Plant and fungal calmodulin: Ca2+-dependent regulation of plant NAD kinase

Stripe rust effector Pst03724 modulates host immunity by inhibiting NAD kinase activation by a calmodulin

Puccinia striiformis f. sp. tritici (Pst) secretes effector proteins that enter plant cells to manipulate host immune processes. In this report, we present an important Pst effector, Pst03724, whose mRNA expression level increases during Pst infection of wheat (Triticum aestivum). Silencing of Pst03724 reduced the growth and development of Pst. Pst03724 targeted the wheat calmodulin TaCaM3-2B, a positive regulator of wheat immunity. Subsequent investigations revealed that Pst03724 interferes with the TaCaM3-2B-NAD kinase (NADK) TaNADK2 association and thus inhibits the enzyme activity of TaNADK2 activated by TaCaM3-2B. Knocking down TaNADK2 expression by virus-mediated gene silencing significantly increased fungal growth and development, suggesting a decrease in resistance against Pst infection. In conclusion, our findings indicate that Pst effector Pst03724 inhibits the activity of NADK by interfering with the TaCaM3-2B-TaNADK2 association, thereby facilitating Pst infection.

Calmodulin Is the Fundamental Regulator of NADK-Mediated NAD Signaling in Plants

Calcium (Ca2+) signaling and nicotinamide adenine dinucleotide (NAD) signaling are two basic signal regulation pathways in organisms, playing crucial roles in signal transduction, energy metabolism, stress tolerance, and various developmental processes. Notably, calmodulins (CaMs) and NAD kinases (NADKs) are important hubs for connecting these two types of signaling networks, where CaMs are the unique activators of NADKs. NADK is a key enzyme for NADP (including NADP+ and NADPH) biosynthesis by phosphorylating NAD (including NAD+ and NADH) and therefore, maintains the balance between NAD pool and NADP pool through an allosteric regulation mode. In addition, the two respective derivatives from NAD+ (substrate of NADK) and NADP+ (product of NADK), cyclic ADP-ribose (cADPR) and nicotinic acid adenine dinucleotide phosphate (NAADP), have been considered to be the important messengers for intracellular Ca2+ homeostasis which could finally influence the combination between CaM and NADK, forming a feedback regulation mechanism. In this review article, we briefly summarized the major research advances related to the feedback regulation pathway, which is activated by the interaction of CaM and NADK during plant development and signaling. The theories and fact will lay a solid foundation for further studies related to CaM and NADK and their regulatory mechanisms as well as the NADK-mediated NAD signaling behavior in plant development and response to stress.

Enhanced isopropanol-butanol-ethanol mixture production through manipulation of intracellular NAD(P)H level in the recombinant Clostridium acetobutylicum XY16

BACKGROUND

The formation of by-products, mainly acetone in acetone-butanol-ethanol (ABE) fermentation, significantly affects the solvent yield and downstream separation process. In this study, we genetically engineered Clostridium acetobutylicum XY16 isolated by our lab to eliminate acetone production and altered ABE to isopropanol-butanol-ethanol (IBE). Meanwhile, process optimization under pH control strategies and supplementation of calcium carbonate were adopted to investigate the interaction between the reducing force of the metabolic networks and IBE production.

RESULTS

After successful introduction of secondary alcohol dehydrogenase into C. acetobutylicum XY16, the recombinant XY16 harboring pSADH could completely eliminate acetone production and convert it into isopropanol, indicating great potential for large-scale production of IBE mixtures. Especially, pH could significantly improve final solvent titer through regulation of NADH and NADPH levels in vivo. Under the optimal pH level of 4.8, the total IBE production was significantly increased from 3.88 to 16.09 g/L with final 9.97, 4.98 and 1.14 g/L of butanol, isopropanol, and ethanol. Meanwhile, NADH and NADPH levels were maintained at optimal levels for IBE formation compared to the control one without pH adjustment. Furthermore, calcium carbonate could play dual roles as both buffering agency and activator for NAD kinase (NADK), and supplementation of 10 g/L calcium carbonate could finally improve the IBE production to 17.77 g/L with 10.51, 6.02, and 1.24 g/L of butanol, isopropanol, and ethanol.

CONCLUSION

The complete conversion of acetone into isopropanol in the recombinant C. acetobutylicum XY16 harboring pSADH could alter ABE to IBE. pH control strategies and supplementation of calcium carbonate were effective in obtaining high IBE titer with high isopropanol production. The analysis of redox cofactor perturbation indicates that the availability of NAD(P)H is the main driving force for the improvement of IBE production.

NAD+/NADH and NADP+/NADPH in cellular functions and cell death: regulation and biological consequences

Accumulating evidence has suggested that NAD (including NAD+ and NADH) and NADP (including NADP+ and NADPH) could belong to the fundamental common mediators of various biological processes, including energy metabolism, mitochondrial functions, calcium homeostasis, antioxidation/generation of oxidative stress, gene expression, immunological functions, aging, and cell death: First, it is established that NAD mediates energy metabolism and mitochondrial functions; second, NADPH is a key component in cellular antioxidation systems; and NADH-dependent reactive oxygen species (ROS) generation from mitochondria and NADPH oxidase-dependent ROS generation are two critical mechanisms of ROS generation; third, cyclic ADP-ribose and several other molecules that are generated from NAD and NADP could mediate calcium homeostasis; fourth, NAD and NADP modulate multiple key factors in cell death, such as mitochondrial permeability transition, energy state, poly(ADP-ribose) polymerase-1, and apoptosis-inducing factor; and fifth, NAD and NADP profoundly affect aging-influencing factors such as oxidative stress and mitochondrial activities, and NAD-dependent sirtuins also mediate the aging process. Moreover, many recent studies have suggested novel paradigms of NAD and NADP metabolism. Future investigation into the metabolism and biological functions of NAD and NADP may expose fundamental properties of life, and suggest new strategies for treating diseases and slowing the aging process.

Melittin-silica, a high-pressure affinity chromatography resin for calmodulin

Calmodulin binds the peptide melittin with nanomolar affinity in the presence of Ca2+ but not in its absence. Melittin was coupled to glycidyloxypropyl-silica and used for the high-performance affinity chromatography of calmodulin. Calmodulin was retained by the resin in Ca2+-containing buffers and eluted in Ca2+-free buffers. Columns prepared from resin coupled to melittin in a batch procedure gave superior performance to those prepared under flow. Column capacity was 1.6 mg calmodulin/g resin for resins containing 1.4 mg melittin/g. Melittin-silica selectivity bound calmodulin and did not bind similar proteins such as troponin C or parvalbumin, however, other results suggest that at least one non-calmodulin protein in brain may also bind to the resin. Chromatography of crude pea plant extracts yielded homogeneous calmodulin. By modifying the standard elution protocol and/or using post-column reaction with o-phthalaldehyde, detection of less than 50 ng calmodulin in 7 min total analysis time was demonstrated. The column was used to investigate hormone- and light-induced changes in the calmodulin levels in pea plants.

Calcium-binding proteins in fungi and higher plants

Calcium has long been known to be required for many vital processes in fungi and plants. High levels of calcium are found in cell walls, vacuoles, and most organelles. In contrast, very low levels of calcium are present in the cytosol of fungal and plant cells. The most recent evidence indicates that calcium is a true second messenger in fungi and plants. Because cyclic AMP does not appear to be a second messenger in plants, calcium is the only known second messenger. Calcium-binding proteins are involved in the events that accompany the action of calcium as a second messenger; three types have been identified in fungi and plants. The first group includes several proteins that bind 45 Ca2+ and are not known to have any enzymatic activity. A second type includes the many enzymes from fungi and plants stimulated by millimolar levels of calcium. The third type of calcium-binding protein, calmodulin, responds to micromolar levels of Ca2+ by binding to certain enzymes and stimulating them. Calmodulin has been detected in every eukaryote thus far examined. The amino acid composition of several fungal and plant calmodulins have been elucidated and found to be very similar to calmodulin from animals. Eight enzymes from fungi and plants have been reported to be regulated either directly or indirectly by calmodulin. Calmodulin antagonists have been used to study the possible involvement of calmodulin in many cellular processes in fungi and plants.(ABSTRACT TRUNCATED AT 250 WORDS)

NAD+ kinase--a review

NAD+ kinase catalyzes the only (known) biochemical reaction leading to the production of NADP+ from NAD+. Most evidence indicates it is found in the cytoplasm, but reports of its presence in (other) cell bodies can not be discounted. Viewed as a protein, our knowledge of NADK composition and architecture is rudimentary. Though recognized as a large multimeric protein, no agreement is evident for the molecular weight (Mr = approximately 4-65 X 10(4] of the native protein. Is calmodulin an integral subunit of (some, all) NAD+ kinases (analogous to phosphorylase kinase in skeletal muscle)? Or is it an external modulator? Consensus is evident that a subunit of molecular weight 30-35 X 10(3) is a component of the mammalian and yeast kinase. In one case (rabbit liver) two types of subunits are reported to give rise to oligomers differing in molecular weight and catalytic activities. Viewed as an enzyme it is not known why such a complex aggregate is needed for what might otherwise appear to a routine phosphorylation reaction. Rapid equilibrium random (for pigeon liver and C. utilis preparations) and ping-pong (for A. vinelandii kinase) mechanisms have been proposed for the reaction, with multiple reactant binding sites indicated for the random cases. From the perspective of enzyme modulation, the demonstration that green plant and sea urchin egg kinases are targets for calmodulin regulation by intracellular Ca2+ links NADP+ production in these sources to the multi-level discriminatory control functions inherent to this Ca2+-protein complex. Significant questions arise from the results of various investigators considered in this review. These queries offer fertile ground for the selective design of key experiments directed to a better understanding of NAD+ kinase function and pyridine nucleotide biochemistry.

Cllmodulin in tip-growing plant cells, visualized by fluorescing calmodulin-binding phenothiazines

Calmodulin (CaM) was visualized light-microscopically by the fluorescent CaM inhibitors fluphenazine and chlorpromazine, both phenothiazines, during polar tip growth of pollen tubes of Lilium longiflorum, root hairs of Lepidium sativum, moss caulonema of Funaria hygrometrica, fungal hyphae of Achlya spec. and in the alga Acetabularia mediterranea, as well as during multipolar tip growth in Micrasterias denticulata. Young pollen tubes and root hairs showed tip fluorescence; at later stages and in the growing parts of the other subjects the fluorescence was almost uniform. After treatment with cytochalasin B, punctuate fluorescence occurred in the clear zone adjacent to the tip of pollen tubes. The observations indicate that there is CaM in all our tested systems detectable with this method. It may play a key role in starting polar growth. As in pollen tubes, CaM might be in part associated with the microfilament network at the tip, and thus regulate vesicle transport and cytoplasmic streaming.

Identification of calmodulin in the green alga Mougeotia and its possible function in chloroplast reorientational movement

A soluble protein was isolated from Mougeotia by chloropromazine-sepharose 4 B affinity chromatography. The protein matches the properties of calmodulin in terms of heat stability, Ca(2+)-dependent electrophoretic mobility in sodium-dodecyl-sulfate polyacrylamide gels, and its ability to activate cyclic nucleotide phosphodiesterase in a Ca(2+)-dependent manner. Phytochrome-mediated chloroplast reorientational movement in Mougeotia was inhibited by the calmodulin antagonist trifluoperazine, a hydrophobic compound, or N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), a hydrophilic compound; 50% inhibition (IC50) of chloroplast movement is caused by 20-50 μmol l(-1) trifluoperazine or 100 μmol l(-1) W-7. The Ca(2+)-calmodulin may act as an intermediate in the chloroplast reorientational response in Mougeotia governed by phytochrome.

Properties of a calmodulin-activated Ca2+-dependent protein kinase from wheat germ

A soluble protein kinase that is largely dependent upon Ca2+ for activity was partially purified from wheat germ. The protein kinase (Mr 90 000) catalyzes the phosphorylation of casein, histones and of endogenous proteins. Calmodulin activates the protein kinase with histone as substrate, half-maximal activation being obtained with 1.4 microM sheep brain calmodulin. The rate of casein phosphorylation is half-maximal at 0.3 microM free Ca2+ and maximal at 2.0 microM free Ca2+. Higher Ca2+ is required for histone phosphorylation, namely 80 microM and 500 microM free Ca2+, respectively, for half-maximal and maximal phosphorylation rates. In addition to Ca2+, millimolar Mg2+ is required for maximal activity of the enzyme; millimolar Mn2+ can substitute for the (Ca2+ + Mg2+) requirement. The Km for ATP is 31 microM; other nucleoside 5'-triphosphates and ADP inhibit phosphoryl transfer from ATP to protein. Serine and threonine residues of casein or histones are phosphorylated by the enzyme. The protein kinase is inhibited by relatively high concentrations of chlorpromazine and fluphenazine. The low free Ca2+ required for activation of the enzyme suggests that this type of Ca2+-dependent protein kinase may be involved in Ca2+-mediated stimulus-response coupling in plants.

Protein phosphorylation and its regulation by calcium and calmodulin in membrane fractions from zucchini hypocotyls

Protein-kinase activity has been found to be associated with a membrane fraction obtained from dark-grown zucchini (Cucurbita pepo L., cv. Senator) hypocotyl hooks. Proteins of this membrane fraction were used as protein substrates. The effects of Mg(2+), Na(+) and K(+) on phosphorylation, measured as (32)P incorporation, was investigated. The kinetics of phosphorylation of the individual protein peptides indicate the presence of specific phosphatase activity. Phosphorylation activity is strongly influenced by Ca(2+). One peptide (relative molecular weight: 180,000) exhibits strong inhibition of (32)P incorporation at physiological Ca(2+) concentrations between 0.1 and 1 μM. Phosphorylation of about 10 other proteins was enhanced by Ca(2+), being maximal in most cases at a concentration of about 3 μM free Ca(2+). Five out of these 10 peptides show increased phosphorylation in the presence of 1 μM calmodulin. This calmodulin-dependent enhancement of phosphorylation could be completely inhibited by the calmodulin antagonist fluphenazine. Cyclic AMP was found to have no stimulating effect on protein phosphorylation.

Calmodulin-dependent and independent NAD kinase activities from cytoplasmic and chloroplastic fractions of spinach (Spinacia oleracea L.)

NAD kinase activity has been found in a soluble, cytoplasmic fraction and in the chloroplasts prepared from green spinach leaves. A small amount of both the cytoplasmic and the chloroplastic NAD kinase activities was retained on a calmodulin-Sepharose affinity column. The cytoplasmic NAD kinase eluted from the affinity column was found to be enhanced by calmodulin in a Ca(2+)-dependent manner. The chloroplastic enzyme which is located exclusively in the stroma and not in the envelope and thylakoid fractions was not affected by Ca(2+) and calmodulin. The stromal fraction of purified chloroplasts contained only a negligible amount of calmodulin, most probably due to cytoplasmic contamination. Based on these data, two different mechanisms for the light-dependent modulation of spinach NAD kinase activity are suggested.