Boronic Acid-Based Dendrimers with Various Surface Properties for Bacterial Recognition with Adjustable Selectivity

The need for a selective bacterial recognition method is evident to overcome the global problem of antibiotic resistance. Even though researchers have focused on boronic acid-based nanoprobes that immediately form boronate esters with saccharides at room temperature, the mechanism has not been well studied. We have developed boronic acid-modified poly(amidoamine) (PAMAM) dendrimers with various surface properties to investigate the mechanism of bacterial recognition. The boronic acid-based nanoprobes showed selectivity toward strains, species, or a certain group of bacteria by controlling their surface properties. Our nanoprobes showed selectivity toward Gram-positive bacteria or Escherichia coli K12W3110 without having to modify the boronic acid recognition sites. The results were obtained in 20 min and visible to the naked eye. Selectivity toward Gram-positive bacteria was realized through electrostatic interaction between the bacterial surface and the positively charged nanoprobes. In this case, the recognition target was lipoteichoic acid on the bacterial surface. On the other hand, pseudo-zwitterionic nanoprobes showed selectivity for E. coli K12W3110, indicating that phenylboronic acid did not recognize the outermost O-antigen on the lipopolysaccharide layer. Boronic acid-based nanoprobes with optimized surface properties are expected to be a powerful clinical tool to recognize multidrug-resistant strains or highly pathogenic bacteria.

Heterologous expression of flowering locus T promotes flowering but does not affect diurnal movement in the legume Lotus japonicus

Flowering locus T (FT) is known to promote flowering in response to photoperiodic conditions and has recently been shown to contribute to other phenomenon, such as diurnal stomatal movement. In legumes, FTs are classified into three subtypes, though the role of each subtype is not well defined. It has been reported that when FT of Lotus japonicus (LjFT) is heterologously expressed in Arabidopsis, LjFT functions as a mobile florigen to promote flowering, similar to Arabidopsis FT (AtFT). In this study, we expressed AtFT in L. japonicus using the SUC2 promoter and showed that heterologous expression of AtFT was able to promote flowering in the plant. We also showed that AtFT expression does not affect stomatal closing nor nyctinastic leaf movement. These findings contribute to our understanding of flower development and have potential application to breeding or plant biotechnology.

Rapid Bacterial Recognition over a Wide pH Range by Boronic Acid-Based Ditopic Dendrimer Probes for Gram-Positive Bacteria

We have developed a convenient and selective method for the detection of Gram-positive bacteria using a ditopic poly(amidoamine) (PAMAM) dendrimer probe. The dendrimer that was modified with dipicolylamine (dpa) and phenylboronic acid groups showed selectivity toward Staphylococcus aureus. The ditopic dendrimer system had higher sensitivity and better pH tolerance than the monotopic PAMAM dendrimer probe. We also investigated the mechanisms of various ditopic PAMAM dendrimer probes and found that the selectivity toward Gram-positive bacteria was dependent on a variety of interactions. Supramolecular interactions, such as electrostatic interaction and hydrophobic interaction, per se, did not contribute to the bacterial recognition ability, nor did they improve the selectivity of the ditopic dendrimer system. In contrast, the ditopic PAMAM dendrimer probe that had a phosphate-sensing dpa group and formed a chelate with metal ions showed improved selectivity toward S. aureus. The results suggested that the targeted ditopic PAMAM dendrimer probe showed selectivity toward Gram-positive bacteria. This study is expected to contribute to the elucidation of the interaction between synthetic molecules and bacterial surface. Moreover, our novel method showed potential for the rapid and species-specific recognition of various bacteria.

Gene Expression and Histochemical Analyses in the Fatty Livers of Rats Fed a Histidine-Excess Diet

Triglyceride (TG) and cholesterol accumulation are known to occur in the liver of rats fed a histidine-excess (5%) diet, but there are few studies reporting histochemical and molecular biological analyses of the rat liver. The aim of this study was to elucidate the molecular basis of this lipid-accumulation mechanism. Lipid accumulations, tissue section images, and gene expression levels were compared in the livers of rats fed a control or histidine-excess diet for 5 wk (n=8/group). Serum levels of TGs, free fatty acids, total cholesterol, high-density lipoprotein cholesterol, glucose, albumin, and the enzyme activities of aspartate aminotransferase and alanine aminotransferase were also analyzed. In the livers of rats fed a histidine-excess diet, histochemical analyses showed what appeared to be a preliminary stage of nonalcoholic fatty liver, characterized by lipid accumulation around the central vein area and minor fibrosis. However, there were no changes in serum TG or free fatty acid levels. Quantitative PCR analyses showed the up-regulation of FAT/CD36, which is related to the uptake of fatty acids into cells, and the downregulation of two apolipoprotein genes, ApoC3 and ApoE. The mRNA levels of PPARγ, LXRα, and AMPKα in the liver were also reduced by excess histidine intake. The results of this study suggest that steatosis caused by excess histidine intake may be the result of an imbalance between lipid transport from the liver and the uptake of free fatty acids into hepatocytes.

Rapid and Selective Discrimination of Gram-Positive and Gram-Negative Bacteria by Boronic Acid-Modified Poly(amidoamine) Dendrimer

There is an urgent need to develop a rapid and selective method for the detection of bacteria because delayed diagnosis and the overuse of antibiotics have triggered drug resistance in bacteria. To this end, we prepared boronic acid-modified poly(amidoamine) generation 4 (B-PAMAM(G4)) dendrimer as cross-linking molecules that form aggregates with bacteria. Within 5 min of adding B-PAMAM(G4) dendrimer solution to a bacterial suspension, large aggregates were observed. Interestingly, the aggregate formation with various bacteria was pH-dependent. In basic pH, both Gram-positive and Gram-negative bacteria formed aggregates, but in neutral pH, only Gram-positive bacteria formed aggregates. We revealed that this bacteria-selective aggregation involved the bacterial surface recognition of the phenylboronic acid moiety of B-PAMAM(G4) dendrimer. In addition, we demonstrated that the spherical structure of B-PAMAM(G4) was one of the important factors for the formation of large aggregates. The aggregation was also observed in the presence of ≤10 mM fructose. B-PAMAM(G4) dendrimer is expected to be a powerful tool for the rapid and selective discrimination between Gram-positive and Gram-negative bacteria.

Proline Decreases the Suppressive Effect of Histidine on Food Intake and Fat Accumulation

We recently suggested that proline might decrease the suppressive effect of histidine on food intake. Our purpose in the present study was to investigate the influence of proline on the suppressive effect of histidine on food intake and accumulation of body fat. Male Wistar rats were divided into four groups and allowed free access to the following diets for 3 wk: control (C), 5% proline (P), 5% histidine (H), or 5% histidine plus 10% proline (HP) diets. Food intake for 7 d and retroperitoneal fat tissue weight at the end of the experimental period of the HP diet group were greater than those of the H diet group, whereas no significant difference existed between the HP diet group and the C diet group. Our results indicate that proline inhibits the influence of histidine on food intake and accumulation of body fat.

Mutagenesis of apyrase conserved region 1 alters the nucleotide substrate specificity

Two apyrases having different substrate specificity, MP67 and MpAPY2, are present in Mimosa pudica. The substrate specificity of MP67 is quite high against ADP, and is distinct from any other apyrase. This might be attributed to the nucleotide binding motif (DXG) in apyrase conserved region 1. We performed a single amino acid substitution at position X in the motif. The ratio of the velocity of ATP/ADP hydrolysis was higher (approximately 1) for the S63A-MP67 mutant than for wild type-MP67 (0.19). Binding affinity for ADP of A75S-MpAPY2 mutant was increased to a level higher than that of the wild type MpAPY2. Thus, the residue at position X in the DXG motif plays an important role in determining nucleotide preference.

Isolation of heat-tolerant myoglobin from Asian swamp eel Monopterus albus

Myoglobin from Asian swamp eel Monopterus albus was purified from fish muscle using salt fractionation followed by column chromatography and molecular filtration. The purified Mb of 0.68 mg/g wet weight of muscle was determined for its molecular mass by MALDI-TOF-MS to be 15,525.18 Da. Using isoelectric focusing technique, the purified Mb showed two derivatives with pI of 6.40 and 7.12. Six peptide fragments of this protein identified by LC-MS/MS were homologous to Mbs of sea raven Hemitripterus americanus, yellowfin tuna Thunnus albacores, blue marlin Makaira nigicans, common carp Cyprinus carpio, and goldfish Carassius auratus. According to the Mb denaturation, the swamp eel Mb had thermal stability higher than walking catfish Clarias batrachus Mb and striped catfish Pangasius hypophthalmus Mb, between 30 and 60 (°)C. For the thermal stability of Mb, the swamp eel Mb showed a biphasic behavior due to the O(2) dissociation and the heme orientation disorder, with the lowest increase in both Kd(f) and Kd(s). The thermal sensitivity of swamp eel Mb was lower than those of the other Mbs for both of fast and slow reaction stages. These results suggest that the swamp eel Mb globin structure is thermally stable, which is consistent with heat-tolerant behavior of the swamp eel particularly in drought habitat.

Purification and biochemical characterization of a novel ecto-apyrase, MP67, from Mimosa pudica

We have previously reported the presence of an apyrase in Mimosa pudica. However, only limited information is available for this enzyme. Thus, in this study, the apyrase was purified to homogeneity. The purified enzyme had a molecular mass of around 67 kD and was able to hydrolyze both nucleotide triphosphate and nucleotide diphosphate as substrates. The ratio of ATP to ADP hydrolysis velocity of the purified protein was 0.01 in the presence of calcium ion, showing extremely high substrate specificity toward ADP. Thus, we designated this novel apyrase as MP67. A cDNA clone of MP67 was obtained using primers designed from the amino acid sequence of trypsin-digested fragments of the protein. In addition, rapid amplification of cDNA ends-polymerase chain reaction was performed to clone a conventional apyrase (MpAPY2). Comparison of the deduced amino acid sequences showed that MP67 is similar to ecto-apyrases; however, it was distinct from conventional apyrase based on phylogenetic classification. MP67 and MpAPY2 were expressed in Escherichia coli, and the recombinant proteins were purified. The recombinant MP67 showed high substrate specificity toward ADP rather than ATP. A polyclonal antibody raised against the recombinant MP67 was used to examine the tissue distribution and localization of native MP67 in the plant. The results showed that MP67 was ubiquitously distributed in various tissues, most abundantly in leaves, and was localized to plasma membranes. Thus, MP67 is a novel ecto-apyrase with extremely high substrate specificity for ADP.

Calcium-sensitive activity and conformation of Caenorhabditis elegans gelsolin-like protein 1 are altered by mutations in the first gelsolin-like domain

The gelsolin family of actin regulatory proteins is activated by Ca(2+) to sever and cap actin filaments. Gelsolin has six homologous gelsolin-like domains (G1-G6), and Ca(2+)-dependent conformational changes regulate its accessibility to actin. Caenorhabditis elegans gelsolin-like protein-1 (GSNL-1) has only four gelsolin-like domains (G1-G4) and still exhibits Ca(2+)-dependent actin filament-severing and -capping activities. We found that acidic residues (Asp-83 and Asp-84) in G1 of GSNL-1 are important for its Ca(2+) activation. These residues are conserved in GSNL-1 and gelsolin and previously implicated in actin-severing activity of the gelsolin family. We found that alanine mutations at Asp-83 and Asp-84 (D83A/D84A mutation) did not disrupt actin-severing or -capping activity. Instead, the mutants exhibited altered Ca(2+) sensitivity when compared with wild-type GSNL-1. The D83A/D84A mutation enhanced Ca(2+) sensitivity for actin severing and capping and its susceptibility to proteolytic digestion, suggesting a conformational change. Single mutations caused minimal changes in its activity, whereas Asp-83 and Asp-84 were required to stabilize Ca(2+)-free and Ca(2+)-bound conformations, respectively. On the other hand, the D83A/D84A mutation suppressed sensitivity of GSNL-1 to phosphatidylinositol 4,5-bisphosphate inhibition. The structure of an inactive form of gelsolin shows that the equivalent acidic residues are in close contact with G3, which may maintain an inactive conformation of the gelsolin family.

Topographical analyses of proliferation and differentiation of osteoblasts in micro- and macropores of apatite-fiber scaffold

A variety of calcium phosphates have been used for bone tissue-engineering applications. We developed porous hydroxyapatite (HAp) ceramics by firing green compacts consisting of spherical carbon beads and HAp fiber. The apatite-fiber scaffold (AFS) forms a three-dimensional network of fibers with two different pore sizes (micro- and macropores). In this study, we investigated cell distribution and fine cell structure in AFS by confocal laser scanning microscopy. Osteoblastic cells were permeated homogenously throughout the scaffold under static culture conditions and grew three-dimensionally in macropores of AFS. Cells penetrated into micropores when they were capable of cell-cell formations. Cell proliferation and differentiation were also evaluated by biochemical and molecular biological approaches. The expression levels of early-phase osteogenic genes in AFS increased immediately, and those of middle-phase genes were maintained during the 2-week study period. Furthermore, the expression of late-phase markers increased gradually during the incubation period. These data indicate that macropores provide sufficient space for cell growth and proliferation and that micropores facilitate cell differentiation via cell-cell networks. This study provides evidence for the effectiveness of three-dimensional culture systems comprising AFS, which mimics the microenvironment of bone cells.

Specific knockdown of delta-sarcoglycan gene in C2C12 in vitro causes post-translational loss of other sarcoglycans without mechanical stress

The precise role of delta-sarcoglycan (SG) that is constitutively expressed in skeletal muscle cells and may serve for maintaining the sarcolemmal integrity has not been identified. The delta-SG protein is at first among SG complex. To specifically identify the role in C(2)C(12) cells during the myogenesis, we screened several RNA interference (RNAi) candidates at first, and knocked down both levels of the mRNA and protein, employing adenovirus-mediated RNAi. We found no morphological alteration at both myoblast and myotube stages by suppression of delta-SG. The specific knockdown of delta-SG accompanied a concomitant decrease of alpha-, beta-, and gamma-SGs preserving normal levels of each transcript. As for the localization, alpha-, beta-, and gamma-SGs were weakly stained on the cell membrane in delta-SG knockdown cells, whereas each SG in control cell was localized both on the cell membrane and myoplasm abundantly. This enhanced post-translational loss would represent similitude of the progression of cardiomuscular diseases in vitro. Different from cardiac muscle cells, skeletal muscle cell culture without muscle contraction may imply that mechanical stress per se is not primarily involved in the progression of limb-girdle muscular dystrophy. Furthermore, we have observed translocation of calpain-2 to cell membrane in delta-SG knockdown cells, suggesting that Ca(2+)-sensitive proteases, calpains closely take part in post-translational proteolysis.

Specific knockdown of m-calpain blocks myogenesis with cDNA deduced from the corresponding RNAi

Fusion of mononuclear myoblast to multinucleated myotubes is crucial for myogenesis. Both mu- and m-calpain are ubiquitously expressed in most cells and are particularly abundant in muscle cells. Knockout of calpain-1 (catalytic subunit of mu-calpain) induced moderate platelet dysaggregation, preserving the normal development and growth, although knockout of calpain-2 (m-calpain) is lethal in mice. Therefore, there should be muscle-specific function of m-calpain per se. Previous methods lack direct evidence for the involvement of m-calpain, because the specific inhibitor to m-calpain has not been developed yet and the inhibition was less potent. Here, we show that screened RNA interference (RNAi) specifically blocked the m-calpain expression by 95% at both the protein and the activity levels. After transfection of adenovirus vector-mediated cDNA corresponding to the RNAi-induced short hairpin RNA, m-calpain in C(2)C(12) myoblasts was knocked down with no compensatory overexpression of mu-calpain or calpain-3. The specific knockdown strongly inhibited the fusion to multinucleated myotubes. In addition, the knockdown modestly blocked ubiquitous effects, including cell migration, cell spreading, and alignment of central stress fiberlike structures. These results may indicate that m-calpain requiring millimolar Ca(2+) level for the full activation plays specific roles in myogenesis, independent of mu-calpain, and leave us challenging problems in the future.

A novel hydroxyapatite fiber mesh as a carrier for recombinant human bone morphogenetic protein-2 enhances bone union in rat posterolateral fusion model

STUDY DESIGN

An experimental study, in which spinal fusion in rats was conducted using a hydroxyapatite fiber mesh (HAM) as a carrier for recombinant human bone morphogenetic protein (rhBMP)-2.

OBJECTIVES

To study the usefulness of the HAM as a carrier and seek the possibility of clinical application in spinal fusion.

SUMMARY OF BACKGROUND DATA

Several biomaterials have been used as a carrier for BMP to achieve spine fusion, however, to our knowledge, the most effective carrier has not been established.

METHODS

In experiment No. 1, HAMs and the controls (commercially available hydroxyapatite ceramic body), loaded with rhBMP-2, were immersed in phosphate-buffered saline to evaluate the time course of the release of rhBMP-2. In experiment No. 2, posterolateral fusion was conducted in rats using HAM and the control loaded with rhBMP-2. The fusion status was evaluated radiologically and histologically after surgery.

RESULTS

In experiment No. 1, HAMs released a larger amount of rhBMP-2 for up to 28 days than the controls (49.5% vs 7.8%). In experiment No. 2, the fusion rate was significantly higher in the HAM group (>80%) than in the control group (20%). Dense new bone formed close to the spine, and the HAMs were markedly absorbed compared with the controls.

CONCLUSION

HAM provided more solid fusion mass than the control, suggesting that HAM is an efficient carrier for BMP.

Change in the actin cytoskeleton during seismonastic movement of Mimosa pudica

The seismonastic movement of Mimosa pudica is triggered by a sudden loss of turgor pressure. In the present study, we compared the cell cytoskeleton by immunofluorescence analysis before and after movement, and the effects of actin- and microtubule-targeted drugs were examined by injecting them into the cut pulvinus. We found that fragmentation of actin filaments and microtubules occurs during bending, although the actin cytoskeleton, but not the microtubules, was involved in regulation of the movement. Transmission electron microscopy revealed that actin cables became loose after the bending. We injected phosphatase inhibitors into the severed pulvinus to examine the effects of such inhibitors on the actin cytoskeleton. We found that changes in actin isoforms, fragmentation of actin filaments and the bending movement were all inhibited after injection of a tyrosine phosphatase inhibitor. We thus propose that the phosphorylation status of actin at tyrosine residues affects the dynamic reorganization of actin filaments and causes seismonastic movement.

Partial sequence of connectin-like 1200K-protein in obliquely striated muscle of a polychaete (Annelida): evidence for structural diversity from vertebrate and invertebrate connectins

Vertebrate striated muscle contains the giant elastic protein connectin that maintains the position of the A-band at the center of the sarcomere during repeated muscular contraction and relaxation. Connectin-like molecules may perform conserved functions in vertebrate and invertebrate striated and oblique muscles, although less is known about the structure of invertebrate connectins at present. The protein that maintains such a structure is present not only in vertebrate striated muscle, but also in invertebrate striated and oblique muscle. In the present study, we analyzed the partial primary structure of a 1200K-protein, which is a connectin-like protein that is expressed in Neanthes sp. body wall muscle that is in turn composed of oblique muscle. Antibody screening of a cDNA library of Neanthes sp. body wall muscle identified two different clones. Both clones coded for a sequence predominantly comprised of the four amino acids proline (P), glutamate (E), valine (V) and lysine (K). One clone included a PEVK-like repeat sequence flanked by an Ig domain, while the other clone comprised a distinct 14 amino acid repeat rich in PEVK residues, flanked by a non-repetitive unique sequence. The PEVK region is found in vertebrate connectin and is thought to generate elasticity and be responsible for passive tension of the muscle. The antibodies produced against a portion of each clone both reacted with bands corresponding to 1200 kDa present in Neanthes sp. body wall muscle. Therefore, our results demonstrate that this 1200K-protein is a connectin-like elastic protein and includes specific PEVK-like fragment. We suggest that this 1200K-protein plays a major role in maintaining the structure of oblique muscle in invertebrates.

Expression and tissue distribution of astacin-like squid metalloprotease (ALSM)

Astacin metalloprotease family members function in a wide variety of biologic events, including cell differentiation and morphogenesis during embryonic development and adult tissue differentiation. We previously isolated and characterized an astacin-like squid metalloprotease (ALSM). To elucidate the embryonic expression of ALSM, we performed immunohistochemical analysis with specific antibodies and examined the expression profiles of ALSM isoforms by in situ hybridization analysis. Tissue distribution and expression were also examined in adult spear squid. mRNA expression of ALSM isoforms I and III was first detected in newly hatched squid and was restricted to the liver. No mRNA signals were detected in other tissues even in adult squids. At the protein level, both isoforms were prominent in the liver of embryos and later in digestive organs of adult squid. Both isoforms were also detected in muscle tissues, including mantle and tentacle muscle. Staining for ALSM III was also identified in the iris and in tissues near the eye in squid embryos. However, no reactive bands were detected by immunoblotting of adult squid eyes. Thus, ALSM is initially expressed at the late stage of embryogenesis in spear squid, and expression is restricted to the liver. Thereafter, ALSM isoforms function in various tissues in an isoform-dependent manner.

Water channel activities ofMimosa pudicaplasma membrane intrinsic proteins are regulated by direct interaction and phosphorylation

cDNAs encoding aquaporins PIP1;1, PIP2;1, and TIP1;1 were isolated from Mimosa pudica (Mp) cDNA library. MpPIP1;1 exhibited no water channel activity; however, it facilitated the water channel activity of MpPIP2;1 in a phosphorylation-dependent manner. Mutagenesis analysis revealed that Ser-131 of MpPIP1;1 was phosphorylated by PKA and that cooperative regulation of the water channel activity of MpPIP2;1 was regulated by phosphorylation of Ser-131 of MpPIP1;1. Immunoprecipitation analysis revealed that MpPIP1;1 binds directly to MpPIP2;1 in a phosphorylation-independent manner, suggesting that phosphorylation of Ser-131 of MpPIP1;1 is involved in regulation of the structure of the channel complex with MpMIP2;1 and thereby affects water channel activity.

Biochemical and immunohistochemical characterization of Mimosa annexin

To characterize the biochemical properties of plant annexin, we isolated annexin from Mimosa pudica L. and analyzed the biochemical properties conserved between Mimosa annexin and animal annexins, e.g. the ability to bind phospholipid and F-actin in the presence of calcium. We show that Mimosa annexin is distributed in a wide variety of tissues. Immunoblot analysis also revealed that the amount of annexin is developmentally regulated. To identify novel functions of Mimosa annexin, we examined the pattern of distribution and the regulation of its expression in the pulvinus. The amount of annexin in the pulvinus increased at night and was sensitive to abscisic acid; however, there was no detectable induction of annexin by cold or mechanical stimulus. Annexin distribution in the cell periphery during the daytime was changed to a cytoplasmic distribution at night, indicating that Mimosa annexin may contribute to the nyctinastic movement in the pulvinus.

Biochemical and molecular biological analysis of different responses to 2,3,7,8-tetrachlorodibenzo-p-dioxin in chick embryo heart and liver

We studied the mechanism of toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in the chick embryo, which is an organism highly sensitive to TCDD. TCDD was injected into egg yolks prior to embryogenesis, and eggs were incubated for 12 or 18 days. In TCDD-exposed embryos, we observed increased heart wet weight and change in the color of the liver, with abnormal fatty vesicle formation. To determine whether these effects were mediated by the aryl hydrocarbon receptor (AhR), we examined expression levels of AhR, CYP1A4, and CYP1A5. AhR was expressed continuously in the heart and liver during embryogenesis, whereas induction of CYP1A4 and CYP1A5 by TCDD was detected only in the liver. In situ hybridization study of tissue sections revealed induction of CYP1A4 in the abnormal liver tissue in which color change was not observed. To determine whether these different responses to TCDD depended on the cell type, primary cultures of chick hepatocytes and cardiac myocytes were established and 7-ethoxyresorufin-O-deethylase (EROD) activity was measured. Induction of EROD activity following exposure to TCDD was detected in hepatocytes but not in cardiac myocytes. Although the heart is a principal target organ for TCDD toxicity and AhR is expressed throughout embryogenesis, induction of CYP1A was not observed in the chick heart. Thus, we conclude that defects in the heart induced by exposure to TCDD occur via a different pathway than that occurring in the liver.

Induction and patterning of the Purkinje fibre network

Impulse-conducting Purkinje cells differentiate from myocytes during embryogenesis. In the embryonic chicken heart, this conversion of contractile myocytes into conduction cells occurs subendocardially and periarterially. The unique sites of Purkinje fibre differentiation suggest that a shear stress-induced paracrine signal from the endocardium and arterial beds may induce adjacent myocytes to differentiate into conduction cells. Consistent with this model, Purkinje fibre marker genes can be induced in cultured embryonic myocytes by endothelin (ET), an endothelial cell-derived signalling peptide. This inductive response is, however, gradually lost from myocytes as embryos develop, and mature myocytes express only genes characteristic of hypertrophy in response to ET. In vivo, active ET is produced, through proteolytic processing, from its precursor by ET-converting enzyme 1 (ECE1) and triggers signalling by binding to its receptors, ETA and ETB. In the embryonic heart, the expression of these ET signalling components changes dynamically, defining the site and timing of Purkinje fibre differentiation within the ventricular myocardium during chick embryogenesis.

Achacin induces cell death in HeLa cells through two different mechanisms

Achacin, which belongs to the L-amino acid oxidase group, oxidizes free amino acids and produces hydrogen peroxide in cell culture systems. Morphological changes in cells incubated with achacin were similar to those of cells incubated with H(2)O(2). In both cases, the end result was cell death. To examine the mechanism of achacin-associated cytotoxicity, the H(2)O(2) scavenger catalase was added to culture media. Features typical of apoptosis, including morphological changes, DNA fragmentation, and PARP cleavage, were observed when cells were incubated with achacin in the presence of catalase. Moreover, apoptosis was inhibited by Z-VAD-fmk, a broad-spectrum caspase inhibitor. Herein, we present evidence that two pathways are involved in achacin-induced cell death. One is direct generation of H(2)O(2) through the L-amino acid oxidase activity of achacin. The other is the caspase-mediated apoptotic pathway that is induced by depletion of L-amino acids by achacin.

Solubility Properties of a 65-kDa Peptide Prepared by Restricted Digestion of Myosin with Astacin-like Squid Metalloprotease

Substructure of the myosin rod and its correlation to filament formation is largely based on studies of proteolytic digests and expressed proteins. However, tryptic digestion of myosin always produces polymorphous peptides. Consequently, it is difficult to determine the relation between myosin substructure and filament formation. Similarly, filament formation with recombinant myosin protein is also difficult to interpret because it is never clear whether the recombinant protein folds like the native protein. We recently reported a novel metal protease isolated from squid liver, astacin-like squid metalloprotease (ALSM), which can specifically hydrolyze in vitro myosin heavy chain. In the present study, we examined the solubility properties of the 65-kDa peptide and light meromyosin (LMM) prepared by ALSM isoform II and trypsin digestion, respectively. The 65-kDa peptide is much less soluble than LMM under physiological conditions, even though the length of 65-kDa peptide is shorter than that of LMM. These results suggest that a novel substructure of myosin drives filament assembly.

Antimicrobial action of achacin is mediated by L-amino acid oxidase activity

Achacin is an antibacterial glycoprotein purified from the mucus of the giant snail, Achatina fulica Férussac, as a humoral defense factor. We showed that achacin has L-amino acid oxidase activity and can generate cytotoxic H(2)O(2); however, the concentration of H(2)O(2) was not sufficient to kill bacteria. The antibacterial activity of achacin was inhibited by various H(2)O(2) scavengers. Immunochemical analysis revealed that achacin was preferentially bound to growth-phase bacteria, accounting for the important role in growth-phase-dependent antibacterial activity of achacin. Achacin may act as an important defense molecule against invading bacteria.

Cloning and biochemical characterization of astacin-like squid metalloprotease

We have cloned four cDNAs encoding astacin-like squid metalloproteases (ALSMs)-I and -II from the Japanese common squid and ALSMs-I and -III from the spear squid. Analysis of the deduced amino acid sequences revealed that ALSMs possess a signal peptide and a pro-sequence followed by an astacin-like catalytic domain and an MAM (meprin, A5 protein, receptor protein-tyrosine phosphatase mu) domain. Phylogenetic analysis revealed that ALSM corresponds to a new cluster of astacins. To analyze the function of the MAM domain, wild-type ALSM and an MAM-truncated mutant were expressed in a baculovirus expression system. The expressed protein encoding full-length ALSM hydrolyzed myosin heavy chain as effectively as native ALSM, whereas the MAM-truncated mutant possessed no protease activity, suggesting that the MAM domain contributes to substrate recognition. ALSM has been isolated from squid liver and mantle muscle. However, analysis with a specific antibody generated against ALSM indicated the presence of ALSM in a wide variety of tissues. ALSM was located in the extracellular matrix of mantle muscle cells. Thus, ALSM is a secreted protease, as are other members of the astacin family. The extracellular localization raises the possibility of substrates other than myosin. The physiological role of ALSM remains unknown, at this time.

Competency of embryonic cardiomyocytes to undergo Purkinje fiber differentiation is regulated by endothelin receptor expression

Purkinje fibers of the cardiac conduction system differentiate from heart muscle cells during embryogenesis. In the avian heart, Purkinje fiber differentiation takes place along the endocardium and coronary arteries. To date, only the vascular cytokine endothelin (ET) has been demonstrated to induce embryonic cardiomyocytes to differentiate into Purkinje fibers. This ET-induced Purkinje fiber differentiation is mediated by binding of ET to its transmembrane receptors that are expressed by myocytes. Expression of ET converting enzyme 1, which produces a biologically active ET ligand, begins in cardiac endothelia, both arterial and endocardial, at initiation of conduction cell differentiation and continues throughout heart development. Yet, the ability of cardiomyocytes to convert their phenotype in response to ET declines as embryos mature. Therefore, the loss of responsiveness to the inductive signal appears not to be associated with the level of ET ligand in the heart. This study examines the role of ET receptors in this age-dependent loss of inductive responsiveness and the expression profiles of three different types of ET receptors, ETA, ETB and ETB2, in the embryonic chick heart. Whole-mount in situ hybridization analyses revealed that ETA was ubiquitously expressed in both ventricular and atrial myocardium during heart development, while ETB was predominantly expressed in the atrium and the left ventricle. ETB2 expression was detected in valve leaflets but not in the myocardium. RNase protection assays showed that ventricular expression of ETA and ETB increased until Purkinje fiber differentiation began. Importantly, the levels of both receptor isotypes decreased after this time. Retrovirus-mediated overexpression of ETA in ventricular myocytes in which endogenous ET receptors had been downregulated, enhanced their responsiveness to ET, allowing them to differentiate into conduction cells. These results suggest that the developmentally regulated expression of ET receptors plays a crucial role in determining the competency of ventricular myocytes to respond to inductive ET signaling in the chick embryo.

Invertebrate connectin spans as much as 3.5 microm in the giant sarcomeres of crayfish claw muscle

In crayfish claw closer muscle, the giant sarcomeres are 8.3 microm long at rest, four times longer than vertebrate striated muscle sarcomeres, and they are extensible up to 13 microm upon stretch. Invertebrate connectin (I-connectin) is an elastic protein which holds the A band at the center of the sarcomere. The entire sequence of crayfish I-connectin was predicted from cDNA sequences of 53 424 bp (17 352 residues; 1960 kDa). Crayfish I-connectin contains two novel 68- and 71-residue repeats, and also two PEVK domains and one kettin region. Kettin is a small isoform of I-connectin. Immunoblot tests using antibody to the 68-residue repeats revealed the presence of I-connectin also in long sarcomeres of insect leg muscle and barnacle ventral muscle. Immunofluorescence microscopy demonstrated that the two repeats, the long spacer and the two PEVK domains contribute to sarcomere extension. These regions rich in charged amino acids, occupying 63% of the crayfish I-connectin molecule, may allow a span of a 3.5 microm distance as a new class of composite spring.

The gelsolin/fragmin family protein identified in the higher plant Mimosa pudica

Mimosa pudica L. rapidly closes its leaves and bends its petioles downward when mechanically stimulated. It has been suggested that the actin cytoskeleton is involved in the bending motion since both cytochalasin B and phalloidin inhibit the motion. In order to clarify the mechanism by which the actin cytoskeleton functions in the motion, we attempted to find actin-modulating proteins in the M. pudica plant by DNase I-affinity column chromatography. The EGTA-eluate from the DNase I column contained proteins with apparent molecular masses of 90- and 42-kDa. The 42-kDa band consisted of two closely migrating components: the slower migrating component was actin while the faster migrating components was a distinct protein. The eluate showed an activity to sever actin filaments and to enhance the rate of polymerization of actin, both in a Ca(2+)-dependent manner. Microsequencing of the faster migrating 42-kDa protein revealed its similarity to proteins in the gelsolin/fragmin family. Our results provide the first biochemical evidence for the presence in a higher plant of a gelsolin/fragmin family actin-modulating protein that severs actin filament in a Ca(2+)-dependent manner.

Psychrophilic valine dehydrogenase of the antarctic psychrophile, Cytophaga sp. KUC-1: purification, molecular characterization and expression

We found the occurrence of valine dehydrogenase in the cell extract of a psychrophilic bacterium, Cytophaga sp. KUC-1, isolated from Antarctic seawater and purified the enzyme to homogeneity. The molecular mass of the enzyme was determined to be approximately 154 kDa by gel filtration and that of the subunit was 43 kDa by SDS/PAGE: the enzyme was a homotetramer. The enzyme required NAD+ as a coenzyme, and catalyzed the oxidative deamination of L-valine, L-isoleucine, L-leucine and the reductive amination of alpha-ketoisovalerate, alpha-ketovalerate, alpha-ketoisocaproate, and alpha-ketocaproate. The reaction proceeds through an iso-ordered bi-bi mechanism. The enzyme was highly susceptible to heat treatment and the half-life at 45 degrees C was estimated to be 2.4 min. The kcat/Km (micro(-1).s(-1)) values for L-valine and NAD+ at 20 degrees C were 27.48 and 421.6, respectively. The enzyme showed pro-S stereospecificity for hydrogen transfer at the C4 position of the nicotinamide moiety of coenzyme. The gene encoding valine dehydrogenase was cloned into Escherichia coli (Novablue), and the primary structure of the enzyme was deduced on the basis of the nucleotide sequence of the gene encoding the enzyme. The enzyme contains 370 amino-acid residues, and is highly homologous with S. coelicolor ValDH (identity, 46.7%) and S. fradiae ValDH (43.1%). Cytophaga sp. KUC-1 ValDH contains much lower numbers of proline and arginine residues than those of other ValDHs. The changes probably lead to an increase in conformational flexibility of the Cytophaga enzyme molecule to enhance the catalytic activity at low temperatures.

In vivo induction of cardiac Purkinje fiber differentiation by coexpression of preproendothelin-1 and endothelin converting enzyme-1

The rhythmic heart beat is coordinated by electrical impulses transmitted from Purkinje fibers of the cardiac conduction system. During embryogenesis, the impulse-conducting cells differentiate from cardiac myocytes in direct association with the developing endocardium and coronary arteries, but not with the venous system. This conversion of myocytes into Purkinje fibers requires a paracrine interaction with blood vessels in vivo, and can be induced in vitro by exposing embryonic myocytes to endothelin-1 (ET-1), an endothelial cell-associated paracrine factor. These results suggest that an endothelial cell-derived signal is capable of inducing juxtaposed myocytes to differentiate into Purkinje fibers. It remains unexplained how Purkinje fiber recruitment is restricted to subendocardial and periarterial sites but not those juxtaposed to veins. Here we show that while the ET-receptor is expressed throughout the embryonic myocardium, introduction of the ET-1 precursor (preproET-1) in the embryonic myocardium is not sufficient to induce myocytes to differentiate into conducting cells. ET converting enzyme-1 (ECE-1), however, is expressed preferentially in endothelial cells of the endocardium and coronary arteries where Purkinje fiber recruitment takes place. Retroviral-mediated coexpression of both preproET-1 and ECE-1 in the embryonic myocardium induces myocytes to express Purkinje fiber markers ectopically and precociously. These results suggest that expression of ECE-1 plays a key role in defining an active site of ET signaling in the heart, thereby determining the timing and location of Purkinje fiber differentiation within the embryonic myocardium.

Purification and characterization of a novel isoform of myosinase from spear squid liver

A novel isoform of myosinase was purified to homogeneity from liver of spear squid by sequential chromatographies using SP Sephadex, hydroxylapatite, Zn/Co chelating affinity, and TSK-gel G2000SW columns. Myosinase activity was detected as a single peak of 45-kDa protein by gel filtration. The novel isoform of myosinase specifically hydrolyzed a rabbit skeletal muscle myosin heavy chain into products of 120 and 100 kDa in the presence of Co(2+) ions, and the cleavage site in the myosin heavy chain was quite different from those of two known myosinase isoforms, I and II. Therefore, we named the novel isoform myosinase III. Myosinase III was also distinguishable from myosinase I by its amino-terminal sequence. The sequence showed similarity to an internal sequence of the astacin family.

A partial connectin cDNA encoding a novel type of RSP motifs isolated from chicken embryonic skeletal muscle

A partial cDNA encoding 811 amino acids of connectin (titin), a giant elastic protein of muscle (3,000 kDa), was cloned from a chicken embryonic skeletal muscle cDNA library using antibodies to muscle connectin. The encoded product was the C terminal segment of connectin. The predicted sequences consisted of 5 type II motifs (immunoglobulin C2 type) separated by 5 interdomain insertions. One interdomain insertion had significant homology (RSP) to KSP repeats found in human cardiac C-terminal connectin and another had a high sequence homology to porin (67.7%; 31 amino acids).

A novel domain sequence of connectin localized at the I band of skeletal muscle sarcomeres: homology to neurofilament subunits

A cDNA of 4.0 kb was cloned from a chicken embryo skeletal muscle cDNA library, using an antibody to muscle elastic protein connectin (titin), the molecular mass of which is estimated to be 3,000 kDa. Immunoelectron microscopy revealed that the antiserum raised against the product of the cDNA expressed in E. coli bound to the epitopes of the connectin filament near the N2 line of chicken breast muscle sarcomeres. The predicted amino acid sequence contains eight immunoglobulin C2 motifs and regions highly homologous with the high and medium molecular weight subunits of neurofilament. In addition, there are regions homologous with desmoplakin, calsequestrin, and calpastatin.