Phospholipases bacterial

The second type of material includes spores, which may or may not produce disease symptoms but which can germinate in the insect gut and give rise to vegetative bacterial cells which in turn may produce, and exoenzymes such as phospholipases (lecithinases) or hyaluronidase. The phospholipases may produce direct toxic symptoms owing to their action on nervous or other phospholipid-containing tissue. Hyaluronidase breaks down hyaluronic acid and produces effects on animal tissue which are morphologically similar to the breakdown of insect gut wall in the presence of microbial insecticide preparations. 

Heat-labile soluble toxin Exoenzymes (phospholipases, hyaluronidase) Vegetative bacterial cells... 

Phospholipase D is widely distributed in bacteria, fungi, plants and animals, and is present in almost all mammalian cells [3]. In mammals, it occurs as alternatively spliced products of two genes (PLD1 andPLD2) (Fig. 3). Most mammalian cells express different levels of both isoforms. Both PLD1 and PLD2 have four conserved sequences (I-IV), and sequences I and IV contain the HXKX4D (HKD) motif that is characteristic of the PLD superfamily, which includes bacterial endonucleases, phospholipid synthases, viral envelope... 

A subfamily of Rho proteins, the Rnd family of small GTPases, are always GTP-bound and seem to be regulated by expression and localization rather than by nucleotide exchange and hydrolysis. Many Rho GTPase effectors have been identified, including protein and lipid kinases, phospholipase D and numerous adaptor proteins. One of the best characterized effector of RhoA is Rho kinase, which phosphorylates and inactivates myosin phosphatase thereby RhoA causes activation of actomyosin complexes. Rho proteins are preferred targets of bacterial protein toxins ( bacterial toxins). 

A bacterial phosphatidylinositol specific phospholipase C (PI-PLC) had been available for many years before it was demonstrated to strip a number of membrane-bound proteins from eukaryotic cell surfaces [1], Such proteins are anchored by a PI moiety in which the 6 position of inositol is glycosidically linked to glucosamine, which in turn is bonded to a polymannan backbone (Fig. 3-10). The polysaccharide chain is joined to the carboxyl terminal of the anchored protein via amide linkage to ethanolamine phosphate. The presence of a free NH2 group in the glucosamine residue makes the structure labile to nitrous acid. Bacterial PI-PLC hydrolyzes the bond between DAG and phosphati-dylinositols, releasing the water-soluble protein polysac charide-inositol phosphate moiety. These proteins are tethered by glycosylphosphatidylinositol (GPI) anchors. 

Eberhard, D. A., Cooper, C. L., Low, M. G. and Holz R. W. Evidence that the inositol phospholipids are necessary for exocytosis loss of inositol phospholipids and inhibition of secretion in permeabilized cells caused by a bacterial phospholipase C and removal of ATR Biochem. J. 268 15-25, 1990. 

Many of the proteins of membranes are enzymes. For example, the entire electron transport system of mitochondria (Chapter 18) is embedded in membranes and a number of highly lipid-soluble enzymes have been isolated. Examples are phosphatidylseiine decarboxylase, which converts phosphatidylserine to phosphatidylethanolamine in biosynthesis of the latter, and isoprenoid alcohol phosphokinase, which participates in bacterial cell wall synthesis (Chapter 20). A number of ectoenzymes are present predominantly on the outsides of cell membranes.329 Enzymes such as phospholipases (Chapter 12), which are present on membrane surfaces, often are relatively inactive when removed from the lipid environment but are active in the presence of phospholipid bilay-ers.330 33 The distribution of lipid chain lengths as well as the cholesterol content of the membrane can affect enzymatic activities.332... 

An important role in the nonspecific cellular response is played by Paneth cells which line the bottom of the intestinal glands. Their granules contain compounds that can damage bacteria. These include a lysozyme which damages peptidoglycan, the basic structure of Gram positive bacterial cellular membrane secreted phospholipase A2 involved in lipopolysaccharide metabolism and a-defensins, cryptydins, which decompose bacterial proteins. 

Essentially the existence of this enzymatic activity was first established with certainty in the early 1940s in the filtrates of the bacterial organism Cl. perfringens (Cl. welchii) and has been detected subsequently in the filtrates of many other bacteria. Sloane-Stanley (1953) first presented evidence supportive of the presence of a phospholipase C in a mammalian cell, the guinea pig brain. Since that time, momentum in this field of study has increased exponentially with the exciting developments in the signal transduction field. In the latter system, stimulation of a cell leads to activation of a phospholipase C,... 

A thoughtful and detailed outline of the isolation, purification and characterization of the bacterial phospholipases C is given by Waite (1987). Procedures similar to those mentioned above for the mammalian enzymes were also useful in defining the chemistry of the bacterial phospholipases C. 

In a study designed to investigate the structural features of a phospho-glyceride interaction with a bacterial phospholipase C, El-Sayed et al. (1985), reported that the carbonyl group and its closely related environment are most important. A more detailed treatment of the substrate specificity of this enzyme can be found in an excellent review by Massing and Eibl (1994). 

In contrast to the phospholipase C of bacterial origin, there appears to be a consensus that the enzyme from mammalian sources prefers Ca2+ at millimo-lar concentrations. Interestingly, heavy metal ions such as Hg2+ or Zn2+ are strong inhibitors of this source of enzyme and EGTA must be included in the reaction mixture to chelate these cations. 

Partial coalescence is probably also involved in a defect in unhomogenized milk that has not been kept at a sufficiently low temperature, referred to as bitty cream or broken cream. Bacterial phospholipases can hydrolyse... 

As illustrated in Table I, many hormones act by stimulating membrane-bound phospholipases. The most commonly affected enzyme is a phospholipase C with specificity for phosphoinositides, i.e., a phosphoinositidase C (PIC) and, among these, the most relevant has specificity for phosphatidylinositol bisphosphate yielding inositol trisphosphate (IP3) and diacylglycerol (DAG). IP3 and DAG act as second messengers to mobilize Ca2+ from intracellular stores and activate the phospholipid- and Ca2+-dependent protein kinase, respectively (protein kinase C) (for reviews see Refs. 87-90). A typical Gp-mediated response of this type occurs in neutrophils exposed to the chemoattractant peptide fMLP [91]. fMLP binds to specific membrane receptors which recognize proteolyzed fragments of bacterial pro-... 

Lipase (Microbial) Activity for Medium- and Long-Chain Fatty Acids, (S3)105 Lysozyme Activity, (S3)106 Maltogenic Amylase Activity, 804 Milk-Clotting Activity, 805 Pancreatin Activity, 805 Pepsin Activity, 807 Phospholipase A2 Activity, 808 Phytase Activity, 808 Plant Proteolytic Activity, 810 Proteolytic Activity, Bacterial (PC), 811 Proteolytic Activity, Fungal (HUT), 812 Proteolytic Activity, Fungal (SAP), 813 Pullulanase Activity, 814 Trypsin Activity, 814 Enzyme Assays, 786 Enzyme-Hydrolyzed (Source) Protein,... 

Among the outer membrane enzymes, OmpT is a special protease that has been implicated in the pathogenicity of bacteria. It is monomeric with the active center pointing to the outside (Vandeputte-Rutten et al., 2001). Another enzyme, the phospholipase A OmpLA, produces holes in the outer membrane when it is activated. The activation process has not yet been clarified, but it is known to require a dimerization of OmpLA in the membrane. The activation by dimer formation has been verified by a crystal structure analysis of an OmpLA dimer that was produced by a reaction with an inhibitor (Snijder et al., 1999). It showed that each active center contained a catalytic triad Ser-His-Asn on one subunit and an ox-anion hole formed by an amide together with a hydrated Ca2+ ion on the other. The active centers are well placed for deacylating lipopolysaccha-rides of the external leaflet of the outer bacterial membrane. OmpLA functions in the secretion of colicins and virulence factors. 

Griffith, O.H., and Ryan, M., 1999, Bacterial phosphatidylinositol-specific phospholipase C Structure, function, and interaction with lipids. Biochim. Biophys. Acta 1441 237-254. 

Lewis, K., Garigapati, V, Zhou, C., and Roberts, M.F., 1993, Substrate requirements of bacterial phosphatidylinositol-specific phospholipase C. Biochemistry 32 8836-8841. 

All aminopeptidases identified so far contain a glycosylphosphatidyl inositol (GPI) moiety through which they anchor to membranes [123,124,143,144]. These GPI-anchored proteins may play an essential role in targeting Cry toxins to lipid raft membrane microdomains and leading to toxin aggregation and pore fimnation [145]. Removal of the GPI-anchor with bacterial or endogenous phospholipase C converts flie membrane-... 

PAPs are glycoenzymes of 35-40kDa characterized by their intense purple color due to a tyrosine ligand-to-iron(III) charge transfer transition near 600 nm. The best studied PAPs are those from bovine spleen, porcine uterine fluids, and rat bone, which have been proposed to be involved in iron transport, the immune response, and bone resorption respectively. However, the biological relevance of the phosphatase activity of PAPs has not been unequivocally established. Recently, a bacterial phospholipase with active site properties resembling those of PAPs has also been reported. All PAPs contain a conserved dimetal binding... 

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