Characterization of bacterium isolated from the sediment at coastal area of Omura Bay in Japan and several biological activities of pigment produced by this isolate

Recently we discovered a bacterial strain (MS-02-063) that produces large amounts of red pigment from coastal area of Nagasaki Prefecture, Japan. Comparative 16S rDNA gene sequencing analysis revealed that strain MS-02-063 was phylogenetically closely related to gamma-proteobacterium Hahella sp. MBIC 3957 that produces prodigiosin. However, some physiological and biochemical differences between strain MS-02-063 and Hahella sp. MBIC 3957 were observed. The red pigment (RP-063) produced by this isolate was highly purified from the culture supernatant. It was speculated that RP-063 might be prodigiosin-like pigment in physical properties and biological activities such as antibacterial and cytotoxic activity. Antibacterial activity of RP-063 was examined by an agar dilution method. The results indicated that RP-063 showed antibacterial activity for specific for pathogenic gram-positive bacteria such as Staphylococcus aureus. The potency of antibacterial activity against S. aureus was nearly equal to those of tetracycline. Moreover, RP-063 showed inhibition of the superoxide generation by 12-O-tetradecanoylphorbol-13-acetate (TPA)-stimulated mouse macrophage RAW 264.7 cell line. Prodigiosin members have a wide variety of biological properties, including anticancer and antimalarial, etc. Especially, potent immunosuppressive properties have been reported for prodigiosin members with the mechanism of action different from that of the other well known immunosuppressors in atopic dermatitis therapy such as cyclosporin A, FK506 and rapamycin. It is suggested that RP-063 may be able to arrest the inflammation caused by superantigens secreted from S. aureus, which colonized skin on atopic dermatitis as well as suppression of activated lymphocyte proliferation and superoxide generation from leucocytes.     

Structural basis for Ca2+-regulated muscle relaxation at interaction sites of troponin with actin and tropomyosin

Troponin and tropomyosin on actin filaments constitute a Ca2+-sensitive switch that regulates the contraction of vertebrate striated muscle through a series of conformational changes within the actin-based thin filament. Troponin consists of three subunits: an inhibitory subunit (TnI), a Ca2+-binding subunit (TnC), and a tropomyosin-binding subunit (TnT). Ca2+-binding to TnC is believed to weaken interactions between troponin and actin, and triggers a large conformational change of the troponin complex. However, the atomic details of the actin-binding sites of troponin have not been determined. Ternary troponin complexes have been reconstituted from recombinant chicken skeletal TnI, TnC, and TnT2 (the C-terminal region of TnT), among which only TnI was uniformly labelled with 15N and/or 13C. By applying NMR spectroscopy, the solution structures of a "mobile" actin-binding domain (approximately 6.1 kDa) in the troponin ternary complex (approximately 52 kDa) were determined. The mobile domain appears to tumble independently of the core domain of troponin. Ca2+-induced changes in the chemical shift and line shape suggested that its tumbling was more restricted at high Ca2+ concentrations. The atomic details of interactions between actin and the mobile domain of troponin were defined by docking the mobile domain into the cryo-electron microscopy (cryo-EM) density map of thin filament at low [Ca2+]. This allowed the determination of the 3D position of residue 133 of TnI, which has been an important landmark to incorporate the available information. This enabled unique docking of the entire globular head region of troponin into the thin filament cryo-EM map at a low Ca2+ concentration. The resultant atomic model suggests that troponin interacted electrostatically with actin and caused the shift of tropomyosin to achieve muscle relaxation. An important feature is that the coiled-coil region of troponin pushed tropomyosin at a low Ca2+ concentration. Moreover, the relationship between myosin and the mobile domain on actin filaments suggests that the latter works as a fail-safe latch.     

Altered microtubule dynamics by expression of modified alpha-tubulin protein causes right-handed helical growth in transgenic Arabidopsis plants

The proper organization of cortical microtubule arrays is essential for anisotropic growth in plants but how distinct array patterns are formed is not understood. Here, we report a relationship between microtubule dynamics and array organization using transgenic plants expressing modified tubulins. When green fluorescent protein (GFP) or a hemaglutinin epitope tag was fused to the N-terminus of tubulins and expressed in Arabidopsis plants, these tubulins were incorporated into microtubules along with endogenous tubulins. Plants expressing the modified beta-tubulins were phenotypically normal and possessed transversely oriented cortical arrays in the epidermal cells of the root elongation zone; however, the expression of modified alpha-tubulins caused right-handed helical growth, increased trichome branching, and a shallow left-handed (S-form) helical array organization. In cells expressing the modified alpha-tubulins, microtubule dynamicity was suppressed and polymerization was promoted, and GFP-EB1 (End Binding 1) labeled larger regions of the microtubule end more frequently, when compared with control cells. We propose that the N-terminal appendage introduced into alpha-tubulin inhibits GTP hydrolysis, thus producing polymerization-prone microtubules with an extended GTP cap. Consistent with this interpretation, plants expressing an alpha-tubulin mutated in the GTPase-activating domain exhibited similar microtubule properties, with regard to dynamics and the localization of GFP-EB1, and showed right-handed helical growth.     

Analysis of expressed sequence tags in prothallia of Adiantum capillus-veneris

The analysis of expressed sequences from a diverse set of plant species has fueled the increase in understanding of the complex molecular mechanisms underlying plant growth regulation. While representative data sets can be found for the major branches of plant evolution, fern species data are lacking. To further the availability of genetic information in pteridophytes, a normalized cDNA library of Adiantum capillus-veneris was constructed from prothallia grown under white light. A total of 10,420 expressed sequence tags (ESTs) were obtained and clustering of these sequences resulted in 7,100 nonredundant clusters. Of these, 1,608 EST clusters were found to be similar to sequences of known function and 1,092 EST clusters showed similarity to sequences of unknown function. Given the usefulness of Adiantum for developmental studies, the sequence data represented in this report stand to make a significant contribution to the understanding of plant growth regulation, particularly for pteridophytes.     

Regulation of isthmic Fgf8 signal by sprouty2

Fgf8 functions as an organizer at the mes/metencephalic boundary (isthmus). We showed that a strong Fgf8 signal activates the Ras-ERK signaling pathway to organize cerebellar differentiation. Sprouty2 is expressed in an overlapping manner to Fgf8, and is induced by Fgf8. Its function, however, is indicated to antagonize Ras-ERK signaling. Here, we show the regulation of Fgf8 signaling in relation to Sprouty2. sprouty2 expression was induced very rapidly by Fgf8b, but interfered with ERK activation. sprouty2 misexpression resulted in a fate change of the presumptive metencephalon to the mesencephalon. Misexpression of a dominant negative form of Sprouty2 augmented ERK activation, and resulted in anterior shift of the posterior border of the tectum. The results indicate that Fgf8 activates the Ras-ERK signaling pathway to differentiate the cerebellum, and that the hyper- or hypo-signaling of this pathway affects the fate of the brain vesicles. Sprouty2 may regulate the Fgf8-Ras-ERK signaling pathway for the proper regionalization of the metencephalon and mesencephalon.     

SMC proteins and chromosome mechanics: from bacteria to humans

Chromosome cohesion and condensation are essential prerequisites of proper segregation of genomes during mitosis and meiosis, and are supported by two structurally related protein complexes, cohesin and condensin, respectively. At the core of the two complexes lie members of the structural maintenance of chromosomes (SMC) family of ATPases. SMC proteins are also found in most bacterial and archaeal species, implicating the existence of an evolutionarily conserved theme of higher-order chromosome organization and dynamics. SMC dimers adopt a two-armed structure with an ATP-binding cassette (ABC)-like domain at the distal end of each arm. This article reviews recent work on the bacterial and eukaryotic SMC protein complexes, and discusses current understanding of how these uniquely designed protein machines may work at a mechanistic level. It seems most likely that the action of SMC proteins is highly dynamic and plastic, possibly involving a diverse array of intramolecular and intermolecular protein-protein interactions.