Phospholipid requirement of the vanadate-sensitive ATPase from maize roots evaluated by two methods

Anionic Phospholipids Stimulate the Proton Pumping Activity of the Plant Plasma Membrane P-Type H+-ATPase

The activity of membrane proteins depends strongly on the surrounding lipid environment. Here, we characterize the lipid stimulation of the plant plasma membrane H+-ATPase Arabidopsis thaliana H+-ATPase isoform 2 (AHA2) upon purification and reconstitution into liposomes of defined lipid compositions. We show that the proton pumping activity of AHA2 is stimulated by anionic phospholipids, especially by phosphatidylserine. This activation was independent of the cytoplasmic C-terminal regulatory domain of the pump. Molecular dynamics simulations revealed several preferential contact sites for anionic phospholipids in the transmembrane domain of AHA2. These contact sites are partially conserved in functionally different P-type ATPases from different organisms, suggesting a general regulation mechanism by the membrane lipid environment. Our findings highlight the fact that anionic lipids play an important role in the control of H+-ATPase activity.

Plant lipid environment and membrane enzymes: the case of the plasma membrane H+-ATPase

Several lipid classes constitute the universal matrix of the biological membranes. With their amphipathic nature, lipids not only build the continuous barrier that confers identity to every cell and organelle, but they are also active actors that modulate the activity of the proteins immersed in the lipid bilayer. The plasma membrane H(+)-ATPase, an enzyme from plant cells, is an excellent example of a transmembrane protein whose activity is influenced by the hydrophilic compartments at both sides of the membrane and by the hydrophobic domains of the lipid bilayer. As a result, an extensive documentation of the effect of numerous amphiphiles in the enzyme activity can be found. Detergents, membrane glycerolipids, and sterols can produce activation or inhibition of the enzyme activity. In some cases, these effects are associated with the lipids of the membrane bulk, but in others, a direct interaction of the lipid with the protein is involved. This review gives an account of reports related to the action of the membrane lipids on the H(+)-ATPase activity.

Effect of phytotoxic resin glycoside on activity of H(+)-ATPase from plasma membrane

A resin glycoside mixture isolated fromIpomoea tricolor inhibited radicle growth ofEchinochloa crusgalli. The effect of the resin was tested on the activity of the plasma membrane H(+)-ATPase fromE. crusgalli. For this purpose, plasma membrane vesicles were purified by the method of aqueous two-phase partitioning. The resin glycoside inhibited by 30% the activity of the plasma membrane ATPase. The same result was obtained with the purified main component of the resin. This indicates that the plasma membrane ATPase can be one of the cellular targets of the resin. Hence it is possible that the mechanism of action of the resin involves an inhibition of the plasma membrane ATPase.

Regulation of plasma membrane H+-ATPase activity by the membrane environment

The plant plasma membrane H(+)-ATPase is a proton pump which plays a central role in physiological functions such as nutrient uptake and intracellular pH regulation. This pump belongs to the P(3)-type ATPase family and creates an electrochemical gradient across the plasma membrane. The generation of this gradient has a major role in providing the energy for secondary active transport across the plasma membrane. The activity of the proton pump is regulated by the transcriptional and post-translational levels and by membrane environmental factors such as membrane lipids. Several reviews have appeared during the last few years concerning the regulatory mechanism at transcriptional and post-translational levels. The plasma membrane H(+)-ATPase requires lipids for activity. This lipid dependency suggests a possible mode of regulation of the H(+)-ATPase via modification of its lipid environment. This review focuses on the regulation of plasma membrane H(+)-ATPase by membrane lipids surrounding H(+)-ATPase molecules.

Sterol Modulation of the Plasma Membrane H+-ATPase Activity from Corn Roots Reconstituted into Soybean Lipids

A partially purified H+-ATPase from the plasma membrane (PM) of corn (Zea mays L.) roots was inserted into vesicles prepared with soybean (Glycine max L.) phospholipids and various concentrations of individual sterols using either a freeze-thaw sonication or an octylglucoside dilution procedure. Both methods yielded a functional enzyme that retained its native characteristics. We have investigated the effects of typical plant sterols (i.e. sitosterol, stigmasterol, and 24-methylcholesterol) on both ATP hydrolysis and H+ pumping by the reconstituted corn root PM ATPase. We have also checked the influence of cholesterol and of two unusual sterols, 24-methylpollinastanol and 14[alpha],24-dimethylcholest-8-en-3[beta]-ol. Here we present evidence for a sterol modulation of the plant PM H+-ATPase activity. In particular, cholesterol and stigmasterol were found to stimulate the pump, especially when present at 5 mol%, whereas all of the other sterols tested behaved as inhibitors at any concentration in proteoliposomes. In all situations H+ pumping was shown to be more sensitive to a sterol environment than was ATP hydrolysis. Our results suggest the occurrence of binding sites for sterols on the plant PM H+-ATPase.

Lysophosphatidylcholine specifically stimulates plasma membrane H(+)-ATPase from corn roots

The plasma membrane H(+)-ATPase activity from corn seedling roots is shown to be stimulated 3- to 4-fold by the addition of lysophosphatidylcholine (lysoPC). This effect clearly differs from that of other detergents by both the magnitude and the absence of inhibition at higher concentrations. LysoPC decreases the apparent Km for MgATP, increases Vmax of the ATPase reaction but does not change its pH optimum. On the contrary, the acid phosphatase activity associated with plasma membranes is not influenced by lysoPC. A lysoPC stimulation is also demonstrated for the solubilized preparation of the H(+)-ATPase. It is assumed that lysoPC stimulation of the plant plasma membrane H(+)-ATPase is not only due to permeabilization of the vesicles for MgATP, but also to direct action on the enzyme.

Mechanism for the Activation of Plasma Membrane H-ATPase from Rice (Oryza sativa L.) Culture Cells by Molecular Species of a Phospholipid

The activation of H(+)-ATPase solubilized from plasma membrane of rice (Oryza sativa L. var Nipponbare) culture cells was examined by the exogenous addition of various phospholipids, free fatty acids, glycerides, polar head groups of phospholipids and molecular species of phosphatidylcholine (PC). H(+)-ATPase activity appeared to be stimulated by phospholipids in the following order: asolectin > phosphatidylserine > PC > lysophosphatidylcholine > phosphatidylglycerol, and maximal ATPase activation was noted at around 0.05 to 0.03% (w/v) of asolectin or molecular species of PC. Polar head groups such as glycerol, inositol, and serine only slightly activated ATPase activity or not at all, while ethanolamine and choline had no effect. Activation was dependent on the degree of saturation or unsaturation of the fatty acyl chain and its length. The activity decreased with increase in the length of fatty acyl chain from dimyristoryl(14:0)-PC to distearoyl(18:0)-PC and the degree of unsaturation from dioleoyl(18:1)-PC to dilinolenoyl(18:3)-PC. Maximum activation was observed when PC possessing 1-myristoyl(14:0)-2-oleoyl(18:1) or 1-oleoyl-2-myristoyl was added to the reaction mixture. These data show that the activation of plasma membrane H(+)-ATPase by PC depends on a combination of saturated (myristic acid 14:0, palmitic acid 16:0, and stearic acid 18:0) and unsaturated (oleic acid 18:1, linoleic acid 18:2, and arachidonic acid 20:4) fatty acids at the sn-1 and sn-2 positions of the triglycerides.