Minor but key chlorophylls in Photosystem II

A ‘metal-free’ chlorophyll (Chl) a, pheophytin (Phe) a, functions as the primary electron acceptor in PS II. On the basis of Phe a/PS II = 2, Phe a content is postulated as an index for estimation of the stoichiometry of pigments and photosystems. We found Phe a in a Chl d-dominant cyanobacterium Acaryochloris marina, whereas Phe d was absent. The minimum Chl a:Phe a ratio was 2:2, indicating that the primary electron donor is Chl a, accessory is Chl d, and the primary electron acceptor is Phe a in PS II of A. marina. Chl d was artificially formed by the treatment of Chl a with papain in aqueous organic solvents. Further, we will raise a key question on the mechanisms of water oxidation in PS II.     

Identification of a 3.0-kb major recombination hotspot in patients with Sotos syndrome who carry a common 1.9-Mb microdeletion

Sotos syndrome (SoS) is a congenital dysmorphic disorder characterized by overgrowth in childhood, distinctive craniofacial features, and mental retardation. Haploinsufficiency of the NSD1 gene owing to either intragenic mutations or microdeletions is known to be the major cause of SoS. The common approximately 2.2-Mb microdeletion encompasses the whole NSD1 gene and neighboring genes and is flanked by low-copy repeats (LCRs). Here, we report the identification of a 3.0-kb major recombination hotspot within these LCRs, in which we mapped deletion breakpoints in 78.7% (37/47) of patients with SoS who carry the common microdeletion. The deletion size was subsequently refined to 1.9 Mb. Sequencing of breakpoint fragments from all 37 patients revealed junctions between a segment of the proximal LCR (PLCR-B) and the corresponding region of the distal LCR (DLCR-2B). PLCR-B and DLCR-2B are the only directly oriented regions, whereas the remaining regions of the PLCR and DLCR are in inverted orientation. The PLCR, with a size of 394.0 kb, and the DLCR, with a size of of 429.8 kb, showed high overall homology (approximately 98.5%), with an increased sequence similarity (approximately 99.4%) within the 3.0-kb breakpoint cluster. Several recombination-associated motifs were identified in the hotspot and/or its vicinity. Interestingly, a 10-fold average increase of a translin motif, as compared with the normal distribution within the LCRs, was recognized. Furthermore, a heterozygous inversion of the interval between the LCRs was detected in all fathers of the children carrying a deletion in the paternally derived chromosome. The functional significance of these findings remains to be elucidated. Segmental duplications of the primate genome play a major role in chromosomal evolution. Evolutionary study showed that the duplication of the SoS LCRs occurred 23.3-47.6 million years ago, before the divergence of Old World monkeys.     

Characterization of the interaction between interleukin-13 and interleukin-13 receptors

Interleukin-13 (IL-13) possesses two types of receptor: the heterodimer, composed of the IL-13Ralpha1 chain (IL-13Ralpha1) and the IL-4Ralpha chain (IL-4Ralpha), transducing the IL-13 signals; and the IL-13Ralpha2 chain (IL-13Ralpha2), acting as a nonsignaling "decoy" receptor. Extracellular portions of both IL-13Ralpha1 and IL-13Ralpha2 are composed of three fibronectin type III domains, D1, D2, and D3, of which the last two comprise the cytokine receptor homology modules (CRHs), a common structure of the class I cytokine receptor superfamily. Thus far, there has been no information about the critical amino acids of the CRHs or the role of the D1 domains of IL-13Ralpha1 and IL-13Ralpha2 in binding to IL-13. In this study, we first built the homology modeling of the IL-13.hIL-13 receptor complexes and then predicted the amino acids involved in binding to IL-13. By incorporating mutations into these amino acids, we identified Tyr-207, Asp-271, Tyr-315, and Asp-318 in the CRH of human IL-13Ralpha2, and Leu-319 and Tyr-321 in the CRH of human IL-13Ralpha1, as critical residues for binding to IL-13. Tyr-315 in IL-13Ralpha2 and Leu-319 in IL-13Ralpha1 are positionally conserved hydrophobic amino acid residues. Furthermore, by using D1 domain-deleted mutants, we found that the D1 domain is needed for the expression of IL-13Ralpha2, but not IL-13Ralpha1, and that the D1 domain of IL-13Ralpha1 is important for binding to IL-13, but not to IL-4. These results provide the basis for a precise understanding of the interaction between IL-13 and its receptors.     

The receptor and transporter for internalization of Clostridium botulinum type C progenitor toxin into HT-29 cells

Orally ingested botulinum toxin enters the circulatory system and eventually reaches the peripheral nerves, where it elicits a response of neurological dysfunction. In this study, we report the important findings concerning the mechanism of Clostridium botulinum type C progenitor toxin (C16S) endocytic mechanism. C16S toxin bound to high molecular weight proteins on the surface of human colon carcinoma HT-29 cells and was internalized, but not if the cells were pretreated with neuraminidase. Benzyl-GalNAc which inhibited O-glycosylation of glycoproteins also interfered in the toxin's ability to bind the cell surface. On the other hand, the toxin was internalized in spite of pretreatment of the cells with PPMP, an inhibitor of ganglioside synthesis. These results suggest that the glycoproteins, like mucin, fulfill the important roles of receptor and transporter of C16S toxin.     

Treatment with alpha-galactosylceramide attenuates the development of bleomycin-induced pulmonary fibrosis

Pulmonary fibrosis is an end-stage disorder for which efficacious therapeutic options are not readily available. Although its pathogenesis is poorly understood, pulmonary fibrosis occurs as a result of various inflammations. NKT cells modulate inflammation because of their ability to produce large amounts of cytokines by stimulation with their glycolipid ligand. In the present study, we investigated the effects of alpha-galactosylceramide (alpha-GalCer), a selective NKT cell ligand, on the development of bleomycin-induced pulmonary fibrosis. Treatment of mice with alpha-GalCer prolonged their survival under bleomycin administration by attenuating the development of pulmonary fibrosis. The protective effects of alpha-GalCer were associated with an increase in the pulmonary level of IFN-gamma and a decrease in the pulmonary level of fibrogenic cytokines such as TGF-beta and connective tissue growth factor. The initial pulmonary inflammation caused by bleomycin was also attenuated by alpha-GalCer with the reduction of the macrophage inflammatory protein-2 level. The protective effects of alpha-GalCer were markedly reduced in mice lacking NKT cells or as a result of treatment with anti-IFN-gamma Ab. These results suggest that alpha-GalCer suppresses bleomycin-induced acute pulmonary inflammation and thus attenuates the development of pulmonary fibrosis possibly by regulating several cytokine levels.     

ADP-binding to origin recognition complex of Saccharomyces cerevisiae

The origin recognition complex (ORC), a possible initiator of chromosomal DNA replication in eukaryotes, binds to ATP through its subunits Orc1p and Orc5p. Orc1p possesses ATPase activity. As for DnaA, the Escherichia coli initiator, the ATP-DnaA complex is active but the ADP-DnaA complex is inactive for DNA replication and, therefore, the ATPase activity of DnaA inactivates the ATP-DnaA complex to suppress the re-initiation of chromosomal DNA replication. We investigated ADP-binding to ORC by a filter-binding assay. The K(d) values for ADP-binding to wild-type ORC and to ORC-1A (ORC containing Orc1p with a defective Walker A motif) were less than 10nM, showing that Orc5p can bind to ADP with a high affinity, similar to ATP. ORC-5A (ORC containing Orc5p with a defective Walker A motif) did not bind to ADP, suggesting that the ADP-Orc1p complex is too unstable to be detected by the filter-binding assay. ADP dissociated more rapidly than ATP from wild-type ORC and ORC-1A. Origin DNA fragments did not stimulate ADP-binding to any type of ORC. In the presence of ADP, ORC could not bind to origin DNA in a sequence-specific manner. Thus, in eukaryotes, the ADP-ORC complex may be unable to initiate chromosomal DNA replication, and in this it resembles the ADP-DnaA complex in prokaryotes. However, overall control may be different. In eukaryotes, the ADP-ORC complex is unstable, suggesting that the ADP-ORC complex might rapidly become an ATP-ORC complex; whereas in prokaryotes, ADP remains bound to DnaA, keeping DnaA inactive, and preventing re-initiation for some periods.     

Expression of vascular endothelial growth factor (VEGF) and its cognate receptors in human pheochromocytomas

Pheochromocytomas are well-vascularized tumors, suggesting that a potent angiogenic factor may be involved in the mechanism of their formation. As vascular endothelial growth factor (VEGF) is a potent mitogen for vascular endothelial cells, here we have investigated the mRNA and protein expression of VEGF and the mRNA expression of its two receptors (Flt-1 and Flk-1/KDR) in pheochromocytomas tissue. An increase in VEGF mRNA (mainly isoforms VEGF(121) and VEGF(165)) and in VEGF protein expression were observed by semi-quantitative RT-PCR and Western blot, respectively, compared to normal adrenomedullary tissue. Flk-1/KDR, and Flt-1 levels of mRNA were also increased markedly in tumors and correlated with levels of VEGF mRNA. Therefore, we speculate that upregulation of VEGF expression and its receptors might be important in the pathogenesis of pheochromocytomas.     

Production of prostaglandinE2 via bile acid is enhanced by trypsin and acid in normal human esophageal epithelial cells

Several reports suggest that duodenogastroesophageal reflux may produce esophagitis, Barrett's esophagus and esophageal carcinoma. And it is well known that the incidence of adenocarcinoma arising from Barrett's esophagus has been increasing during the past decade. On the other hand, cyclooxygenase-2 and prostaglandins, produced by the catalytic reaction of cyclooxygenase-2, are considered to relate to carcinogenesis of the digestive tract and other malignant tumors. Recent reports suggest that cyclooxygenase-2 is induced in Barrett's esophagus and esophageal carcinoma. The purpose of this study is to investigate the reaction of cyclooxygenase-2 expression and prostaglandinE2 production on normal human esophageal epithelial cells cultured with gastroduodenal components. Normal human esophageal epithelial cells were cultured with chenodeoxycholic acid, trypsin and in acidic condition, individually and with different combinations of these three factors. After culturing, cyclooxygenase-2 expression in the cells and amount of prostglandinE2 in culture media was evaluated by immunoblotting and enzyme-immunoassay, respectively after culturing the cells. Cyclooxygenase-2 expression was up-regulated by bile acid and prostaglandinE2 production was enhanced by bile acid with trypsin, acidic condition or both of these components, without a synergistic effect on cyclooxygenase-2 expression. Production of prostaglandinE2 via these factors was suppressed by the cyclooxygenase-2 selective inhibitor JTE-522.The results suggest that duodenogastroesophageal reflux may induce cyclooxygenase-2 expression and prostaglandinE2 production in esophageal epithelial cells, cyclooxygenase-2 specific inhibitors may have a chemopreventive effect on esophageal carcinoma.     

Orally administered rosmarinic acid is present as the conjugated and/or methylated forms in plasma, and is degraded and metabolized to conjugated forms of caffeic acid, ferulic acid and m-coumaric acid

Rosmarinic acid (RA) is contained in various Lamiaceae herbs used commonly as culinary herbs. Although RA has various potent physiological actions, little is known on its bioavailability. We therefore investigated the absorption and metabolism of orally administered RA in rats. After being deprived of food for 12 h, RA (50 mg/kg body weight) or deionized water was administered orally to rats. Blood samples were collected from a cannula inserted in the femoral artery before and at designated time intervals after administration of RA. Urine excreted within 0 to 8 h and 8 to 18 h post-administration was also collected. RA and its related metabolites in plasma and urine were measured by LC-MS after treatment with sulfatase and/or beta-glucuronidase. RA, mono-methylated RA (methyl-RA) and m-coumaric acid (COA) were detected in plasma, with peak concentrations being reached at 0.5, 1 and 8 h after RA administration, respectively. RA, methyl-RA, caffeic acid (CAA), ferulic acid (FA) and COA were detected in urine after RA administration. These components in plasma and urine were present predominantly as conjugated forms such as glucuronide or sulfate. The percentage of the original oral dose of RA excreted in the urine within 18 h of administration as free and conjugated forms was 0.44 +/- 0.21% for RA, 1.60 +/- 0.74% for methyl-RA, 1.06 +/- 0.35% for CAA, 1.70 +/- 0.45% for FA and 0.67 +/- 0.29% for COA. Approximately 83% of the total amount of these metabolites was excreted in the period 8 to 18 h after RA administration. These results suggest that RA was absorbed and metabolized as conjugated and/or methylated forms, and that the majority of RA absorbed was degraded into conjugated and/or methylated forms of CAA, FA and COA before being excreted gradually in the urine.