Purification of G-protein-regulated phospholipase C from turkey erythrocytes

Phospholipidic signaling and vanillin production in response to salicylic acid and methyl jasmonate in Capsicum chinense J. cells

The phospholipidic signal transduction system involves generation of second messengers by hydrolysis or changes in phosphorylation state. Several studies have shown that the signaling pathway forms part of plant response to phytoregulators such as salicylic acid (SA) and methyl jasmonate (MJ), which have been widely used to stimulate secondary metabolite production in cell cultures. An evaluation was made of the effect of SA and MJ on phospholipidic signaling and capsaicinoid production in Capsicum chinense Jacq. suspension cells. Treatment with SA inhibited phospholipase C (PLC) (EC: 3.1.4.3) and phospholipase D (PLD) (EC: 3.1.4.4) activities in vitro, but increased lipid kinase activities in vitro at different SA concentrations. Treatment with MJ produced increases in PLC and PLD activities, while lipid kinase activities were variable and dose-dependent. The production of vanillin, a precursor of capsaicinoids, increased at specific SA or MJ doses. Preincubation with neomycin, a phospholipase inhibitor, before SA or MJ treatment inhibits increase in vanillin production which suggests that phospholipidic second messengers may participate in the observed increase in vanillin production.

GTPgammaS antagonizes the mastoparan-induced in vitro activity of PIP-phospholipase C from symbiotic root nodules of Phaseolus vulgaris

Phospholipase C (PLC) has been suggested to have a role in signal perception by Nod factors (NFs) in legume root hair cells. For instance, mastoparan, a well-described agonist of heterotrimeric G protein, induces nodulin expression after NFs treatment or Rhizobium inoculation. Furthermore, it has been recently demonstrated that mastoparan also mimics calcium oscillations induced by NFs, suggesting that PLC could play a key role during the nodulation process. In this study, we elucidate a biochemical relationship between PLC and heterotrimeric G proteins during NFs signaling in legumes. In particular, the effect of NFs on in vitro PLC activity from nodule membrane fractions in the presence of guanosine 5'-[gamma-thio]triphosphate (GTPgammaS) and mastoparan was assayed. Our results indicate that for phosphatidylinositol 4,5 bisphosphate (PIP(2))-PLC, there is a specific activity of 20-27 nmol mg(-1) min(-1) in membrane fractions of nodules 18-20 days after inoculation with Rhizobium tropici. Interestingly, in the presence of 5 microM mastoparan, PIP(2)-PLC activity was almost double the basal level. In contrast, PIP(2)-PLC activity was downregulated by 1-10 microM GTPgammaS. Also, PLC activity was decreased by up to 64% in the presence of increasing concentrations of NFs (10(-8) to 10(-5) M). NFs are critical signaling molecules in rhizobia/legume symbiosis that can activate many of the plant's early responses during nodule development. Calcium spiking, kinases, PLC activity and possibly G proteins appear to be components downstream of the NFs perception pathway. Our results suggest the occurrence of a dual signaling pathway that could involve both G proteins and PLC in Phaseolus vulgaris during the development of root nodules.

Membrane-associated phosphoinositides-specific phospholipase C forms from Catharanthus roseus transformed roots

We have previously reported that Catharanthus roseus transformed roots contain at least two phosphatidylinositol 4,5-bisphosphate-phospholipase C (PLC) activities, one soluble and the other membrane associated. Detergent, divalent cations, and neomycin differentially regulate these activities and pure protein is required for a greater understanding of the function and regulation of this enzyme. In this article we report a partia purification of membrane-associated PLC. We found that there are at least two forms of membraneassociated PLC in transformed roots of C. roseus. These forms were separated on the basis of their affinity for heparin. One form shows an affinity for heparin and elutes at approx 600 mM KCl. This form has a molecular mass of 67 kDa by size exclusion chromatography and Western blot analysis, whereas the other form does not bind to heparin and has a molecular mass of 57 kDa. Possible differential regulation of these forms during transformed root growth is discussed.

Aluminium-induced phospholipid signal transduction pathway in Coffea arabica suspension cells and its amelioration by silicic acid

Coffee (Coffea arabica L.) is of economic importance worldwide. Its growth in organic-rich acidic soils is influenced by aluminium such that coffee yield may be impaired. Herein we have used the Al-sensitive C. arabica suspension cell line L2 to analyse the effect of two different Al species on the phosphoinositide signal transduction pathway. Our results have shown that the association of Al with coffee cells was affected by the pH and the form of Al in media. More Al was associated with cells at pH 4.3 than 5.8, whereas when Al was present as hydroxyaluminosilicates (HAS) the association was halved at pH 4.3 and unchanged at pH 5.8. Two signal transduction elements were also evaluated; phospholipase C (PLC) activity and phosphatidic acid (PA) formation. PLC was inhibited ( approximately 50%) when cells were incubated for 2 h in the presence of either AlCl(3) or Al in the form of HAS. PA formation was tested as a short-term response to Al. By way of contrast to what was found for PLC, incubation of cells for 15 min in the presence of AlCl(3) decreased the formation of PA whereas the same concentration of Al as HAS produced no effect upon its formation. These results suggest that Al is capable to exert its effects upon signal transduction as Al((aq))(3+) acting upon a mechanism linked to the phosphoinositide signal transduction pathway.

Polyamines modify the components of phospholipids-based signal transduction pathway in Coffea arabica L. cells

Recent results, fundamentally obtained from animal tissues, suggest that polyamines (Pas), essential compounds for the growth and development of all life organisms, may interact with a signal transduction cascade. Because Pas are highly positive charged compounds, their binding with phospholipids involved in signal transduction is likely to be the case. In this work, the in vivo effect of Pas on some important components of phospholipid signal transduction pathway was studied, by the first time, in plant tissue. Endogenous Pas content varied during the culture cycle of Coffea arabica cells: putrescine (Put) levels increased at the end of the stationary phase, both spermidine (Spd) and spermine (Spm) accumulated at the beginning of the linear growth phase. Cells that were incubated with Put presented a significant increase in phospholipase D (PLD) (EC: 3.1.4.4) activity, phospholipase C (PLC) (EC: 3.1.4.3) activity decreased, and the effect on lipid kinases was less marked. However, the incubation of the cells with Spd and Spm significantly stimulated the lipid kinases activities, fundamentally increased the formation of phosphatidyl inositol 4-phosphate (PIP) and phosphatidylinositol 4,5-bisphosphate (PIP2), while the effect on PLC and PLD activities was minor when compared with the cells treated with Put. The results presented here suggest that Pas may modulate the cellular signal of C. arabica cells by differentially affecting components of the phospholipid cascade.

Phospholipase C activity from Catharanthus roseus transformed roots: aluminum effect

The effect of aluminum on the activity of PLC was examined in transformed roots from Catharanthus roseus (L) G. Don. When added in vitro to the reaction mixture, Al inhibited the enzymatic activity in a concentration and time-dependent fashion. This effect is very similar for both activities (soluble and membrane-associated). When roots were treated in vivo with Al 0.1 mM for short periods (0-4 h), PLC activity was also inhibited. Aluminum (1 mM) diminished root growth in approximately 50% when added on the first day of the culture cycle conditions in which PLC activity is also affected. Other enzymatic activities (NAD+-GDH, NADH-GDH, NADH-GOGAT and HMGR) were not affected when roots were treated with Al (0.1 mM) for short periods of time (1 h). Results obtained in this work suggest that the Al can affect PLC activity as a specific target. Enzymes: Phospholipase C (EC 3.1.4.10).

Kinetic analysis of phospholipase C from catharanthus roseus transformed roots using different assays

The properties of phospholipase C (PLC) partially purified from Catharanthus roseus transformed roots were analyzed using substrate lipids dispersed in phospholipid vesicles, phospholipid-detergent mixed micelles, and phospholipid monolayers spread at an air-water interface. Using [(33)P]phosphatidylinositol 4,5-bisphosphate (PIP(2)) of high specific radioactivity, PLC activity was monitored directly by measuring the loss of radioactivity from monolayers as a result of the release of inositol phosphate and its subsequent dissolution on quenching in the subphase. PLC activity was markedly affected by the surface pressure of the monolayer, with reduced activity at extremes of initial pressure. The optimum surface pressure for PIP(2) hydrolysis was 20 mN/m. Depletion of PLC from solution by incubation with sucrose-loaded PIP(2) vesicles followed by ultracentrifugation demonstrated stable attachment of PLC to the vesicles. A mixed micellar system was established to assay PLC activity using deoxycholate. Kinetic analyses were performed to determine whether PLC activity was dependent on both bulk PIP(2) and PIP(2) surface concentrations in the micelles. The interfacial Michaelis constant was calculated to be 0.0518 mol fraction, and the equilibrium dissociation constant of PLC for the lipid was 45.5 &mgr;M. These findings will add to our understanding of the mechanisms of regulation of plant PLC.

Effect of different inhibitors on phospholipase C activity in Catharanthus roseus transformed roots

We have previously reported that Catharanthus roseus transformed roots contain at least two phosphatidylinositol 4,5-bisphosphate-phospholipase C (PLC) activities, one soluble and one membrane associated. In this paper, the effect of neomycin and several divalent cations was analyzed, both in the soluble and the membrane-associated PLC activity in C. roseus transformed roots. In this system, neomycin, an aminoglycoside antibiotic, inhibited PLC in a concentration-dependent fashion. The neomycin IC50 (100 microM) was the same for the inhibition of the soluble and the membrane associated PLC activity. The effect of different divalent cations such as Ni2+, Cu2+, and Zn2+ was studied as well. In order to see the effect of these cations on PLC activity, we selected two conditions: a) in the presence of and b) in the absence of calcium. In the presence of calcium, these three divalent cations were able to inhibit PLC activity in both fractions in a concentration-dependent manner; however, the IC50s were different for the membrane and the soluble activities. For the soluble activity, the inhibition due to the three cations was very similar (IC50s between 0.2 and 0.3 mM). For the membrane associated PLC activity, Cu2+ was the most potent inhibitor (IC50 3.6 microM), then Ni2+ and then Zn2+. In the absence of calcium, higher concentrations of Cu2+ and Zn2+ demonstrated some inhibitory effect. We discuss the possible physiological role of these inhibitors on PLC activity.

Molecular cloning, expression and regulatory activity of G alpha 11- and beta gamma-subunit-stimulated phospholipase C-beta from avian erythrocytes

A turkey erythrocyte phospholipase C (PLC) has been instrumental in delineating the role of G-proteins in receptor-regulated inositol lipid signalling. This isoenzyme is uniquely regulated both by alpha-subunits of the Gq family and by G-protein beta gamma-subunits. A 4819 bp cDNA encoding this PLC has been cloned from a turkey erythrocyte cDNA library. The open reading frame of this cDNA encodes a 1211-amino-acid protein (calculated molecular mass 139050 Da) that contains amino acid sequences of 16 peptides sequenced from the turkey erythrocyte PLC. The predicted sequence of the turkey PLC shows considerable similarity with the sequences of previously cloned members of the PLC-beta family, with the highest identity (71%) shared with PLC-beta 2 and lesser identities observed with PLC-beta 1 (49%), PLC-beta 3 (46%) and PLC-beta 4 (37%). The largest differences in sequence between the turkey PLC-beta and other PLC-beta isoenzymes occur in the C-terminal domain and in the region between the X- and Y-domains. The turkey isoenzyme and PLC-beta 2, which differ in their regulation by G-protein alpha-subunits, are only 44% similar across the approx. 400 amino acid residues of the C-terminal domain that has been implicated in alpha q activation of these proteins. Recombinant turkey PLC-beta was purified to homogeneity following expression from a recombinant baculovirus in Sf9 insect cells. The immunoreactivity and mobility on SDS/PAGE of the recombinant enzyme were the same as observed with native turkey erythrocyte PLC-beta. Moreover, the catalytic activities of the recombinant enzyme were indistinguishable from those of native turkey erythrocyte PLC-beta in assays carried out in the presence of cholate and Ca2+, or in assays of activity after reconstitution with G alpha 11 or G-protein beta gamma-subunits. The turkey PLC-beta was more sensitive to activation by G alpha 11 than was PLC-beta 2, and was more sensitive to activation by beta gamma-subunits than either PLC-beta 2 or PLC-beta 1.

Kinetic analysis of phospholipase C beta isoforms using phospholipid-detergent mixed micelles. Evidence for interfacial catalysis involving distinct micelle binding and catalytic steps

Phosphatidylinositol 4,5-bisphosphate (PtdIns (4,5)-P2) hydrolysis by three different beta-isoforms of phospholipase C (PLC) was examined to investigate the catalytic action of these extracellular signal-regulated enzymes. Depletion of phospholipase C from solution by incubation with sucrose-loaded vesicles of differing compositions followed by ultracentrifugation demonstrated stable attachment of PLC to the vesicles from which an equilibrium association constant of PLC with PtdIns (4,5)P2 could be determined. A mixed micellar system was established to assay PLC activity using dodecyl maltoside, which behaved as an essentially inert diluent of PtdIns (4,5)P2 with respect to PLC beta activity. Kinetic analyses were performed to test whether PLC beta activity was dependent on both bulk PtdIns (4,5)P2 concentration and surface concentration in the micelles as has been shown for other lipid metabolising enzymes. Each of the PLC beta isoforms behaved similarly in these analyses, which indicated the involvement of at least two binding events. Interfacial Michaelis constants were calculated to be between 0.1-0.2 mol fraction for all three enzymes, and Ks (the equilibrium dissociation constant of PLC for lipid) ranged between 100-200 microM. The apparent multiple interfacial binding events did not appear to result from lipid-induced PLC beta oligomerization implying that PLC beta monomers possess more than one lipid-binding site. Surface dilution of PLC-catalyzed PtdIns (4,5)P2 hydrolysis was assessed in the presence of increasing concentrations of various nonsubstrate phospholipids, which profoundly reduced PLC activity, suggesting that these lipids may inhibit enzyme action. The data indicate that G protein-regulated isoforms of PLC operate with separate lipid binding and catalytic steps and imply that under physiological conditions, PLC beta isoforms operate under first-order conditions. These findings may have implications for the mechanisms of regulation of PLC beta s by G protein subunits.