Identification and characterisation of the IgE-binding proteins 2S albumin and conglutin gamma in almond (Prunus dulcis) seeds.

BACKGROUND: Almond proteins can cause severe anaphylactic reactions in susceptible individuals. The aim of this study was the identification of IgE-binding proteins in almonds and the characterisation of these proteins by N-terminal sequencing. METHODS: Five sera were selected from individuals with a positive reaction to food challenge. Sodium dodecylsulphate-polyacrylamide gel electrophoresis and immunoblotting were performed on almond seed proteins. Purified IgE-binding proteins were tested for immunoblot inhibition with sera pre-incubated with extracts of hazelnut and walnut. RESULTS: N-terminal sequences of the 12-, 30- and 45-kD proteins were obtained. The 45- and 30-kD proteins shared the same N terminus, with 60% homology to the conglutin gamma heavy chain from lupine seed (Lupinus albus) and to basic 7S globulin from soybean (Glycine max). The sequences of the N-terminal 12-kD protein and of an internal peptide obtained by endoproteinase digestion showed good homology to 2S albumin from English walnut (Jug r 1). Immunoblot inhibition experiments were performed and IgE binding to almond 2S albumin and conglutin gamma was detected in the presence of cross-reacting walnut or hazelnut antigens. CONCLUSIONS: Two IgE-binding almond proteins were N-terminally sequenced and identified as almond 2S albumin and conglutin gamma. Localisation and conservation of IgE binding in a 6-kD peptide obtained by endoproteinase digestion of 2S albumin was shown.

Cell cycle-dependent interaction of Mad2 with conserved Box1/2 region of human granulocyte-macrophage colony-stimulating factor receptor common betac.

Box1 and 2 (box1/2) are conserved cytoplasmic motifs located in the membrane proximal region of cytokine receptors, including the human granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor common betac. Deletion of box1/2 abrogated all the examined activities of GM-CSF, and this phenomenon is explained by the loss of binding by Jak2. To test if a molecule other than Jak2 interacting with the box1/2 region plays a role in GM-CSF receptor signal transduction, we screened for molecules interacting with the box1/2 region by a pull-down assay using recombinant purified protein of GST fused with the betac box1/2 region and a Ba/F3 cell lysate. The mouse homologue of Mad2 protein, which plays an important role in the M phase of the cell cycle, was revealed to associate with the box1/2 region specifically. Peptides corresponding to the box1 sequence also bound to Mad2, and mutation of the box1 decreased the Mad2 interaction. Deletion analysis indicated that interaction with box1/2 occurred through the C-terminal portion of Mad2. Mad2 is known to change affinity for binding partners cell cycle dependently. Binding affinity of Mad2 to box1/2 increased in the late M phase, suggesting the possibility that GM-CSF participates in regulation of the M phase check point through interaction with Mad2.

Molecular characterization and gene expression of lhcb5 gene encoding CP26 in the light-harvesting complex II of Chlamydomonas reinhardtii.

We isolated and sequenced a cDNA clone encoding a minor chlorophyll a/b-binding protein, CP26, which is associated with the light-harvesting complex II of Chlamydomonas reinhardtii. Protein sequences of internal peptide fragments from purified CP26 were determined and used to identify a cDNA clone. The 1.1 kb lhcb5 gene codes for a polypeptide of 289 amino acids with a predicted molecular weight of 30,713. The lhcb5 gene product could reconstitute with chlorophylls and xanthophylls to form a green band on a gel. Although the expression of many lhcb genes are strictly regulated by light, the lhcb5 gene was only loosely regulated. We propose that a plant acclimatizes itself to the light environment by quantitatively and qualitatively modulating the light-harvesting complex. Characterization of the primary structure and the implications of its unique expression are discussed.

Distinct intramembrane cleavage of the beta-amyloid precursor protein family resembling gamma-secretase-like cleavage of Notch.

The intramembrane cleavage of beta-amyloid precursor protein by gamma-secretase is the final step in the generation of amyloid beta-protein. A 59- or 57-residue C-terminal fragment called CTFgamma is produced concomitantly. Putative CTFgamma generated in rat brain membrane preparations was purified and sequenced. Instead of CTFgamma, shorter 50- and 49-residue fragments were identified. In addition, we found similar C-terminal fragments of beta-amyloid precursor-like proteins 1 and 2; these were also cleaved at corresponding sites. This newly identified cleavage occurs at a site two to five residues inside the cytoplasmic membrane boundary, which is very similar to gamma-secretase-like cleavage of Notch 1.

Stage-specific modification of G protein beta subunits in rat placenta.

We previously analysed the plasma membrane proteins of rat placenta and prepared a database of 150 plasma membrane proteins, expressed in a stage-specific manner, utilizing two-dimensional gel electrophoresis (2D/E) [Mol. Cell. Endocrinol. 115(1995)149]. In this study, we focused on the proteins, tentatively named psL-I (MW 36.2 kDa, pI 5.3) and psL-II (35.9 kDa, 5.3), which were expressed mainly in late pregnancy. Close to psL-I and psL-II on 2D/E gels, we also recognized more abundant proteins [psC-I (36.2 kDa, 5.4) and psC-II (35.9 kDa, 5.4), respectively] arranged side by side with the same MW but different pI. Expression of psL-I and psL-II was detected only in junctional zone of placenta, whereas psC-I and psC-II were expressed in both labyrinth and junctional zones. In addition, psL-I and psL-II began to increase on day 16 of pregnancy and peaked at term, whereas expression of psC-I and psC-II was relatively constant. The analysis of these four proteins (psL-I, psL-II, psC-I and psC-II) by preparative 2D/E, peptide mapping, amino acid sequence and mass spectrometry (MALDI-TOF-MS) revealed that psC-I was a G protein beta1 subunit, and psC-II was a beta2 subunit, and showed that psL-I and psL-II were molecular modified forms of psC-I and psC-II, respectively. Expression of these G protein beta subunits (psL-I, psL-II, psC-I and psC-II) was also observed in rat choriocarcinoma cells, Rcho-1 cells. Expression of psC-I and psC-II was much higher than those of psL-I and psL-II, and their level was relatively constant regardless of the stage of differentiation in vitro. Interestingly, expression of psL-I and psL-II gradually increased in association with the differentiation. Since the expression of beta1 and beta2 subunit proteins and their mRNAs was constant during the process of differentiation in Rcho-1 cells, the expression of these lower pI forms of G protein subunits (psL-I and psL-II) was thought to be post-translationally regulated. In conclusion, there are modified forms of G protein beta1 and beta2 subunits, in the placenta and Rcho-1 cells, which are expressed in a pregnancy-stage or differentiation stage specific manner.

Serine proteinase inhibitor 3 and murinoglobulin I are potent inhibitors of neuropsin in adult mouse brain.

Extracellular serine protease neuropsin (NP) is expressed in the forebrain limbic area of adult brain and is implicated in synaptic plasticity. We screened for endogenous NP inhibitors with recombinant NP (r-NP) from extracts of the hippocampus and the cerebral cortex in adult mouse brain. Two SDS-stable complexes were detected, and after their purification, peptide sequences were determined by amino acid sequencing and mass spectrometry, revealing that target molecules were serine proteinase inhibitor-3 (SPI3) and murinoglobulin I (MUG I). The addition of the recombinant SPI3 to r-NP resulted in an SDS-stable complex, and the complex formation followed bimolecular kinetics with an association rate constant of 3.4 +/- 0.22 x 10(6) M(-1) s(-1), showing that SPI3 was a slow, tight binding inhibitor of NP. In situ hybridization histochemistry showed that SPI3 mRNA was expressed in pyramidal neurons in the hippocampal CA1-CA3 subfields, as was NP mRNA. Alternatively, the addition of purified plasma MUG I to r-NP resulted in an SDS-stable complex, and MUG I inhibited degradation of fibronectin by r-NP to 24% at a r-NP/MUG I molar ratio of 1:2. Immunofluorescence histochemistry showed that MUG I localized in the hippocampal neurons. These findings indicate that SPI3 and MUG I serve to inactivate NP and control the level of NP in adult brain, respectively.

Supernatant protein factor, which stimulates the conversion of squalene to lanosterol, is a cytosolic squalene transfer protein and enhances cholesterol biosynthesis.

Squalene epoxidase, a membrane-associated enzyme that converts squalene to squalene 2,3-oxide, plays an important role in the maintenance of cholesterol homeostasis. In 1957, Bloch and colleagues identified a factor from rat liver cytosol termed "supernatant protein factor (SPF)," which promotes the squalene epoxidation catalyzed by rat liver microsomes with oxygen, NADPH, FAD, and phospholipid [Tchen, T. T. & Bloch, K. (1957) J. Biol. Chem. 226, 921-930]. Although purification of SPF by 11,000-fold was reported, no information is so far available on the primary structure or biological function of SPF. Here we report the cDNA cloning and expression of SPF from rat and human. The encoded protein of 403 amino acids belongs to a family of cytosolic lipid-binding/transfer proteins such as alpha-tocopherol transfer protein, cellular retinal binding protein, yeast phosphatidylinositol transfer protein (Sec14p), and squid retinal binding protein. Recombinant SPF produced in Escherichia coli enhances microsomal squalene epoxidase activity and promotes intermembrane transfer of squalene in vitro. SPF mRNA is expressed abundantly in the liver and small intestine, both of which are important sites of cholesterol biosynthesis. SPF is expressed significantly in isolated hepatocytes, but the expression level was markedly decreased after 48 h of in vitro culture. Moreover, SPF was not detectable in most of the cell lines tested, including HepG2 and McARH7777 hepatomas. Transfection of SPF cDNA in McARH7777 significantly stimulated de novo cholesterol biosynthesis. These data suggest that SPF is a cytosolic squalene transfer protein capable of regulating cholesterol biosynthesis.

Gene cloning, expression, crystallization and preliminary X-ray analysis of Thermus thermophilus arginyl-tRNA synthetase.

The gene encoding the highly thermostable arginyl-tRNA synthetase (ArgRS) from Thermus thermophilus was cloned and overexpressed in Escherichia coli under the control of the T7 promoter. The recombinant ArgRS was purified by two chromatographic steps and was crystallized by the hanging-drop vapour-diffusion method using PEG 8000 and ethylene glycol as precipitants. The crystals belong to the hexagonal space group P6(5), with unit-cell parameters a = b = 156.04 (7), c = 87.17 (4) A. X-ray data to 2.8 A resolution were collected at room temperature from a native crystal using an in-house X-ray source. Uranium, platinum and selenomethionine derivatives were found to be useful for phasing by the multiple isomorphous replacement method with anomalous scattering. The flash-frozen crystals diffracted beyond 2.3 A resolution using synchrotron radiation from the beamline 41XU at SPring-8 (Harima).

A novel motor, KIF13A, transports mannose-6-phosphate receptor to plasma membrane through direct interaction with AP-1 complex.

Intracellular transport mediated by kinesin superfamily proteins (KIFs) is a highly regulated process. The molecular mechanism of KIFs binding to their respective cargoes remains unclear. We report that KIF13A is a novel plus end-directed microtubule-dependent motor protein and associates with beta 1-adaptin, a subunit of the AP-1 adaptor complex. The cargo vesicles of KIF13A contained AP-1 and mannnose-6-phosphate receptor (M6PR). Overexpression of KIF13A resulted in mislocalization of the AP-1 and the M6PR. Functional blockade of KIF13A reduced cell surface expression of the M6PR. Thus, KIF13A transports M6PR-containing vesicles and targets the M6PR from TGN to the plasma membrane via direct interaction with the AP-1 adaptor complex.

CIRP2, a major cytoplasmic RNA-binding protein in Xenopus oocytes.

In an attempt to isolate mRNA-binding proteins we fractionated Xenopus oocyte lysate by oligo(dT)-cellulose chromatography. A 20 kDa protein was the major component of the eluate. cDNA cloning revealed that this protein is a Xenopus homolog of the cold-inducible RNA-binding protein (CIRP) which was originally identified in mammalian cells as a protein that is overexpressed upon a temperature downshift. This Xenopus protein, termed here xCIRP2, is highly expressed in ovary, testis and brain in adult Xenopus tissues. In oocytes it is predominantly localized in the cytoplasm. By biochemical fractionation we provide evidence that xCIRP2 is associated with ribosomes, suggesting that it participates in translational regulation in oocytes. Microinjection of labeled mRNA into oocytes followed by UV cross-linking of the oocyte lysate led to identification of two major RNA-binding activities. Immunoprecipitation of the RNA-binding proteins demonstrated that one is xCIRP2 and that the other contains FRGY2. FRGY2, which is one of the principal constituents of mRNA storage particles involved in translational masking of maternal mRNA, has an RNA-binding domain conserved to those of bacterial cold shock proteins. Possible implications of the highly abundant expression in oocytes of cold shock RNA-binding proteins of both eukaryotic and prokaryotic types are discussed.

Molecular cloning and expression of cDNA encoding chicken UDP-N-acetyl-D-glucosamine (GlcNAc): GlcNAcbeta 1-6(GlcNAcbeta 1-2)- manalpha 1-R[GlcNAc to man]beta 1,4N-acetylglucosaminyltransferase VI.

A cDNA that encodes UDP-N-acetyl-d-glucosamine (GlcNAc):GlcNAcbeta1-6(GlcNAcbeta1-2)Manalpha1-R[GlcNA c to Man]beta1, 4N-acetylglucosaminyltransferase VI (GnT VI), which is responsible for the formation of pentaantennary asparagine-linked oligosaccharides (N-glycans), has been cloned from a hen oviduct cDNA library based on the partial amino acid sequences of the purified enzyme. The isolated cDNA clone contained an open reading frame encoding 464 amino acids, including all of the peptides that were sequenced. The deduced amino acid sequence predicts a type II transmembrane topology and contains two potential N-glycosylation sites. The primary structure was found to be significantly similar to human GnT IV-homologue, the gene for which was cloned from the deleted region in pancreatic cancer, and to human and bovine GnT IVs. Chicken GnT VI-transfected COS-1 cells showed a high GnT VI activity (26.8 pmol/h/mg protein), whereas nontransfected, mock-transfected, or human GnT IV-homologue-transfected COS-1 cells had no activity. Northern blot analysis using poly(A)(+) RNA from hen oviduct indicated that the size of GnT VI mRNA is 2.1 kilobases. Reverse transcription-polymerase chain reaction analysis showed that GnT VI mRNA was relatively highly expressed in oviduct, spleen, lung, and colon.

Interactions of a didomain fragment of the Drosophila sex-lethal protein with single-stranded uridine-rich oligoribonucleotides derived from the transformer and Sex-lethal messenger RNA precursors: NMR with residue-selective [5-2H]uridine substitutions.

Proteins that contain two or more copies of the RNA-binding domain [ribonucleoprotein (RNP) domain or RNA recognition motif (RRM)] are considered to be involved in the recognition of single-stranded RNA, but the mechanisms of this recognition are poorly understood at the molecular level. For an NMR analysis of a single-stranded RNA complexed with a multi-RBD protein, residue-selective stable-isotope labeling techniques are necessary, rather than common assignment methods based on the secondary structure of RNA. In the present study, we analyzed the interaction of a Drosophila Sex-lethal (Sx1) protein fragment, consisting of two RBDs (RBD1-RBD2), with two distinct target RNAs derived from the tra and Sxl mRNA precursors with guanosine and adenosine, respectively, in a position near the 5'-terminus of a uridine stretch. First, we prepared a [5-2H]uridine phosphoramidite, and synthesized a series of 2H-labeled RNAs, in which all of the uridine residues except one were replaced by [5-2H]uridine in the target sequence, GU8C. By observing the H5-H6 TOCSY cross peaks of the series of 2H-labeled RNAs complexed with the Sx1 RBDI-RBD2, all of the base H5-H6 proton resonances of the target RNA were unambiguously assigned. Then, the H5-H6 cross peaks of other target RNAs, GU2GU8, AU8, and UAU8, were assigned by comparison with those of GU8C. We found that the uridine residue prior to the G or A residue is essential for proper interaction with the protein, and that the interaction is tighter for A than for G. Moreover, the H1' resonance assignments were achieved from the H5-H6 assignments. The results revealed that all of the protein-bound nucleotide residues, except for only two, are in the unusual C2'-endo ribose conformation in the complex.

Identification of a PDZ-domain-containing protein that interacts with the scavenger receptor class B type I.

The scavenger receptor class B type I (SR-BI) mediates the selective uptake of cholesteryl esters from high-density lipoprotein (HDL) and cholesterol secretion into bile in the liver. In this study, we identified an SR-BI-associated protein from rat liver membrane extracts by using an affinity chromatography technique. This protein of 523 amino acids contains four PDZ domains and associates with the C terminus of SR-BI by using its N-terminal first PDZ domain. Therefore, we denoted this protein as CLAMP (C-terminal linking and modulating protein). CLAMP was located mostly in the sinusoidal membranes, whereas SR-BI was detected in both sinusoidal and canalicular membranes. After the solubilization of the liver membranes with Triton X-100, SR-BI was immunoprecipitated with anti-CLAMP monoclonal antibody, suggesting the association of these proteins in vivo. By coexpressing SR-BI with CLAMP in Chinese hamster ovary cells, we observed (i) the increase in the expression level of SR-BI, (ii) the reduction in the deacylation rate of the cholesteryl esters taken up from HDL, and (iii) the change in the intracellular distribution of fluorescent lipid 1,1'-dioctadecyl-3,3, 3',3'-tetramethylindocarbocyanine percholate taken up from HDL. Taken together, these data suggest that CLAMP, a four-PDZ-domain-containing protein, is associated with SR-BI in the liver sinusoidal plasma membranes and may modulate the intracellular transport and metabolism of cholesteryl esters taken up from HDL.

Post-translational modification is essential for catalytic activity of nitrile hydratase.

Nitrile hydratase from Rhodococcus sp. N-771 is an alphabeta heterodimer with a nonheme ferric iron in the catalytic center. In the catalytic center, alphaCys112 and alphaCys114 are modified to a cysteine sulfinic acid (Cys-SO2H) and a cysteine sulfenic acid (Cys-SOH), respectively. To understand the function and the biogenic mechanism of these modified residues, we reconstituted the nitrile hydratase from recombinant unmodified subunits. The alphabeta complex reconstituted under argon exhibited no activity. However, it gradually gained the enzymatic activity through aerobic incubation. ESI-LC/MS analysis showed that the anaerobically reconstituted alphabeta complex did not have the modification of alphaCys112-SO2H and aerobic incubation induced the modification. The activity of the reconstituted alphabeta complex correlated with the amount of alphaCys112-SO2H. Furthermore, ESI-LC/MS analyses of the tryptic digest of the reconstituted complex, removed of ferric iron at low pH and carboxamidomethylated without reduction, suggested that alphaCys114 is modified to Cys-SOH together with the sulfinic acid modification of alphaCys112. These results suggest that alphaCys112 and alphaCys114 are spontaneously oxidized to Cys-SO2H and Cys-SOH, respectively, and alphaCys112-SO2H is responsible for the catalytic activity solely or in combination with alphaCys114-SOH.

Characterization of a novel fungal protein, p15, which induces neuronal differentiation of PC12 cells.

In our previous paper, we reported that a 15 kDa protein (p15) produced by a fungus, genus Helicosporium, enhanced NGF-induced neurite outgrowth from PC12 cells. Here we further characterized the actions of p15. The complete amino acid sequence of p15 was determined and it was shown to be a hydrophilic protein composed of 118 amino acid residues with two intramolecular disulfide bridges. p15-induced neurite outgrowth was blocked by the depletion of extracellular Ca(2+) in the culture medium and was significantly inhibited by L-type Ca(2+) channel inhibitor nicardipine. p15 stimulated Src kinase and MAPK activities, and neurite outgrowth was not observed in srcDN2, a dominant negative c-src(K295R)-expressing cell line, and was significantly reduced in RasN17-expressing cells. These results suggest that p15 stimulates neurite outgrowth through the potentiation of L-type Ca(2+) channels, thereby activating the Src-Ras-MAPK cascade.

The relationship between ST6Gal I Golgi retention and its cleavage-secretion.

The ST6Gal I is a sialyltransferase that modifies N-linked oligosaccharides of glycoproteins. Previous results suggested a role for luminal stem and active domain sequences in the efficiency of ST6Gal I Golgi retention. Characterization of a series of STtyr isoform deletion mutants demonstrated that the stem is sensitive to proteases and that preventing cleavage in this region leads to increased cell surface expression. A mutant lacking amino acids 32-104 (STDelta4) is not active or cleaved and secreted like the wild type STtyr, but does exhibit increased cell surface expression. It is probable that the STDelta4 mutant lacks the stem region and some amino acids of the active domain because the STDelta5 mutant lacking amino acids 86-104 is also not active but is cleaved and secreted. In contrast, deletion of stem amino acids between residues 32 and 86 in the STDelta1, STDelta2, and STDelta3 mutants does not inactive these enzyme forms, eliminate their cleavage and secretion, or increase their cell surface expression. Surprisingly, cleavage occurs even though the previously identified Asn63-Ser 64 cleavage site is missing. Further evaluation demonstrated that a cleavage site between Lys 40 and Glu 41 is used in COS cells. Mutagenesis of Lys 40 significantly decreased, but did not eliminate cleavage, suggesting that there are additional secondary sites of cleavage in the ST6Gal I stem.

An automated interpretation of MALDI/TOF postsource decay spectra of oligosaccharides. 1. Automated peak assignment.

A computer program has been developed that helps the interpretation of MALDI/TOF postsource decay (PSD) spectra of N-linked oligosaccharides of a protein. The program includes routines for automated peak assignment and generation of a simulated PSD spectrum. From a raw spectrum, peaks are assigned automatically; i.e., numbers of saccharide residues removed from the parent ion are calculated. If the structure of the oligosaccharide is known, a simulated PSD spectrum of the oligosaccharide will be generated. The simulated PSD spectrum helps interpretation of the observed spectrum. While, in a case where several candidate structures are given, one can narrow the field of plausible structures for the unknown oligosaccharide by comparing the observed spectrum with the simulated PSD spectra. Using a Pentium 233-MHz microprocessor, it takes only a few seconds to interpret a spectrum.

Fission yeast condensin complex: essential roles of non-SMC subunits for condensation and Cdc2 phosphorylation of Cut3/SMC4.

The condensin complex in frog extracts, containing two SMC (structural maintenance of chromosomes) and three non-SMC subunits, promotes mitotic chromosome condensation, and its supercoiling activity increases during mitosis by Cdc2 phosphorylation. Here, we report that fission yeast has the same five-member condensin complex, each of which is essential for mitotic condensation. The condensin complex was purified and the subunits were identified by microsequencing. Cnd1, Cnd2, and Cnd3, three non-SMC subunits showing a high degree of sequence conservation to frog subunits, are essential for viability, and their gene disruption leads to a phenotype indistinguishable from that observed in cut3-477 and cut14-208, known mutations in SMC4 and SMC2-like subunits. Condensin subunits tagged with GFP were observed to alter dramatically their localization during the cell cycle, enriched in the nucleus during mitosis, but cytoplasmic during other stages. This stage-specific alteration in localization requires mitosis-specific phosphorylation of the T19 Cdc2 site in Cut3. The T19 site is phosphorylated in vitro by Cdc2 kinase and shows the maximal phosphorylation in metaphase in vivo. Its alanine substitution mutant fails to suppress the temperature-sensitive phenotype of cut3-477, and shows deficiency in condensation, probably because Cut3 T19A remains cytoplasmic. Therefore, direct Cdc2 phosphorylation of fission yeast condensin may facilitate its nuclear accumulation during mitosis.

Tertiary and quaternary structures of photoreactive Fe-type nitrile hydratase from Rhodococcus sp. N-771: roles of hydration water molecules in stabilizing the structures and the structural origin of the substrate specificity of the enzyme.

The crystal structure analysis of the Fe-type nitrile hydratase from Rhodococcus sp. N-771 revealed the unique structure of the enzyme composed of the alpha- and beta-subunits and the unprecedented structure of the non-heme iron active center [Nagashima, S., et al. (1998) Nat. Struct. Biol. 5, 347-351]. A number of hydration water molecules were identified both in the interior and at the exterior of the enzyme. The study presented here investigated the roles of the hydration water molecules in stabilizing the tertiary and the quaternary structures of the enzyme, based on the crystal structure and the results from a laser light scattering experiment for the enzyme in solution. Seventy-six hydration water molecules between the two subunits significantly contribute to the alphabeta heterodimer formation by making up the surface shape, forming extensive networks of hydrogen bonds, and moderating the surface charge of the beta-subunit. In particular, 20 hydration water molecules form the extensive networks of hydrogen bonds stabilizing the unique structure of the active center. The amino acid residues hydrogen-bonded to those hydration water molecules are highly conserved among all known nitrile hydratases and even in the homologous enzyme, thiocyanate hydrolase, suggesting the structural conservation of the water molecules in the NHase family. The crystallographic asymmetric unit contained two heterodimers connected by 50 hydration water molecules. The heterotetramer formation in crystallization was clearly explained by the concentration-dependent aggregation state of NHase found in the light scattering measurement. The measurement proved that the dimer-tetramer equilibrium shifted toward the heterotetramer dominant state in the concentration range of 10(-2)-1.0 mg/mL. In the tetramer dominant state, 50 water molecules likely glue the two heterodimers together as observed in the crystal structure. Because NHase exhibits a high abundance in bacterial cells, the result suggests that the heterotetramer is physiologically relevant. In addition, it was revealed that the substrate specificity of this enzyme, recognizing small aliphatic substrates rather than aromatic ones, came from the narrowness of the entrance channel from the bulk solvent to the active center. This finding may give a clue for changing the substrate specificity of the enzyme. Under the crystallization condition described here, one 1,4-dioxane molecule plugged the channel. Through spectroscopic and crystallographic experiments, we found that the molecule prevented the dissociation of the endogenous NO molecule from the active center even when the crystal was exposed to light.

Production of homo- and hetero-dimeric isozymes from two aldehyde oxidase genes of Arabidopsis thaliana.

Polyclonal antibodies were raised against synthetic peptides or recombinant polypeptides encoded by Arabidopsis atAO-1 and atAO-2 cDNAs, which have sequences similar to maize and animal aldehyde oxidase (AO) cDNAs. Anti-atAO-1 antibodies recognized AOalpha and AObeta among the three isoforms, AOalpha, AObeta, and AOgamma, detected in Arabidopsis seedlings after native PAGE, while anti-atAO-2 antibodies reacted with AObeta and AOgamma. The polypeptide specifically recognized by each antibody was collected as the Protein-A/IgG/antigen complex. The 150- and 145-kDa polypeptides were purified by SDS-PAGE and digested with Achromobacter Protease I. From the amino acid sequences and molecular masses of the derivative peptides, it was revealed that the 150- and 145-kDa polypeptides were the products of atAO-1 and atAO-2, respectively. Molecular masses of the native forms of AOalpha, AObeta, and AOgamma were estimated as approximately 290-300 kDa. These results suggest that AOalpha and AOgamma are homodimers consisting of atAO-1 and atAO-2 products, respectively, and that AObeta is a heterodimer of the atAO-1 and atAO-2 products.