The effect of phospholipids on the activity of isoform ACA8 of Arabidopsis thaliana plasma membrane (PM) Ca2+-ATPase was evaluated in membranes isolated from Saccharomyces cerevisiae strain K616 expressing wild type or mutated ACA8 cDNA. Acidic phospholipids stimulated the basal Ca2+-ATPase activity in the following order of efficiency: phosphatidylinositol 4-monophosphate > phosphatidylserine > phosphatidylcholine approximately = phosphatidylethanolamine approximately = 0. Acidic phospholipids increased V(max-Ca2+) and lowered the value of K(0.5-Ca2+) below the value measured in the presence of calmodulin (CaM). In the presence of CaM acidic phospholipids activated ACA8 by further decreasing its K(0.5-Ca2+) value. Phosphatidylinositol 4-monophosphate and, with lower efficiency, phosphatidylserine bound peptides reproducing ACA8 N-terminus (aa 1-116). Single point mutation of three residues (A56, R59 and Y62) within the sequence A56-T63 lowered the apparent affinity of ACA8 for phosphatidylinositol 4-monophosphate by two to three fold, indicating that this region contains a binding site for acidic phospholipids. However, the N-deleted mutant Delta74-ACA8 was also activated by acidic phospholipids, indicating that acidic phospholipids activate ACA8 through a complex mechanism, involving interaction with different sites. The striking similarity between the response to acidic phospholipids of ACA8 and animal plasma membrane Ca2+-ATPase provides new evidence that type 2B Ca2+-ATPases share common regulatory properties independently of structural differences such as the localization of the terminal regulatory region at the N- or C-terminal end of the protein.
"Phosphorylation and lipids may also affect the activity of plant plasma membrane Ca 2+ pumps. Acidic phospholipids activate a plasma membrane Ca 2+ pump from radish by a mechanism different from CaM stimulation (Bonza et al. 2001), although it appears that the phospholipid-binding site overlaps the CaM-binding site (Meneghelli et al. 2008). ACA8 is phosphorylated in vivo but the physiological impact of phosphorylation is not known (Niittyla et al. 2007). "
[Show abstract][Hide abstract] ABSTRACT: The plasma membrane separates the cellular contents from the surrounding environment. Nutrients must enter through the plasma
membrane in order to reach the cell interior, and toxic metabolites and several ions leave the cell by traveling across the
same barrier. Biological pumps in the plasma membrane include ABC transporters, vacuolar (V-type) H+ pumps, and P-type pumps. These pumps all utilize ATP as a fuel for energizing pumping. This review focuses on the physiological
roles of plasma membrane P-type pumps, as they represent the major ATP hydrolytic activity in this membrane.
"P2B-type ATPases share a number of catalytic and regulatory features      and are characterized by an extended cytosolic regulatory domain with auto-inhibitory function. The action of this domain can be suppressed by binding of calmodulin (CaM) or acidic phospholipids setting the enzyme in an activated state characterized by high V max and low K 0.5 for free Ca 2+     . Despite similar activation mechanism, some divergences can be underlined: animal isoforms of PMCAs are highly specific for ATP whereas plant ACAs have the unique ability to use GTP or ITP nearly as well as ATP   . "
[Show abstract][Hide abstract] ABSTRACT: Plant auto-inhibited Ca(2+)-ATPase 8 (ACA8) and animal plasma membrane Ca(2+)-ATPase 4b (PMCA4b) are representatives of plant and animal 2B P-type ATPases with a regulatory auto-inhibitory domain localized at the N- and C-terminus, respectively. To check whether the regulatory domain works independently of its terminal localization and if auto-inhibitory domains of different organisms are interchangeable, a mutant in which the N-terminus of ACA8 is repositioned at the C-terminus and chimeras in which PMCA4b C-terminus is fused to the N- or C-terminus of ACA8 were analysed in the yeast mutant K616 devoid of endogenous Ca(2+)-ATPases. Results show that the regulatory function of the terminal domain is independent from its position in ACA8 and that the regulatory domain belonging to PMCA4b is able to at least partially auto-inhibit ACA8.
"This possibility clearly does not apply to the trafficking of CLV1 or CLV2, based on the observation that pol pll1 mutants are fully epistatic to clv mutants, the opposite of what the trafficking model would suggest (Song et al., 2008). Furthermore, PI(4)P itself has been shown to have nontrafficking functions, including activating the Arabidopsis plasma membrane Ca 2+ -ATPase (Meneghelli et al., 2008). "
[Show abstract][Hide abstract] ABSTRACT: Stem cell maintenance and differentiation are tightly regulated in multicellular organisms. In plants, proper control of the stem cell populations is critical for extensive postembryonic organogenesis. The Arabidopsis thaliana protein phosphatase type 2C proteins POLTERGEIST (POL) and PLL1 are essential for maintenance of both the root and shoot stem cells. Specifically, POL and PLL1 are required for proper specification of key asymmetric cell divisions during stem cell initiation and maintenance. POL and PLL1 are known to be integral components of the CLE/WOX signaling pathways, but the location and mechanisms by which POL and PLL1 are regulated within these pathways are unclear. Here, we show that POL and PLL1 are dual-acylated plasma membrane proteins whose membrane localization is required for proper function. Furthermore, this localization places POL and PLL1 in proximity of the upstream plasma membrane receptors that regulate their activity. Additionally, we find that POL and PLL1 directly bind to multiple lipids and that POL is catalytically activated by phosphatidylinositol (4) phosphate [PI(4)P] in vitro. Based on these results, we propose that the upstream receptors in the CLE/WOX signaling pathways may function to either limit PI(4)P availability or antagonize PI(4)P stimulation of POL/PLL1. Significantly, the findings presented here suggest that phospholipids play an important role in promoting stem cell specification.
The Plant Cell 03/2010; 22(3):729-43. DOI:10.1105/tpc.109.068734 · 9.34 Impact Factor
Data provided are for informational purposes only. Although carefully collected, accuracy cannot be guaranteed. The impact factor represents a rough estimation of the journal's impact factor and does not reflect the actual current impact factor. Publisher conditions are provided by RoMEO. Differing provisions from the publisher's actual policy or licence agreement may be applicable.