Isolation of the catalytic subunit of a membrane-bound H(+)-pyrophosphatase from pea stem mitochondria

Glucose/Ribitol Dehydrogenase and 16.9 kDa Class I Heat Shock Protein 1 as Novel Wheat Allergens in Baker’s Respiratory Allergy

Wheat allergens are responsible for symptoms in 60–70% of bakers with work-related allergy, and knowledge, at the molecular level, of this disorder is progressively accumulating. The aim of the present study is to investigate the panel of wheat IgE positivity in allergic Italian bakers, evaluating a possible contribution of novel wheat allergens included in the water/salt soluble fraction. The water/salt-soluble wheat flour proteins from the Italian wheat cultivar Bolero were separated by using 1-DE and 2-DE gel electrophoresis. IgE-binding proteins were detected using the pooled sera of 26 wheat allergic bakers by immunoblotting and directly recognized in Coomassie stained gel. After a preparative electrophoretic step, two enriched fractions were furtherly separated in 2-DE allowing for detection, by Coomassie, of three different proteins in the range of 21–27 kDa that were recognized by the pooled baker’s IgE. Recovered spots were analyzed by nanoHPLC Chip tandem mass spectrometry (MS/MS). The immunodetected spots in 2D were subjected to mass spectrometry (MS) analysis identifying two new allergenic proteins: a glucose/ribitol dehydrogenase and a 16.9 kDa class I heat shock protein 1. Mass spectrometer testing of flour proteins of the wheat cultivars utilized by allergic bakers improves the identification of until now unknown occupational wheat allergens.

Molecular characterization and transcriptional regulation of two types of H+-pyrophosphatases in the scuticociliate parasite Philasterides dicentrarchi

Proton-translocating inorganic pyrophosphatases (H⁺-PPases) are an ancient family of membrane bound enzymes that couple pyrophosphate (PPi) hydrolysis to H⁺ translocation across membranes. In this study, we conducted a molecular characterization of two isoenzymes (PdVP1 and PdVP2) located in respectively the alveolar sacs and in the membranes of the intracellular vacuoles of a scuticociliate parasite (Philasterides dicentrarchi) of farmed turbot. We analyzed the genetic expression of the isoenzymes after administration of antiparasitic drugs and after infection in the host. PdVP1 and PdVP2 are encoded by two genes of 2485 and 3069 bp, which respectively contain 3 and 11 exons and express proteins of 746 and 810 aa of molecular mass 78.9 and 87.6 kDa. Topological predictions from isoenzyme sequences indicate the formation of thirteen transmembrane regions (TMRs) for PdVP1 and seventeen TMRs for PdVP2. Protein structure modelling indicated that both isoenzymes are homodimeric, with three Mg²⁺ binding sites and an additional K⁺ binding site in PdVP2. The levels of identity and similarity between the isoenzyme sequences are respectively 33.5 and 51.2%. The molecular weights of the native proteins are 158 kDa (PdVP1) and 178 kDa (PdVP2). The isoenzyme sequences are derived from paralogous genes that form a monophyletic grouping with other ciliate species. Genetic expression of the isoenzymes is closely related to the acidification of alveolar sacs (PdVP1) and intracellular vacuoles (PdVP2): antiparasitic drugs inhibit transcription, while infection increases transcription of both isoenzymes. The study findings show that P. dicentrarchi possesses two isoenzymes with H⁺-PPase activity which are located in acidophilic cell compartment membranes and which are activated during infection in the host and are sensitive to antiparasitic drugs. The findings open the way to using molecular modelling to design drugs for the treatment of scuticociliatosis.

Cloning, purification, and characterization of inorganic pyrophosphatase from the hyperthermophilic archaea Pyrococcus horikoshii

The gene encoding inorganic pyrophosphatase (PPiase) from the hyperthermophilic archaea Pyrococcus horikoshii (Pho PPiase) was cloned in the Escherichia coli strain BL21/pET15b, and the recombinant PPiase was purified by Ni-chelating chromatography in only an one-step procedure. The PPiase showed optimal activity at 88°C and pH of 10.3. Kinetic analysis revealed Km, kcat, Vm of 14.27μM, 3436s(-1), and 34.35μmol/min/mg protein, respectively. Pho PPiase was stable against denaturant chemicals as well as heat. It retained 19.61% of the original activity after incubation at 100°C for 12h and 25.96% of the original activity in the presence of 8M urea after incubation at 50°C for 120h. Pho PPiase showed high specificity for inorganic pyrophosphate but low reactivity to sodium tripolyphosphate and sodium tetrapolyphosphate. ADP and ATP could not serve as substrates.

Energization of vacuolar transport in plant cells and its significance under stress

The plant vacuole is of prime importance in buffering environmental perturbations and in coping with abiotic stress caused by, for example, drought, salinity, cold, or UV. The large volume, the efficient integration in anterograde and retrograde vesicular trafficking, and the dynamic equipment with tonoplast transporters enable the vacuole to fulfill indispensible functions in cell biology, for example, transient and permanent storage, detoxification, recycling, pH and redox homeostasis, cell expansion, biotic defence, and cell death. This review first focuses on endomembrane dynamics and then summarizes the functions, assembly, and regulation of secretory and vacuolar proton pumps: (i) the vacuolar H(+)-ATPase (V-ATPase) which represents a multimeric complex of approximately 800 kDa, (ii) the vacuolar H(+)-pyrophosphatase, and (iii) the plasma membrane H(+)-ATPase. These primary proton pumps regulate the cytosolic pH and provide the driving force for secondary active transport. Carriers and ion channels modulate the proton motif force and catalyze uptake and vacuolar compartmentation of solutes and deposition of xenobiotics or secondary compounds such as flavonoids. ABC-type transporters directly energized by MgATP complement the transport portfolio that realizes the multiple functions in stress tolerance of plants.

Preparative isolation of protein complexes and other bioparticles by elution from polyacrylamide gels

Due to its unmatched resolution, gel electrophoresis is an indispensable tool for the analysis of diverse biomolecules. By adaptation of the electrophoretic conditions, even fragile protein complexes as parts of intracellular networks migrate through the gel matrix under sustainment of their integrity. If the thickness of such native gels is significantly increased compared to the analytical version, also high sample loads can be processed. However, the cage-like network obstructs an in-depth analysis for deciphering structure and function of protein complexes and other species. Consequently, the biomolecules have to be removed from the gel matrix into solution. Several approaches summarized in this review tackle this problem. While passive elution relies on diffusion processes, electroelution employs an electric field to force biomolecules out of the gel. An alternative procedure requires a special electrophoresis setup, the continuous elution device. In this apparatus, molecules migrate in the electric field until they leave the gel and were collected in a buffer stream. Successful isolation of diverse protein complexes like photosystems, ATP-dependent enzymes or active respiratory supercomplexes and some other bioparticles demonstrates the versatility of preparative electrophoresis. After liberating particles out of the gel cage, numerous applications are feasible. They include elucidation of the individual components up to high resolution structures of protein complexes. Therefore, preparative electrophoresis can complement standard purification methods and is in some cases superior to them.

Proton pumping inorganic pyrophosphatase of endoplasmic reticulum-enriched vesicles from etiolated mung bean seedlings

Endoplasmic reticulum (ER)-enriched vesicles from etiolated hypocotyls of mung bean seedlings (Vigna radiata) were successfully isolated using Ficoll gradient and two-phase (polyethylene glycol-dextran) partition. The ER-enriched vesicles contained inorganic pyrophosphate (PPi) hydrolysis and its associated proton translocating activities. Antiserum prepared against vacuolar H+-pyrophosphatase (V-PPase, EC 3.6.1.1) did not inhibit this novel pyrophosphatase-dependent proton translocation, excluding the possible contamination of tonoplast vesicles in the ER-enriched membrane preparation. The optimal ratios of Mg2+/PPi (inorganic pyrophosphate) for enzymatic activity and PPi-dependent proton translocation of ER-enriched vesicles were higher than those of vacuolar membranes. The PPi-dependent proton translocation of ER-enriched vesicles absolutely required the presence of monovalent cations with preference for K+, but could be inhibited by a common PPase inhibitor, F-. Furthermore, ER H+-pyrophosphatase exhibited some similarities and differences to vacuolar H+-PPases in cofactor/substrate ratios, pH profile, and concentration dependence of F-, imidodiphosphate (a PPi analogue), and various chemical modifiers. These results suggest that ER-enriched vesicles contain a novel type of proton-translocating PPase distinct from that of tonoplast from higher plants.

The β-subunit of pea stem mitochondrial ATP synthase exhibits PPiase activity

A soluble protein with a molecular mass of 55 kDa has been purified from etiolated pea stem mitochondria. The protein exhibits a Mg2+-requiring PPiase activity, with an optimum at pH 9.0, which is not stimulated by monovalent cations, but inhibited by F-, Ca2+, aminomethylenediphosphate and imidodiphosphate. The protein does not cross-react with polyclonal antibodies raised against vacuolar, mitochondrial or soluble PPiases, respectively. Conversely, it cross-reacts with an antibody for the alpha/beta-subunit of the ATP synthase from beef heart mitochondria. The purified protein has been analyzed by MALDI-TOF mass spectrometry and the results, covering the 30% of assigned sequence, indicate that it corresponds to the beta-subunit of the ATP synthase of pea mitochondria. It is suggested that this enzymatic protein may perform a dual function as soluble PPiase or as subunit of the more complex ATP synthase.

Further development of an electroosmotic medium pump system for preparative disk gel electrophoresis

A simple and practical 6.8-cm-diameter (36.30-cm(2) cross-sectional-area) preparative disk gel electrophoresis device, based on the design of M. Hayakawa et al. (Anal. Biochem. 288 (2001) 168), in which the elution buffer is driven by an electroosmotic buffer flow through the membrane into the elution chamber from the anode chamber was constructed. We have found that the dialysis membranes employed provide suitable flow rates for the elution buffer, similar to those of an earlier 3.6-cm-diameter device, resulting in the prevention of excess eluate dilution. The efficiency of this device was demonstrated by the fractionation of a bovine serum albumin (BSA) Cohn V fraction into monomer, dimer, and oligomer components using nondenaturing polyacrylamide gel electrophoresis (native-PAGE). The maximum protein concentration of the eluate achieved was 133 mg/ml of BSA monomer, which required a dilution of the eluate for subsequent analytical PAGE performance. As a practical example, the two-dimensional fractionation of soluble dipeptidyl peptidase IV (sDPP IV) from 50 ml fetal bovine serum (3.20 g protein) per gel is presented. The sDPP IV enzyme protein was recovered in a relatively short time, utilizing a 6.5% T native-PAGE and subsequential sodium dodecyl sulfate-PAGE system. This device enhances the possibility of continuous electrophoretic fractionation of complex protein mixtures on a preparative scale.

Pyrophosphate import and synthesis by plant mitochondria

The matrix level of pyrophosphate (PPi) in mitochondria isolated from etiolated pea (Pisum sativum L. cv. Alaska) stems was evaluated, on the basis of an enzymatic assay, to be approx. 0.2 mM. Pyrophosphate could enter from the cytoplasm to the mitochondria via adenine nucleotide translocase (ANT), because F- and Ca2+ (two penetrating PPiase inhibitors) and atractylate (ANT inhibitor) inhibited PPiase activity in isolated mitochondria supplied with PPi. This result was also confirmed by measuring oxygen consumption and membrane potential (DeltaPsi) in succinate-energized mitochondria. In a medium free of phosphate (Pi), the addition of PPi before the substrate rendered possible an ADP-stimulated oxygen consumption that was inhibited by F- or Ca2+. In a similar experiment, ADP induced the dissipation of DeltaPsi when it was added after the succinate-generated DeltaPsi had reached a steady state and, again, F- inhibited this dissipation. These results imply that PPi enters the mitochondria where it is hydrolyzed to 2 Pi which become available for the H+-ATPase (EC 3.6.1.34). In addition, PPi may be synthesized by the H+-PPiase (EC 3.6.1.1), acting as a synthase. This evidence arises from the observation that Pi stimulated an oxygen consumption (respiratory control ratio of 1.7) that was inhibited by F- or Ca2+. The physiological role of the mitochondrial H+-PPiase is discussed in the light of the consideration that this enzyme can catalyse a readily reversible reaction.

Novel type Arabidopsis thaliana H(+)-PPase is localized to the Golgi apparatus

Vacuolar H(+)-PPase, a membrane bound proton-translocating pyrophosphatase found in various species including plants, some protozoan and prokaryotes, has been demonstrated to be localized to the vacuolar membrane in plants. Using a GUS reporter system and a green fluorescent protein (GFP) fusion protein, we investigated the tissue distribution and the subcellular localization, respectively, of a novel type H(+)-PPase encoded by AVP2/AVPL1 identified in the Arabidopsis thaliana genome. We showed that AVP2/AVPL1 is highly expressed at the trichome and the filament of stamen. Furthermore, the fluorescence of GFP-tagged AVP2/AVPL1 showed small dot-like structures that were observed throughout the cytoplasm of various Arabidopsis cells under a fluorescent microscope. The distribution of this dot-like fluorescent pattern was apparently affected by a treatment with brefeldin A. Moreover, we demonstrated that most dot-like fluorescent structures colocalized with a Golgi resident protein. These findings suggest that this novel type H(+)-PPase resides on the Golgi apparatus rather than the vacuolar membrane.

AVP2, a sequence-divergent, K(+)-insensitive H(+)-translocating inorganic pyrophosphatase from Arabidopsis

Plant vacuolar H(+)-translocating inorganic pyrophosphatases (V-PPases; EC 3.6.1.1) have been considered to constitute a family of functionally and structurally monotonous intrinsic membrane proteins. Typified by AVP1 (V. Sarafian, Y. Kim, R.J. Poole, P.A. Rea [1992] Proc Natl Acad Sci USA 89: 1775-1779) from Arabidopsis, all characterized plant V-PPases share greater than 84% sequence identity and catalyze K(+)-stimulated H(+) translocation. Here we describe the molecular and biochemical characterization of AVP2 (accession no. AF182813), a sequence-divergent (36% identical) K(+)-insensitive, Ca(2+)-hypersensitive V-PPase active in both inorganic pyrophosphate hydrolysis and H(+) translocation. The differences between AVP2 and AVP1 provide the first indication that plant V-PPases from the same organism fall into two distinct categories. Phylogenetic analyses of these and other V-PPase sequences extend this principle by showing that AVP2, rather than being an isoform of AVP1, is but one representative of a novel category of AVP2-like (type II) V-PPases that coexist with AVP1-like (type I) V-PPases not only in plants, but also in apicomplexan protists such as the malarial parasite Plasmodium falciparum.

Vacuolar H(+)-pyrophosphatase

The H(+)-translocating inorganic pyrophosphatase (H(+)-PPase) is a unique, electrogenic proton pump distributed among most land plants, but only some alga, protozoa, bacteria, and archaebacteria. This enzyme is a fine model for research on the coupling mechanism between the pyrophosphate hydrolysis and the active proton transport, since the enzyme consists of a single polypeptide with a calculated molecular mass of 71-80 kDa and its substrate is also simple. Cloning of the H(+)-PPase genes from several organisms has revealed the conserved regions that may be the catalytic site and/or participate in the enzymatic function. The primary sequences are reviewed with reference to biochemical properties of the enzyme, such as the requirement of Mg(2)(+) and K(+). In plant cells, H(+)-PPase coexists with H(+)-ATPase in a single vacuolar membrane. The physiological significance and the regulation of the gene expression of H(+)-PPase are also reviewed.

Radiation inactivation analysis of H(+)-pyrophosphatase from submitochondrial particles of etiolated mung bean seedlings

Radiation inactivation analysis was employed to determine the functional masses of enzymatic activity and proton translocation of H(+)-pyrophosphatase from submitochondrial particles of etiolated mung bean seedlings. The activities of H(+)-pyrophosphatase decayed as a simple exponential function with respect to radiation dosage. D(37) values of 6.9+/-0.3 and 7.5+/-0.5 Mrad were obtained for pyrophosphate hydrolysis and its associated proton translocation, yielding molecular masses of 170+/-7 and 156+/-11 kDa, respectively. In the presence of valinomycin and 50 mM KCl, the functional size of H(+)-pyrophosphatase of tonoplast was decreased, while that of submitochondrial particles remained the same, indicating that they are two distinct types of proton pump using PP(i) as their energy source.

The detection of enzyme activity following sodium dodecyl sulfate-polyacrylamide gel electrophoresis

More than a hundred different enzymes impinging on aspects of cell function ranging from carbohydrate and lipid metabolism to signal transduction and gene expression to biomolecule degradation have been detected by the assay of their enzymatic activities following SDS-PAGE. The strategies by which this has been accomplished are as varied as the enzymes themselves and offer testimony to the creativeness and ingenuity of life scientists. Assay of enzyme activity following SDS-PAGE is well adapted to identifying the source of catalytic activity in a heterogeneous protein mixture or a heterooligomeric protein (20), or determining if multiple catalytic activities reside in a single polypeptide (60). The alliance of versatile enzyme assay techniques with the molecular resolution of SDS-PAGE offers a powerful means for meeting the increasing demand for the high-throughput screening arising from protein engineering, combinatorial chemistry, and functional genomics.

Purification and characterization of thylakoid membrane-bound inorganic pyrophosphatase from Spinacia oleracia L

An inorganic pyrophosphatase (PPase) was purified from thylakoid membrane of spinach leaves to electrophoretic purity by methods including detergent solubilization, ammonium sulfate fractionation, and successive chromatographic techniques. Current protocol yielded about 10% recovery of total activity with a 30-fold purification. The specific activity of the purified enzyme was approximately 400 micromol PPi consumed/mg protein x h. This enzyme is a monomer with a molecular mass of 55 kDa. Several properties, including subunit composition, substrate specificity, ion requirements, inhibitor sensitivities, and amino acid composition, have been studied. Mg2+ is an essential cofactor for the thylakoid PPase. The preferred substrate for the hydrolytic reaction of PPase appears to be dimagnesium pyrophosphate. K+ could not stimulate the enzymatic activity of thylakoid PPase, while F- was a potent inhibitor. Group-specific modification of the thylakoid PPase demonstrates possible involvement of carboxylate residues in the enzymatic activity. Furthermore, antibodies raised against thylakoid PPase in a rabbit could inactivate the PPi hydrolysis of thylakoid and the purified enzyme, but not that of vacuolar H+-PPase, indicating both PPi hydrolases are structurally distinct.