in Mycoplasma mycoides. 355 32

Aminopeptidase activity was demonstrated in Mycoplasma salivarium (ATCC 23064) cells disrupted by sonic vibrations and lyophilized (crude enzymes), and weak endopeptidase or carboxypeptidase activity was also suggested. The crude enzymes were suspended in 0.1 M borate buffer, pH 8.0, containing 0.5% (w/v) sodium deoxycholate, and then the suspensions were centrifuged at 100,000 g for 2 h. Thus separated, the supernatants were applied to a column of Sephacryl S-300. As a result, aminopeptidase activity was separated from caseinolytic activity, which had already been demonstrated in this organism. The aminopeptidase activity was inhibited by o-phenanthroline and stimulated by Mn2+, and the enzyme exhibited a strong affinity for leucine and arginine. On the other hand, the caseinolytic activity was inhibited considerably by o-phenanthroline and Ni2+ and slightly by diisopropyl fluorophosphate and Co2+. The caseinolytic activity was therefore believed to be due mainly to metalloproteinases and partly to serine proteinases.
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PMID:Aminopeptidase and caseinolytic activities of Mycoplasma salivarium. 637 68

GTP, as well as other nucleoside triphosphates, stimulates the activity of Escherichia coli adenylyl cyclase in permeable cells; the stimulatory effect is lost when the cells are disrupted by passage through a French pressure cell. These data suggested that the allosteric regulation by GTP of adenylyl cyclase activity requires an interaction of the enzyme with other protein factors. Strains deleted for genes encoding proteins of the phosphoenolpyruvate:sugar phosphotransferase system (PTS) failed to show an activity stimulation by GTP. With a view to localizing the site of interaction of GTP with the adenylyl cyclase complex, a variety of studies using purified PTS proteins were performed using the photoaffinity labeling reagent, 8-azidoGTP. These studies showed that 8-azidoGTP bound specifically to HPr. A species specificity study showed that the photoaffinity reagent labeled E. coli HPr but not HPr proteins from Mycoplasma capricolum or Bacillus subtilis. A variety of site-directed mutations of E. coli HPr were evaluated for interaction with GTP by photoaffinity labeling as well as by nuclear magnetic resonance; the results of these studies indicate that the lysine residues at positions 24 and 27, serine-46, the threonine at position 36, and the aspartate at position 69 are important for the binding of GTP to HPr. Molecular modeling has been used to formulate a model for the binding of GTP to HPr involving electrostatic interaction of the phosphate groups of the nucleotide with the side chains of lysine residues 27 and 45 and serine-43, interaction of the sugar with serine-46, and interaction of the base with lysine-24. From these data, it is hypothesized that the binding of GTP to HPr is required for the GTP-dependent stimulation of the activity of the adenylyl cyclase complex.
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PMID:The Escherichia coli adenylyl cyclase complex: requirement of PTS proteins for stimulation by nucleotides. 761 94

A cell-free system was used to characterize the phosphorylation of Mycoplasma pneumoniae proteins HMW1 and HMW2, which are involved in the adherence of this organism to human tracheal epithelium during infection. The pH and cation requirements for phosphorylation of HMW1 and HMW2 were determined, and the effects of glycolytic intermediates, cyclic AMP, and eukaryotic kinase-phosphatase inhibitors and stimulators on this process were examined. Phosphoamino acid analysis identified serine as the major phosphate acceptor for both HMW1 and HMW2 in this system.
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PMID:Phosphorylation of Mycoplasma pneumoniae cytadherence-accessory proteins in cell extracts. 763 46

Total lipid extracts were obtained from SH-SY5Y human neuroblastoma cells grown to confluency in mycoplasma-free 10% fetal calf serum. The major glycerophospholipid classes and free diacylglycerols (DAG) were isolated and quantitated by silicic acid and DEAE-cellulose column and thin-layer chromatography. The choline (CGPL), ethanolamine (EGPL), serine (SGPL), and inositol (IGPL) glycerophospholipids were converted to the corresponding diradylglycerols by phospholipase C. The molecular species of the diradylglycerols were determined by capillary gas-liquid chromatography of the trimethylsilyl or t-butyldimethylsilyl ethers. The CGPL was rich in the oligoenoic species and IGPL was rich in the polyenoic species, especially the 18:0-20:4(n-6). The EGPL contained 30-40% diacyl, 60-64% alkenylacyl, and 1-3% alkylacyl species, which were also rich in polyenoic derivatives. Small amounts of alkenylacyl species were detected also in CGPL. The cellular DAG possessed a molecular species composition halfway between those of the DAG moieties of CGPL and IGPL. The cells grown in the presence of 10% calf serum exhibited great variability in the content of 20:3(n-9) fatty acid, which was found to substitute for the 20:4(n-6) acid in the molecular species with 18:0 in both IGPL and DAG. The 20:3(n-9) was largely absent from the CGPL, but occurred also in EGPL, where it was preferentially associated with 18:0 in the diacyl but with 18:1 in the alkylacyl and alkenylacyl species. The detailed documentation of molecular species of glycerophospholipids of the neuroblastoma cells offers new opportunities for identification of the source of free DAG released in transmembrane signalling.
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PMID:Molecular species of glycerophospholipids and diacylglycerols of cultured SH-SY5Y human neuroblastoma cells. 839 72

The phosphocarrier protein, HPr, from Gram-positive organisms and mycoplasmas is a substrate for an ATP-dependent kinase that phosphorylates serine 46. In Gram-negative organisms, the corresponding HPr is not phosphorylated on serine 46 and the ATP-dependent kinase is absent. To determine the specificity requirements for phosphorylation of Mycoplasma capricolum HPr, a chimera in which residues 43-57 were replaced by the Escherichia coli sequence was constructed. The chimeric protein folded properly, but was not phosphorylated on either serine 46 or histidine 15. A dissection of the region required for phosphorylation specificity was carried out by further mutagenesis. The deficiency in phosphorylation at histidine 15 was localized primarily to the region including residues 51-57. Activity studies revealed that residues 48, 49, and 51-53 are important for recognition of M. capricolum HPr by its cognate HPr(Ser) kinase. The characteristics of this region suggest that the kinase-HPr interaction occurs mainly through a hydrophobic region. Molecular modeling comparisons of M. capricolum HPr and the chimeric construct provided a basis for interpreting the results of the activity assays.
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PMID:Topography of the interaction of HPr(Ser) kinase with HPr. 971 98

Inspection of the genomes for the bacteria Bacillus subtilis 168, Borrelia burgdorferi B31, Escherichia coli K-12, Haemophilus influenzae KW20, Helicobacter pylori 26695, Mycoplasma genitalium G-37, and Synechocystis sp PCC 6803 and for the archaeons Archaeoglobus fulgidus VC-16 DSM4304, Methanobacterium thermoautotrophicum delta H, and Methanococcus jannaschii DSM2661 revealed that each contains at least one ORF whose predicted product displays sequence features characteristic of eukaryote-like protein-serine/threonine/tyrosine kinases and protein-serine/threonine/tyrosine phosphatases. Orthologs for all four major protein phosphatase families (PPP, PPM, conventional PTP, and low molecular weight PTP) were present in the bacteria surveyed, but not all strains contained all types. The three archaeons surveyed lacked recognizable homologs of the PPM family of eukaryotic protein-serine/threonine phosphatases; and only two prokaryotes were found to contain ORFs for potential phosphatases from all four major families. Intriguingly, our searches revealed a potential ancestral link between the catalytic subunits of microbial arsenate reductases and the protein-tyrosine phosphatases; they share similar ligands (arsenate versus phosphate) and features of their catalytic mechanism (formation of arseno-versus phospho-cysteinyl intermediates). It appears that all prokaryotic organisms, at one time, contained the genetic information necessary to construct protein phosphorylation-dephosphorylation networks that target serine, threonine, and/or tyrosine residues on proteins. However, the potential for functional redundancy among the four protein phosphatase families has led many prokaryotic organisms to discard one, two, or three of the four.
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PMID:The serine, threonine, and/or tyrosine-specific protein kinases and protein phosphatases of prokaryotic organisms: a family portrait. 986 22


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