Novel emission properties of melem caused by the heavy metal effect of lanthanides(III) in a LB film.

A novel emissive molecular system is constructed by the intercalation of the fluorophore melem (triamino-tri-s-triazine) within a Langmuir-Blodgett (LB) film of stearic acid with the periodic arrangement of lanthanides (Ln(III)), mainly Pr(III) with supporting of Eu(III). From emission spectra, decay curves, quantum yields and XPS measurements, it is clarified that the external heavy metal effect of Pr(III) on melem is much stronger in the film than in the bulk solid state, resulting in producing an unusual triplet state of melem. The triplet state of melem in the LB film donates the excitation energy to Pr(III) in the LB film, which is completely different from the energy transfer pathway of Pr-melem complex in the solid state through the singlet state of melem.     

The criteria for biomass partitioning of the current shoot: water transport versus mechanical support

In this study, we determine the theoretical criteria for biomass partitioning into the leaf and stem of the current shoot, using two quantitative models. The water transport model, based on the biochemical model of CO(2) assimilation, predicts the relationship between the water transport capacity per biomass investment in the stem (stem mass specific conductivity) and the partitioning of biomass that maximizes shoot productivity. The mechanical support model, based on Euler's buckling formula, predicts the relationship between the mechanical strength per biomass investment in the stem (the inverse relationship of stem mass density) and the partitioning of biomass to avoid mechanical failures such as lodging. These models predict the stem properties of mass specific conductivity and stem mass density that result in optimum partitioning just sufficient to provide adequate water transport and static mechanical support. In reality, the stem properties of plants differ from those predicted for optimum partitioning: the partitioning of biomass in the current shoot of both angiosperms and gymnosperms is mainly governed by the mechanical support criterion, although gymnosperms are probably more affected by the water transport criterion. This tendency is supported by actual measurements of biomass partitioning in plants.     

Bacillus subtilis LmrA is a repressor of the lmrAB and yxaGH operons: identification of its binding site and functional analysis of lmrB and yxaGH

The Bacillus subtilis lmrAB operon is involved in multidrug resistance. LmrA is a repressor of its own operon, while LmrB acts as a multidrug efflux transporter. LmrA was produced in Escherichia coli cells and was shown to bind to the lmr promoter region, in which an LmrA-binding site was identified. Genome-wide screening involving DNA microarray analysis allowed us to conclude that LmrA also repressed yxaGH, which was not likely to contribute to the multidrug resistance. LmrA bound to a putative yxaGH promoter region, in which two tandem LmrA-binding sites were identified. The LmrA regulon was thus determined to comprise lmrAB and yxaGH. All three LmrA-binding sites contained an 18-bp consensus sequence, TAGACCRKTCWMTATAWT, which could play an important role in LmrA binding.     

Functional regulation of FEZ1 by the U-box-type ubiquitin ligase E4B contributes to neuritogenesis

E4B (also known as UFD2a) is a mammalian homolog of Saccharomyces cerevisiae Ufd2, which was originally described as a ubiquitin chain assembly factor (E4). E4B is a U-box-type ubiquitin-protein isopeptide ligase (E3) and likely functions as either an E3 or an E4. With a yeast two-hybrid screen, we have now identified FEZ1 (fasciculation and elongation protein zeta 1) as a protein that interacts with E4B. FEZ1 is implicated in neuritogenesis when phosphorylated by protein kinase Czeta (PKCzeta). Interaction between E4B and FEZ1 in mammalian cells was enhanced by coexpression of constitutively active PKCzeta. E4B mediated the polyubiquitylation of FEZ1 but did not affect its intracellular stability, suggesting that such modification of FEZ1 is not a signal for its proteolysis. Polyubiquitylation of FEZ1 by E4B required Lys(27) of ubiquitin. Expression of a dominant-negative mutant of E4B in rat pheochromocytoma PC12 cells resulted in inhibition of neurite extension induced either by nerve growth factor or by coexpression of FEZ1 and constitutively active PKCzeta. These findings indicate that E4B serves as a ubiquitin ligase for FEZ1 and thereby regulates its function but not its degradation.     

Gene cloning and overproduction of an aminopeptidase from Streptomyces septatus TH-2, and comparison with a calcium-activated enzyme from Streptomyces griseus

An aminopeptidase secreted from Streptomyces septatus TH-2 (SSAP) was identified as a heat stable enzyme, and the Ssap gene was cloned and sequenced. The primary structure of SSAP showed 71% identity with that of a Streptomyces griseus aminopeptidase (SGAP), however, it lacked a unique calcium binding site. The recombinant SSAP was overexpressed in the culture supernatant of Escherichia coli harboring pET-KmS2. A comparison of recombinant SSAP and SGAP showed that both enzymes are different in terms of modulation by calcium and substrate specificity. The activity of SSAP was not modulated by calcium, while SGAP is a calcium-activated enzyme. SSAP catalyzed the hydrolysis of L-Lys-pNA efficiently whereas the reaction rate for L-Lys-pNA hydrolysis of SGAP was significantly low. Furthermore, in SGAP, the presence of Ca2+ decreased the reaction rate of L-Lys-pNA hydrolysis. SSAP also had different pKas s of reaction from that of SGAP, although almost all the residues which compose the active site were conserved in both enzymes. This result indicates that SSAP has a different environment of substrate binding and active sites from those of SGAP.     

Involvement of ERK, a MAP kinase, in the production of TGF-beta by macrophages treated with liposomes composed of phosphatidylserine

We have already reported that TGF-beta could be involved in the inhibitory effects of negatively charged liposomes composed of phosphatidylserine (PS-liposome) on the production of nitric oxide (NO) by mouse peritoneal macrophages stimulated with LPS [Biochem. Biophys. Res. Commun. 281 (2001) 614]. In this paper, we explored the mechanism by which PS-liposomes promote the production of TGF-beta and the involvement of MAP kinases. When macrophages were treated with PS-liposomes, extracellular signal-regulated kinase (ERK), a member of MAP kinase superfamily, was activated quickly and potently. However, no activation was observed with p38 MAP kinase. TGF-beta production was completely inhibited by U0126, a specific inhibitor for ERK. Furthermore, TGF-beta neutralizing antibody and U0126 decreased the inhibitory effect of PS-liposomes on NO production by macrophages. These findings suggested that TGF-beta is the factor produced by PS-liposomes that suppresses production of NO, and the ERK signaling pathway is intimately involved in TGF-beta production by macrophages following treatment with PS-liposomes.     

Human NTH1 physically interacts with p53 and proliferating cell nuclear antigen

Thymine glycol (Tg) is one of predominant oxidative DNA lesions caused by ionizing radiation and other oxidative stresses. Human NTH1 is a bifunctional enzyme with DNA glycosylase and AP lyase activities and removes Tg as the first step of base excision repair (BER). We have searched for the factors interacting with NTH1 by using a pull-down assay and found that GST-NTH1 fusion protein precipitates proliferating cell nuclear antigen (PCNA) and p53 as well as XPG from human cell-free extracts. GST-NTH1 also bound to recombinant FLAG-tagged XPG, PCNA, and (His)6-tagged p53 proteins, indicating direct protein-protein interaction between those proteins. Furthermore, His-p53 and FLAG-XPG, but not PCNA, stimulated the Tg DNA glycosylase/AP lyase activity of GST-NTH1 or NTH1. These results provide an insight into the positive regulation of BER reaction and also suggest a possible linkage between BER of Tg and other cellular mechanisms.     

Binding of alpha1-acid glycoprotein to membrane results in a unique structural change and ligand release

Alpha(1)-acid glycoprotein (AGP) consists of 183 amino acid residues and 5 carbohydrate chains and binds to basic and neutral drugs as well as steroid hormones. We investigated the structural properties and ligand-binding capacity of AGP under mild acidic conditions and its interactions with liposomes prepared from neutral or anionic lipids and the neutral drug, progesterone. Interestingly, AGP had a unique structure at pH 4.5, at which the tertiary structure changed, whereas the secondary structure remained intact. Furthermore, the binding capacity of AGP for progesterone did not significantly change under these conditions. It was also observed that AGP was strongly bound to the anionic membrane at pH 4.5, forming an alpha-helix-rich structure from the original beta-sheet-rich structure, which significantly decreased the binding capacity of AGP for progesterone. The structural transitions as well as the membrane binding were suppressed by adding NaCl. These results indicate that AGP has a unique structure on the membrane surface under mild acidic conditions. The conformational change induces binding to the membrane aided by electrostatic interaction, and AGP subsequently takes on a predominantly alpha-helical conformation.