Stiffness, working stroke, and force of single-myosin molecules in skeletal muscle: elucidation of these mechanical properties via nonlinear elasticity evaluation

In muscles, the arrays of skeletal myosin molecules interact with actin filaments and continuously generate force at various contraction speeds. Therefore, it is crucial for myosin molecules to generate force collectively and minimize the interference between individual myosin molecules. Knowledge of the elasticity of myosin molecules is crucial for understanding the molecular mechanisms of muscle contractions because elasticity directly affects the working and drag (resistance) force generation when myosin molecules are positively or negatively strained. The working stroke distance is also an important mechanical property necessary for elucidation of the thermodynamic efficiency of muscle contractions at the molecular level. In this review, we focus on these mechanical properties obtained from single-fiber and single-molecule studies and discuss recent findings associated with these mechanical properties. We also discuss the potential molecular mechanisms associated with reduction of the drag effect caused by negatively strained myosin molecules.     

Room-temperature fabrication of transparent flexible thin-film transistors using amorphous oxide semiconductors

Transparent electronic devices formed on flexible substrates are expected to meet emerging technological demands where silicon-based electronics cannot provide a solution. Examples of active flexible applications include paper displays and wearable computers. So far, mainly flexible devices based on hydrogenated amorphous silicon (a-Si:H) and organic semiconductors have been investigated. However, the performance of these devices has been insufficient for use as transistors in practical computers and current-driven organic light-emitting diode displays. Fabricating high-performance devices is challenging, owing to a trade-off between processing temperature and device performance. Here, we propose to solve this problem by using a novel semiconducting material--namely, a transparent amorphous oxide semiconductor from the In-Ga-Zn-O system (a-IGZO)--for the active channel in transparent thin-film transistors (TTFTs). The a-IGZO is deposited on polyethylene terephthalate at room temperature and exhibits Hall effect mobilities exceeding 10 cm2 V(-1) s(-1), which is an order of magnitude larger than for hydrogenated amorphous silicon. TTFTs fabricated on polyethylene terephthalate sheets exhibit saturation mobilities of 6-9 cm2 V(-1) s(-1), and device characteristics are stable during repetitive bending of the TTFT sheet.     

Biased biological functions of horizontally transferred genes in prokaryotic genomes

Horizontal gene transfer is one of the main mechanisms contributing to microbial genome diversification. To clarify the overall picture of interspecific gene flow among prokaryotes, we developed a new method for detecting horizontally transferred genes and their possible donors by Bayesian inference with training models for nucleotide composition. Our method gives the average posterior probability (horizontal transfer index) for each gene sequence, with a low horizontal transfer index indicating recent horizontal transfer. We found that 14% of open reading frames in 116 prokaryotic complete genomes were subjected to recent horizontal transfer. Based on this data set, we quantitatively determined that the biological functions of horizontally transferred genes, except mobile element genes, are biased to three categories: cell surface, DNA binding and pathogenicity-related functions. Thus, the transferability of genes seems to depend heavily on their functions.     

Plant sesquiterpenes induce hyphal branching in arbuscular mycorrhizal fungi

Arbuscular mycorrhizal (AM) fungi form mutualistic, symbiotic associations with the roots of more than 80% of land plants. The fungi are incapable of completing their life cycle in the absence of a host root. Their spores can germinate and grow in the absence of a host, but their hyphal growth is very limited. Little is known about the molecular mechanisms that govern signalling and recognition between AM fungi and their host plants. In one of the first stages of host recognition, the hyphae of AM fungi show extensive branching in the vicinity of host roots before formation of the appressorium, the structure used to penetrate the plant root. Host roots are known to release signalling molecules that trigger hyphal branching, but these branching factors have not been isolated. Here we have isolated a branching factor from the root exudates of Lotus japonicus and used spectroscopic analysis and chemical synthesis to identify it as a strigolactone, 5-deoxy-strigol. Strigolactones are a group of sesquiterpene lactones, previously isolated as seed-germination stimulants for the parasitic weeds Striga and Orobanche. The natural strigolactones 5-deoxy-strigol, sorgolactone and strigol, and a synthetic analogue, GR24, induced extensive hyphal branching in germinating spores of the AM fungus Gigaspora margarita at very low concentrations.     

Dominant role of the niche in melanocyte stem-cell fate determination

Stem cells which have the capacity to self-renew and generate differentiated progeny are thought to be maintained in a specific environment known as a niche. The localization of the niche, however, remains largely obscure for most stem-cell systems. Melanocytes (pigment cells) in hair follicles proliferate and differentiate closely coupled to the hair regeneration cycle. Here we report that stem cells of the melanocyte lineage can be identified, using Dct-lacZ transgenic mice, in the lower permanent portion of mouse hair follicles throughout the hair cycle. It is only the population in this region that fulfils the criteria for stem cells, being immature, slow cycling, self-maintaining and fully competent in regenerating progeny on activation at early anagen (the growing phase of hair follicles). Induction of the re-pigmentation process in K14-steel factor transgenic mice demonstrates that a portion of amplifying stem-cell progeny can migrate out from the niche and retain sufficient self-renewing capability to function as stem cells after repopulation into vacant niches. Our data indicate that the niche has a dominant role in the fate determination of melanocyte stem-cell progeny.     

Crystal structure of a human membrane protein involved in cysteinyl leukotriene biosynthesis

The cysteinyl leukotrienes, namely leukotriene (LT)C4 and its metabolites LTD4 and LTE4, the components of slow-reacting substance of anaphylaxis, are lipid mediators of smooth muscle constriction and inflammation, particularly implicated in bronchial asthma. LTC4 synthase (LTC4S), the pivotal enzyme for the biosynthesis of LTC4 (ref. 10), is an 18-kDa integral nuclear membrane protein that belongs to a superfamily of membrane-associated proteins in eicosanoid and glutathione metabolism that includes 5-lipoxygenase-activating protein, microsomal glutathione S-transferases (MGSTs), and microsomal prostaglandin E synthase 1 (ref. 13). LTC4S conjugates glutathione to LTA4, the endogenous substrate derived from arachidonic acid through the 5-lipoxygenase pathway. In contrast with MGST2 and MGST3 (refs 15, 16), LTC4S does not conjugate glutathione to xenobiotics. Here we show the atomic structure of human LTC4S in a complex with glutathione at 3.3 A resolution by X-ray crystallography and provide insights into the high substrate specificity for glutathione and LTA4 that distinguishes LTC4S from other MGSTs. The LTC4S monomer has four transmembrane alpha-helices and forms a threefold symmetric trimer as a unit with functional domains across each interface. Glutathione resides in a U-shaped conformation within an interface between adjacent monomers, and this binding is stabilized by a loop structure at the top of the interface. LTA4 would fit into the interface so that Arg 104 of one monomer activates glutathione to provide the thiolate anion that attacks C6 of LTA4 to form a thioether bond, and Arg 31 in the neighbouring monomer donates a proton to form a hydroxyl group at C5, resulting in 5(S)-hydroxy-6(R)-S-glutathionyl-7,9-trans-11,14-cis-eicosatetraenoic acid (LTC4). These findings provide a structural basis for the development of LTC4S inhibitors for a proinflammatory pathway mediated by three cysteinyl leukotriene ligands whose stability and potency are different and by multiple cysteinyl leukotriene receptors whose functions may be non-redundant.     

ABCB6 is dispensable for erythropoiesis and specifies the new blood group system Langereis

The human ATP-binding cassette (ABC) transporter ABCB6 has been described as a mitochondrial porphyrin transporter essential for heme biosynthesis, but it is also suspected to contribute to anticancer drug resistance, as do other ABC transporters located at the plasma membrane. We identified ABCB6 as the genetic basis of the Lan blood group antigen expressed on red blood cells but also at the plasma membrane of hepatocellular carcinoma (HCC) cells, and we established that ABCB6 encodes a new blood group system (Langereis, Lan). Targeted sequencing of ABCB6 in 12 unrelated individuals of the Lan(-) blood type identified 10 different ABCB6 null mutations. This is the first report of deficient alleles of this human ABC transporter gene. Of note, Lan(-) (ABCB6(-/-)) individuals do not suffer any clinical consequences, although their deficiency in ABCB6 may place them at risk when determining drug dosage.     

Improved molecular replacement by density- and energy-guided protein structure optimization

Molecular replacement procedures, which search for placements of a starting model within the crystallographic unit cell that best account for the measured diffraction amplitudes, followed by automatic chain tracing methods, have allowed the rapid solution of large numbers of protein crystal structures. Despite extensive work, molecular replacement or the subsequent rebuilding usually fail with more divergent starting models based on remote homologues with less than 30% sequence identity. Here we show that this limitation can be substantially reduced by combining algorithms for protein structure modelling with those developed for crystallographic structure determination. An approach integrating Rosetta structure modelling with Autobuild chain tracing yielded high-resolution structures for 8 of 13 X-ray diffraction data sets that could not be solved in the laboratories of expert crystallographers and that remained unsolved after application of an extensive array of alternative approaches. We estimate that the new method should allow rapid structure determination without experimental phase information for over half the cases where current methods fail, given diffraction data sets of better than 3.2?? resolution, four or fewer copies in the asymmetric unit, and the availability of structures of homologous proteins with >20% sequence identity.     

一种在RTL测试模式生成中验证断言再用的方法

在对设计的功能验证中,断言常被用于检测设计错误.针对制造业的测试模式生成,提出了在寄存器传输层(RTL)用于无扫描设计的断言再用方法.这种方法减少了顺序自动测试码生成程序(ATPG)的搜索空间,因而能加快测试生成过程,增加故障覆盖率.通过实例分析,证明了该方法的可行性和效果.