Biomedical subjects

Cunxi Wang

Publications and source records attributed to Cunxi Wang.

4 recordsLinked to original sources

PubMed2003

The oleate-stimulated phospholipase D, PLDdelta, and phosphatidic acid decrease H2O2-induced cell death in Arabidopsis.

Hydrolysis of common membrane phospholipids occurs in response to various environmental stresses, but the control and cellular function of this hydrolysis are not fully understood. Hydrogen peroxide (H2O2) is a pivotal signaling molecule involved in various stress responses. Here, we show that the plasma membrane-bound phospholipase D, PLDdelta, is activated in response to H2O2 and that the resulting phosphatidic acid (PA) functions to decrease H2O2-promoted programmed cell death. The Arabidopsis genome has 12 PLD genes, and knockout of PLDdelta abolishes specifically the oleate-stimulated PLD activity. H2O2 treatment of Arabidopsis cells activates PLD enzyme activity, and ablation of PLDdelta abolishes that activation. PLDdelta-null cells display increased sensitivity to H2O2-induced cell death. The addition of PA to PLDdelta-null cells mitigates the H2O2 effect, whereas suppression of the H2O2-induced PA formation in wild-type cells increases the effect. PLDdelta-ablated plants exhibit increased susceptibility to stress. These results demonstrate that activation of oleate-stimulated PLDdelta constitutes an important step in the plant response to H2O2 and increasing plant stress tolerance.

Apoptosis↗

PubMed2003

The calpain domain of the maize DEK1 protein contains the conserved catalytic triad and functions as a cysteine proteinase.

Development of the aleurone layer of maize grains requires the activity of the Defective kernel 1 (Dek1) gene, encoding a predicted 240-kDa membrane-anchored protein with a C terminus similar to animal calpain domain II&III. Three-dimensional modeling shows that DEK1 domain II contains a conserved calpain catalytic triad and that domain II&III has a predicted structure similar to m-calpain. Recombinant DEK1 domain II&III exhibits activity in the caseinolytic assay in the absence of calcium, although the activity is enhanced by calcium. This is in sharp contrast to animal calpains, which require Ca2+ to be active. Bacterially expressed DEK1 domain II does not display caseinolytic activity, suggesting an important role for DEK1 domain III. Mutation of the catalytic Cys residue to Ser leads to a loss of caseinolytic activity of DEK1 domain II&III. Two features of DEK1 calpain may contribute to maintaining the active site triad in an "active" configuration in the absence of Ca2+, both of which are predicted to keep m-calpain domains IIa and IIb apart. First, DEK1 lacks key charged residues in the basic loop of domain II, and secondly, the absence of an acidic loop in domain III, both of which are predicted to be neutralized upon Ca2+ binding. The Dek1 transcript is present in all cell types in developing maize endosperm, suggesting that the activity of the DEK1 calpain is regulated at the post-transcription level. The role of DEK1 in aleurone signaling is discussed.

Amino Acid Sequence↗

PubMed2002

Kinetic analysis of Arabidopsis phospholipase Ddelta. Substrate preference and mechanism of activation by Ca2+ and phosphatidylinositol 4,5-biphosphate.

Phospholipase D (PLD) is a major plant phospholipase family involved in many cellular processes such as signal transduction, membrane remodeling, and lipid degradation. Five classes of PLDs have been identified in Arabidopsis thaliana, and Ca(2+) and polyphosphoinositides have been suggested as key regulators for these enzymes. To investigate the catalysis and regulation mechanism of individual PLDs, surface-dilution kinetics studies were carried out on the newly identified PLDdelta from Arabidopsis. PLDdelta activity was dependent on both bulk concentration and surface concentration of substrate phospholipids in the Triton X-100/phospholipid mixed micelles. V(max), K(s)(A), and K(m)(B) values for PLDdelta toward phosphatidylcholine or phosphatidylethanolamine were determined; phosphatidylethanolamine was the preferred substrate. PLDdelta activity was stimulated greatly by phosphatidylinositol 4,5-bisphosphate (PIP(2)). Maximal activation was observed at a PIP(2) molar ratio around 0.01. Kinetic analysis indicates that PIP(2) activates PLD by promoting substrate binding to the enzyme, without altering the bulk binding of the enzyme to the micelle surface. Ca(2+) is required for PLDdelta activity, and it significantly decreased the interfacial Michaelis constant K(m)(B). This indicates that Ca(2+) activates PLD by promoting the binding of phospholipid substrate to the catalytic site of the enzyme.

Arabidopsis↗

PubMed2002

Networking of phospholipases in plant signal transduction.

Phospholipases are activated in response to various cellular and environmental cues. Their activation can affect many cellular processes through their roles in signal transduction. Recent advances in the biochemical and molecular understanding of phospholipase D (PLD) have provided insights into potential networks of PLDs and other phospholipases in plants. PLDs are a family of heterogeneous enzymes, and the activities of the multiple types of PLDs are regulated in distinctly different manners. Phosphoinositides, free fatty acids, lysophospholipids, and calcium are differential modulators of PLDs. Since these modulators are substrates, products, or downstream targets of phospholipase As and phospholipase Cs, there are many potential regulatory and metabolic interrelationships among the various PLDs and other phospholipases.

Journal Article↗