Identification of Chitinase and Osmotin-Like Protein as Actin-Binding Proteins in Suspension-Cultured Potato Cells

Cytoplasmic aggregation is an early resistance-associated eventthat is observed in potato tissues either after penetrationof an incompatible race of Phytophthora infestans, the potatolate blight fungus, or after treatment with hyphal wall components(HWC) prepared from P. infestans. In potato cells in suspensionculture, the number of cells with cytoplasmic aggregation increasedupon treatment with HWC, but such an increase was suppressedby treatment with cytochalasin D prior to treatment with HWC.This result suggested that cytoplasmic aggregation in culturedpotato cells might be connected with the association of actinfilaments. To identify the molecular basis of cytoplasmic aggregation,we purified actin and actin-related proteins by affinity chromatographyon a column of immobilized DNase I from cultured potato cellsand isolated proteins of 43 kDa, 32 kDa and 22 kDa. Analysisof the amino-terminal amino acid sequences indicated that the43 kDa, 32 kDa and 22 kDa proteins were potato actin, basicchitinase and osmotin-like protein, respectively. This conclusionwas supported by the results of Western blotting analysis ofthe 43 kDa and 32 kDa proteins with antibodies against actinand basic chitinase. Binding analysis with actin coupled toactin-specific antibodies and biotinylated actin suggested thatthe 32 kDa and 22 kDa proteins had actin-binding activity. Inaddition, examination of biomolecular interactions using anoptical biosensor confirmed the binding of chitinase to actin.These results imply the possibility that basic chitinase andosmotin-like protein might be involved in cytoplasmic aggregation,hereby participating in the potato cell's defense against attackby pathogen. (Received June 11, 1996; Accepted January 27, 1997)     

Nippostrongylus brasiliensis: Increase of sialomucins reacting with anti-mucin monoclonal antibody HCM31 in rat small intestinal mucosa with primary infection and reinfection

Infections with the parasitic helminth, Nippostrongylus brasiliensis, cause changes in rat small intestinal goblet cell mucin, particularly in the peripheral sugar residues of oligosaccharide. These changes may correlate with expulsion. In this study, we examined changes in mucin oligosaccharides caused by primary infection and reinfection with N. brasiliensis, using two monoclonal antibodies, HCM31 and PGM34, that react with sialomucin and sulfomucin, respectively. Enzyme-linked immunosorbent assay of jejunal mucins showed that the relative reactivity of mucins with HCM31, but not PGM34, increased up to 16 days after primary infection and 6 days after reinfection, the times when the worms were expelled from the rats. Immunohistochemical studies confirmed that goblet cells stained with HCM31 greatly increased at the time of worm expulsion. These results indicate that the marked increase observed in HCM31-reactive sialomucins may be related to expulsion of the worms.     

Alternative splicing variants of human arsenic (+3 oxidation state) methyltransferase

Arsenic (+3 oxidation state) methyltransferase (As3MT) catalyzes the methylation of trivalent arsenic (As(III)) to monomethylarsonate (MMA(V)) and dimethylarsinic acid (DMA(V)), and plays an important role in the detoxification of arsenicals. Here, we report the identification of two splicing variants of the human As3MT gene. One splicing variant was an exon-3 skipping (Δ3) form which produced a premature stop codon, and the other was an exon-4 and -5 skipping (Δ4,5) form which produced a 31.1 kDa As3MT protein. In addition to the full-length mRNA of As3MT, Δ4,5 mRNAs were detected in HepG2, A549, HL60, K562, and HEK293 cells. The methyltransferase activity of the recombinant Δ4,5 As3MT and wild-type As3MT proteins purified from Escherichia coli was determined. Speciation analysis by HPLC–ICP-MS showed a clear peak of MMA(V) after incubation of As(III) with the wild-type As3MT protein, but not with the Δ4,5 As3MT protein. In addition, COS-7 cells transfected with Δ4,5 As3MT cDNA did not convert As(III) to MMA(V) or DMA(V). The lack of methyltransferase activity of Δ4,5 As3MT seems to be related to the deletion of an S-adenosylmethionine-binding site and a critical cysteine residue. These data suggest that the expression pattern of splicing variants of the As3MT gene may affect the capacity for arsenic methylation in cells.     

Partial biopterin deficiency disturbs postnatal development of the dopaminergic system in the brain

Postnatal development of dopaminergic system is closely related to the development of psychomotor function. Tyrosine hydroxylase (TH) is the rate-limiting enzyme in the biosynthesis of dopamine and requires tetrahydrobiopterin (BH4) as a cofactor. To clarify the effect of partial BH4 deficiency on postnatal development of the dopaminergic system, we examined two lines of mutant mice lacking a BH4-biosynthesizing enzyme, including sepiapterin reductase knock-out (Spr(-/-)) mice and genetically rescued 6-pyruvoyltetrahydropterin synthase knock-out (DPS-Pts(-/-)) mice. We found that biopterin contents in the brains of these knock-out mice were moderately decreased from postnatal day 0 (P0) and remained constant up to P21. In contrast, the effects of BH4 deficiency on dopamine and TH protein levels were more manifested during the postnatal development. Both of dopamine and TH protein levels were greatly increased from P0 to P21 in wild-type mice but not in those mutant mice. Serotonin levels in those mutant mice were also severely suppressed after P7. Moreover, striatal TH immunoreactivity in Spr(-/-) mice showed a drop in the late developmental stage, when those mice exhibited hind-limb clasping behavior, a type of motor dysfunction. Our results demonstrate a critical role of biopterin in the augmentation of TH protein in the postnatal period. The developmental manifestation of psychomotor symptoms in BH4 deficiency might be attributable at least partially to high dependence of dopaminergic development on BH4 availability.     

Characterization of a protease that acts specifically on the 22-kDa protein in thylakoid membranes from green spores of the fern Osmunda japonica

A proteolytic enzyme responsible for the breakdown of a 22-kDa protein, whose abundance decreases in thylakoid membranes during germination of green spores of the fern Osmunda japonica , was partially purified from the thylakoid membranes of quiescent spores by a combination of ammonium sulfate fractionation, ion-exchange chromatography on DEAE-Toyopearl 650 S and size-fractionation HPLC on G3000SW. The enzyme was found to be a cysteine endoproteinase, as judged by its dependency on sulfhydryl reagents and inhibition by E-64 and iodoacetate, and by the appearance of distinct proteolytic products that were not further degraded during prolonged reaction time. Highest protease activity was observed around pH 9.7, the activity being partially suppressed by cations. The K_m of the 22-kDa protein as a substrate in the proteolysis was 67 μg ml⁻¹, equivalent to 3 μ M . The enzyme, with a native molecular mass of about 43 kDa, showed high specificity against the 22-kDa protein as a substrate. The isolated protease could not degrade the 22-kDa protein associated with fresh thylakoid membranes but digested the protein in the presence of 0.05% Triton X-100.     

Positive phototropism is accelerated in Biomphalaria glabrata snails by infection with Schistosoma mansoni

Parasite-induced behavioral changes in their hosts favor to complete the lifecycle of parasites. Schistosome infection is also known to cause physiological changes in infected freshwater snail intermediate hosts. Here, we report, a novel phenomenon in which Schistosoma mansoni, a highly debilitating worm affecting millions of people worldwide, alters the phototropic behavior of Biomphalaria glabrata, the vector snail. S. mansoni-infection enhanced positive phototropism of vector snails and infected snails spent significantly more time in light. Possibly, these behavioral changes help the parasite to be released efficiently from the infected intermediate hosts, and to infect mammalian hosts.     

Optimization of the hybridization-based method for purification of thermostable tRNAs in the presence of tetraalkylammonium salts

We found that both tetramethylammonium chloride (TMA-Cl) and tetra-ethylammonium chloride (TEA-Cl), which are used as monovalent cations for northern hybridization, drastically destabilized the tertiary structures of tRNAs and enhanced the formation of tRNA•oligoDNA hybrids. These effects are of great advantage for the hybridization-based method for purification of specific tRNAs from unfractionated tRNA mixtures through the use of an immobilized oligoDNA complementary to the target tRNA. Replacement of NaCl by TMA-Cl or TEA-Cl in the hybridization buffer greatly improved the recovery of a specific tRNA, even from unfractionated tRNAs derived from a thermophile. Since TEA-Cl destabilized tRNAs more strongly than TMA-Cl, it was necessary to lower the hybridization temperature at the sacrifice of the purity of the recovered tRNA when using TEA-Cl. Therefore, we propose two alternative protocols, depending on the desired properties of the tRNA to be purified. When the total recovery of the tRNA is important, hybridization should be carried out in the presence of TEA-Cl. However, if the purity of the recovered tRNA is important, TMA-Cl should be used for the hybridization. In principle, this procedure for tRNA purification should be applicable to any small-size RNA whose gene sequence is already known.     

A monoclonal antibody, PGM34, against 6-sulfated blood-group H type 2 antigen, on the carbohydrate moiety of mucin

Mucin, a major component of mucus, is a highly O-glycosylated, high-molecular-mass glycoprotein extensively involved in the physiology of gastrointestinal mucosa. To detect and characterize mucins derived from site-specific mucous cells, we developed a monoclonal antibody, designated PGM34, by immunizing a mouse with purified pig gastric mucin. The reactivity of PGM34 with mucin was inhibited by periodate treatment of the mucin, but not by trypsin digestion. This suggests that PGM34 recognizes the carbohydrate portion of mucin. To determine the epitope, oligosaccharide-alditols obtained from pig gastric mucin were fractionated by successive gel-filtration, ion-exchange, and normal-phase HPLC, and tested for reactivity with PGM34. Two purified oligosaccharide-alditols that reacted with PGM34 were obtained. Their structures were determined by NMR spectroscopy as Fucalpha1-2Galbeta1-4GlcNAc(6SO(3)H)beta1-6(Fucalpha1-2Galbeta1-3)GalNAc-ol and Fucalpha1-2Galbeta1-4GlcNAc(6SO(3)H)beta1-6(Galbeta1-3)GalNAc-ol. None of the defucosylated or desulfated forms of these oligosaccharides reacted with PGM34. Thus, the epitope of PGM34 was determined as the Fucalpha1-2Galbeta1-4GlcNAc(6SO(3)H)beta- sequence. Immunohistochemical examination of rat gastrointestinal tract showed that PGM34 stained surface mucous cells close to the generative cell zone in the gastric fundus and goblet cells in the small intestine, but only slightly stained antral mucous cells in the stomach. These data, taken together, show that PGM34 is a very useful tool for elucidating the role of mucins with characteristic sulfated oligosaccharides.