Supramolecular Polymer Polymorphism: Spontaneous Helix-Helicoid Transition through Dislocation of Hydrogen-Bonded π-Rosettes.

Polymorphism, a phenomenon whereby disparate self-assembled products can be formed from identical molecules, has incited interest in the field of supramolecular polymers. Conventionally, the monomers that constitute supramolecular polymers are engineered to facilitate one-dimensional aggregation and, consequently, their polymorphism surfaces primarily when the states of assembly differ significantly. This engenders polymorphs of divergent dimensionalities such as one- and two-dimensional aggregates. Notwithstanding, realizing supramolecular polymer polymorphism, wherein polymorphs maintain one-dimensional aggregation, persists as a daunting challenge. In this work, we expound upon the manifestation of two supramolecular polymer polymorphs formed from a large discotic supramolecular monomer (rosette), which consists of six hydrogen-bonded molecules with an extended π-conjugated core. These polymorphs are generated in mixtures of chloroform and methylcyclohexane, attributable to distinctly different disc stacking arrangements. The face-to-face (minimal displacement) and offset (large displacement) stacking arrangements can be predicated on their distinctive photophysical properties. The face-to-face stacking results in a twisted helix structure. Conversely, the offset stacking induces inherent curvature in the supramolecular fiber, thereby culminating in a hollow helical coil (helicoid). While both polymorphs exhibit bistability in nonpolar solvent compositions, the face-to-face stacking attains stability purely in a kinetic sense within a polar solvent composition and undergoes conversion into offset stacking through a dislocation of stacked rosettes. This occurs without the dissociation and nucleation of monomers, leading to unprecedented helicoidal folding of supramolecular polymers. Our findings augment our understanding of supramolecular polymer polymorphism, but they also highlight a distinctive method for achieving helicoidal folding in supramolecular polymers.

Toroid-rod supramolecular polymorphism derived from conformational isomerism of a π-conjugated system.

Hydrogen-bonded supermacrocycles (rosettes) composed of dinaphthylethene π-conjugated systems show unique supramolecular polymorphism affording nanorings and nanorods via kinetically controlled self-assembly. Molecular modeling and molecular dynamics simulations proposed that conformational isomerism of the π-conjugated systems leads to planar and convex rosette geometries, which results in their distinct stacking arrangements.

Asymmetric dimethylarginine, an endogenous NOS inhibitor, is actively metabolized in rat erythrocytes.

N(G), N(G)-Dimethyl-L-arginine (asymmetric dimethylarginine: ADMA) is an endogenous competitive inhibitor of nitric oxide synthase (NOS). Plasma ADMA concentrations have been reported to increase in connection with diseases associated with an impaired endothelial L-arginine/NO pathway. In this study, we investigated the metabolism of ADMA in circulating blood cell populations to elucidate the regulatory mechanism of elevation of plasma ADMA, a novel risk factor for cardiovascular disease. We found by RT-PCR and Western blot analyses that protein arginine methyltransferase (PRMT)1 and dimethylarginine dimethylaminohydrolase (DDAH)-1, responsible for the biosynthesis and degradation of ADMA respectively, are expressed in erythrocytes (ECs), leukocytes, and platelets. We also identified a major ADMA-containing protein in ECs as catalase, confirmed by GST-pull down assay to bind to PRMT1 in vitro. This is the first report that the ADMA-metabolizing system, including the arginine methylation of proteins and the breakdown of free ADMA, occurs in circulating blood cell-populations, and that catalase in ECs might be a potential protein targeted by PRMT1.

Hypoxia-inducible genes encoding small EF-hand proteins in rice and tomato.

Rice has evolved metabolic and morphological adaptations to low-oxygen stress to grow in submerged paddy fields. To characterize the molecular components that mediate the response to hypoxia in rice, we identified low-oxygen stress early response genes by microarray analysis. Among the highly responsive genes, five genes, OsHREF1 to OsHREF5, shared strong homology. They encoded small proteins harboring two EF-hands, typical Ca(2+)-binding motifs. Homologous genes were found in many land plants, including SlHREF in tomato, which is also strongly induced by hypoxia. SlHREF induction was detected in both roots and shoots of tomato plants under hypoxia. With the exception of OsHREF5, OsHREF expression was unaffected by drought, salinity, cold, or osmotic stress. Fluorescent signals of green fluorescent protein-fused OsHREFs were detected in the cytosol and nucleus. Ruthenium red, an inhibitor of intracellular Ca(2+) release, repressed induction of OsHREF1-4 under hypoxia. The HREFs may be related to the Ca(2+) response to hypoxia.

Influence of neighbouring base sequences on the mutagenesis induced by 7,8-dihydro-8-oxoguanine in yeast.

We have analysed the influence of neighbouring base sequences on the mutagenesis induced by 7,8-dihydro-8-oxoguanine (8-oxoG or G(o)), a typical oxidative lesion of DNA, using the yeast oligonucleotide transformation technique. Two oligonucleotides, oligo-CCG(o) and oligo-CGG(o), each possessing a single 8-oxoG residue and represented by the sequences 5'-CCG(o)-3' and 5'-CGG(o)-3', respectively, were introduced into a chromosome of Saccharomyces cerevisiae and their mutagenic potentials were compared. In a wild-type strain, 8-oxoG showed very weak mutagenic potential in both cases. However, the lesion in 5'-CCG(o)-3' can cause efficient G-to-T transversion in a strain lacking the rad30 gene which encodes yeast DNA polymerase eta (Ypoleta). To explore the properties associated with this translesion synthesis (TLS), the same two oligonucleotides possessing an 8-oxoG were used as templates for a standing-start primer extension assay, and the nucleotide incorporation opposite 8-oxoG was investigated. We found that dATP incorporation opposite 8-oxoG with Ypoleta was low for both sequences. In particular, very low dATP incorporation was observed for the 5'-CCG(o)-3' sequence. These results account for the efficient inhibition of mutagenesis by Ypoleta. TLS plays an important role in one DNA sequence in terms of avoiding mutagenesis induced by 8-oxoG in yeast. In contrast, human yeast DNA polymerase eta showed higher dATP incorporation rates even with the 5'-CCG(o)-3' sequence.

Template properties of mutagenic cytosine analogues in reverse transcription.

We have studied the mutagenic properties of ribonucleotide analogues by reverse transcription to understand their potential as antiretroviral agents by mutagenesis of the viral genome. The templating properties of nucleotide analogues including 6-(beta-D-ribofuranosyl)-3,4-dihydro-8H-pyrimido[4,5-c](1,2)oxazin-7-one, N4-hydroxycytidine, N4-methoxycytidine, N4-methylcytidine and 4-semicarbazidocytidine, which have been reported to exhibit ambiguous base pairing properties, were examined. We have synthesized RNA templates using T3 RNA polymerase, and investigated the specificity of the incorporation of deoxyribonucleoside triphosphates opposite these cytidine analogues in RNA by HIV and AMV reverse transcriptases. Except for N4-methylcytidine, both enzymes incorporated both dAMP and dGMP opposite these analogues in RNA. This indicates that they would be highly mutagenic if present in viral RNA. To study the basis of the differences among the analogues in the incorporation ratios of dAMP to dGMP, we have carried out kinetic analysis of incorporation opposite the analogues at a defined position in RNA templates. In addition, we examined whether the triphosphates of these analogues were incorporated competitively into RNA by human RNA polymerase II. Our present data supports the view that these cytidine analogues are mutagenic when incorporated into RNA, and that they may therefore be considered as candidates for antiviral agents by causing mutations to the retroviral genome.

Difference between deoxyribose- and tetrahydrofuran-type abasic sites in the in vivo mutagenic responses in yeast.

We have analyzed the mutagenic specificity of an abasic site in DNA using the yeast oligonucleotide transformation assay. Oligonucleotides containing an abasic site or its analog were introduced into B7528 or its derivatives, and nucleotide incorporation opposite abasic sites was analyzed. Cytosine was most frequently incorporated opposite a natural abasic site (O) ('C-rule'), followed by thymine. Deletion of REV1 decreased the transformation efficiency and the incorporation of cytosine nearly to a background level. In contrast, deletion of RAD30 did not affect them. We compared the mutagenic specificity with that of a tetrahydrofuran abasic site (F), an abasic analog used widely. Its mutation spectrum was clearly different from that of O. Adenine, not cytosine, was most favorably incorporated. However, deletion of REV1 decreased the transformation efficiency with F-containing oligonucleotide as in the case of O. These results suggest that the bypass mechanism of F is different from that of O, although the bypasses in both cases are dependent on REV1. We also found that the mutagenic specificity of F can be affected by not only the adjacent bases, but also a base located two positions away from F.

Roles of the polymerase and BRCT domains of Rev1 protein in translesion DNA synthesis in yeast in vivo.

Rev1p in yeast is essential for the translesion of abasic sites and 6-4 photoproducts. It plays a role as a translesion polymerase, but also supports translesion catalyzed by other polymerases. The protein has two domains, BRCT and Y-family polymerase. A point mutation in the BRCT domain is known to abolish the second function. In the present research, we have studied the effects of deletion of the BRCT domain and a point mutation at the two amino acids in the putative polymerase active center. We have introduced an abasic site, its tetrahydrofuran analog, and a 6-4 thymine-thymine photoproduct using the oligonucleotide transformation assay. Translesion efficiencies were estimated from the transforming activities of the oligonucleotides with a lesion, and the mutation spectra were analyzed by DNA sequencing of the transformants. Results showed that the lack of the BRCT domain reduced translesion efficiencies, but that substantial translesion synthesis took place. The mutation spectra of the lesions were not greatly affected. Therefore, the BRCT domain may be important, but dispensable for translesion synthesis. In contrast, the polymerase mutation, rev1AA, has only small effects on the translesion efficiencies, but the mutation spectra were greatly affected; the incorporation of dCMP opposite the lesions was specifically lost. This clearly shows that the polymerase domain is responsible for the dCMP incorporation. The effect of Poleta was also analyzed. From all the results DNA polymerases other than these two translesion polymerases, too, seem to initiate the translesion synthesis.

Use of yeast transformation by oligonucleotides to study DNA lesion bypass in vivo.

We have studied mutagenic specificities of DNA lesions in vivo in yeast CYC1 oligonucleotide transformation assay. We introduced two lesions into oligonucleotides. One was a nucleoside analog, 3,4-dihydro-6H,8H-pyrimido[4,5-c][1,2]oxazin-7-one 2'-deoxyriboside (dP), which is highly mutagenic to bacteria. It is supposed to be a miscoding, but otherwise good template for DNA polymerases. The other lesion was the TT pyrimidine(6-4)pyrimidone photoproduct, one of the typical UV lesions, which blocks DNA replication. These oligonucleotides were used to transform yeast cyc1 mutants with ochre nonsense mutation to Cyc1+. As expected from its templating properties in vitro, the transforming activity of dP-containing oligonucleotides was similar to those of unmodified oligonucleotides. Results indicated that dP may direct incorporation of guanine and adenine at a ratio of 1:20 or more in vivo. An oligonucleotide containing the photoproduct showed the transforming activity of as low as 3-5% of that of the corresponding unmodified oligonucleotide. This bypass absolutely required REV1 gene. The sequence analysis of the transformants has shown that the lesion was read as TT and TC at a ratio of 3:7, indicating its high mutagenic potential.

Oligonucleotide transformation for the study of mutagenic specificities of DNA lesions in yeast.

We developed a method for the analyzing mutagenic potential of DNA damage based on the oligonucleotide transformation technique in yeast. Using this assay we have analyzed mutagenic specificities of various DNA lesions. In the present study, we analyzed the mutagenic properties of 2-hydroxyadenine and 5-hydroxycytosine in yeast. Oligonucleotides containing 2-hydroxyadenine or 5-hydroxycytosine were used for the transformation. The oligonucleotides showed transforming activities similar to unmodified oligonucleotides. This indicates that no repair systems were working on them. The sequencing data of the transformants showed that 5-hydroxycytosine and 2-hydroxyadenine are read mainly as cytosine and adenine. We will also discuss the mechanism of oligonucleotide transformation and its application to the mutagenesis study.

Mutagenic properties of ribonucleotide analogues in reverse transcription with HIV and AMV reverse transcriptases.

Pyrimidine analogues, N4-hydroxycytosine (C(oh)), N4-methoxycytosine (C(mo)) and 6H, 8H-3,4-dihydropyrimido[4,5-c][1,2]oxazin-7-one (P) can form base pairs with both adenine and guanine. We examined the mutagenic properties of these ribonucleotide analogues in RNA in reverse transcription with HIV and AMV reverse transcriptases. Both reverse transcriptases incorporated dATP and dGTP opposite these analogues in RNA. The incorporation ratio of dGTP to dATP opposite each analogue was measured to estimate the potential for inducing U-to-C mutations. The potentials may be rC(oh) > rC(mo) > rP for both reverse transcriptases. It might be possible to induce mutations in the retroviral genomes and to develop a new antiviral therapy, if these analogues are incorporated by a human RNA polymerase.

Identification of essential amino acid residues of the NorM Na+/multidrug antiporter in Vibrio parahaemolyticus.

NorM is a member of the multidrug and toxic compound extrusion (MATE) family and functions as a Na+/multidrug antiporter in Vibrio parahaemolyticus, although the underlying mechanism of the Na+/multidrug antiport is unknown. Acidic amino acid residues Asp32, Glu251, and Asp367 in the transmembrane region of NorM are conserved in one of the clusters of the MATE family. In this study, we investigated the role(s) of acidic amino acid residues Asp32, Glu251, and Asp367 in the transmembrane region of NorM by site-directed mutagenesis. Wild-type NorM and mutant proteins with amino acid replacements D32E (D32 to E), D32N, D32K, E251D, E251Q, D367A, D367E, D367N, and D367K were expressed and localized in the inner membrane of Escherichia coli KAM32 cells, while the mutant proteins with D32A, E251A, and E251K were not. Compared to cells with wild-type NorM, cells with the mutant NorM protein exhibited reduced resistance to kanamycin, norfloxacin, and ethidium bromide, but the NorM D367E mutant was more resistant to ethidium bromide. The NorM mutant D32E, D32N, D32K, D367A, and D367K cells lost the ability to extrude ethidium ions, which was Na+ dependent, and the ability to move Na+, which was evoked by ethidium bromide. Both E251D and D367N mutants decreased Na+-dependent extrusion of ethidium ions, but ethidium bromide-evoked movement of Na+ was retained. In contrast, D367E caused increased transport of ethidium ions and Na+. These results suggest that Asp32, Glu251, and Asp367 are involved in the Na+-dependent drug transport process.

The role of deoxycytidyl transferase activity of yeast Rev1 protein in the bypass of abasic sites.

We have studied the mutagenic specificity of abasic sites using the yeast oligonucleotides transformation assay. We introduced oligonucleotide containing a natural abasic site and a tetrahydrofuran abasic site into Rev1 mutants, rev1AA, which contains mutations of Asp467 and Glu468 residues of Rev1p to Ala in order to inactivate dCMP transferase activity, and rev1 delta, which lacks its whole coding sequence. The transformation efficiencies of rev1AA with abasic-containing oligonucleotides were lower than those of B7528, a strain proficient in REV1 gene, but much higher than rev1 delta mutant. Sequence analysis opposite the lesions showed that the mutation spectra were different among these three strains.

Changes in surface roughness of erythrocytes due to shear stress: atomic force microscopic visualization of the surface microstructure.

Blood cells are subject to various kinds of stresses in flow fields. Hemolysis is the phenomenon in which a higher stress than normal damages the erythrocyte membrane and results in the leakage of its contents. Even if the stress is not strong enough to cause cell lysis, however, the cell membrane may sustain some damage. Therefore, to further improve the blood compatibility of artificial organs, the mechanisms of sublethal damage must be investigated. As a first step, we have analyzed the fine surface structure of sheared erythrocytes from a microscopic viewpoint by using an atomic force microscope (AFM) featuring nano meter-scale visualization. Sheep erythrocytes were sheared by a conventional cylindrical viscometer under sublethal shearing conditions. The duration of shear was set at 10 s, and the shearing rate was set at 0 (as control), 10000, and 50000/s. After being stressed, the cell surfaces were visualized by an AFM and the surface roughness was measured. As a result, the roughness value was found to increase with the shearing rate: 4.5 +/- 1.5 nm (0/s, control), 6.9 +/- 2.1 nm (10000/s, P < 0.01), and 10.1 +/- 2.4 nm (50000/s, P < 0.01).

UVA-induced degradation of 8-hydroxyguanine in oligonucleotide and the effect on its activities in yeast oligonucleotide transformation assay.

UVA-induced conversion of 8-hydroxyguanine in oligonucleotides was studied. By irradiation with 334 nm UVA light, 8-hydroxyguanine was completely changed to unknown compounds. Monomeric nucleoside may be much less labile to UVA. Mutagenic specificities of 8-hydroxyguanine were investigated using yeast oligonucleotide mutation assay. UVA irradiation moderately reduced the activity of the oligonucleotides.

Image analysis of remesothelialization following chemical wounding of cultured human peritoneal mesothelial cells: the role of hyaluronan synthesis.

BACKGROUND: To understand what happens during the wound healing process of the mesothelium, we have developed an in vitro wounding model of cultured human peritoneal mesothelial cells (HPMCs) utilizing an image acquisition and analysis system. Using this system, cell mobility and hyaluronan synthesis were quantified and their interrelationship discussed. METHODS: 1N NaOH was used to create circular wounds in cultured HPMC monolayers, which were then exposed for 30 minutes to the peritoneal dialysis solutions or fetal calf serum (FCS)-free M199 culture medium, followed by incubation with 0.3% FCS/M199 culture medium for up to 96 hours. Digitalized microscopic date was captured every 30 minutes to quantify the wound healing process. In separate experiments, the HPMC monolayers were stained with biotin-conjugated hyaluronan-binding protein (B-HABP) at a regular time interval. RESULTS: Centripetal migration of the HPMCs into the wound area was the predominant process involved in wound repair with proliferation playing a secondary role. Two noticeable observations were made from the digital video movies: (1) cell mobility varied and was dependent upon the morphology and location of the cell relative to the wound edge, and (2) cell migration continued even after wound closure. Staining for B-HABP was confined to the remesothelialized area when wound closure was complete at 24 hours. At 48 hours after wound closure, the stained area was even more visible, although somewhat diffuse; thereafter, staining was reduced to almost background levels. CONCLUSION: The cell culture model of wound healing used in our study has enabled us to demonstrate quantitative image data of the cellular processes that occur during wound healing. We have been able to continuously observe cell migration, proliferation, and transformation. Synthesis and subsequent decomposition of hyaluronan appears to be related to the mobility of the wounded and intact HPMCs in this model system.