Crystal structure of a potassium ion transporter, TrkH

The TrkH/TrkG/KtrB proteins mediate K(+) uptake in bacteria and probably evolved from simple K(+) channels by multiple gene duplications or fusions. Here we present the crystal structure of a TrkH from Vibrio parahaemolyticus. TrkH is a homodimer, and each protomer contains an ion permeation pathway. A selectivity filter, similar in architecture to those of K(+) channels but significantly shorter, is lined by backbone and side-chain oxygen atoms. Functional studies showed that TrkH is selective for permeation of K(+) and Rb(+) over smaller ions such as Na(+) or Li(+). Immediately intracellular to the selectivity filter are an intramembrane loop and an arginine residue, both highly conserved, which constrict the permeation pathway. Substituting the arginine with an alanine significantly increases the rate of K(+) flux. These results reveal the molecular basis of K(+) selectivity and suggest a novel gating mechanism for this large and important family of membrane transport proteins.     

Functional genomics reveal that the serine synthesis pathway is essential in breast cancer

Cancer cells adapt their metabolic processes to drive macromolecular biosynthesis for rapid cell growth and proliferation. RNA interference (RNAi)-based loss-of-function screening has proven powerful for the identification of new and interesting cancer targets, and recent studies have used this technology in vivo to identify novel tumour suppressor genes. Here we developed a method for identifying novel cancer targets via negative-selection RNAi screening using a human breast cancer xenograft model at an orthotopic site in the mouse. Using this method, we screened a set of metabolic genes associated with aggressive breast cancer and stemness to identify those required for in vivo tumorigenesis. Among the genes identified, phosphoglycerate dehydrogenase (PHGDH) is in a genomic region of recurrent copy number gain in breast cancer and PHGDH protein levels are elevated in 70% of oestrogen receptor (ER)-negative breast cancers. PHGDH catalyses the first step in the serine biosynthesis pathway, and breast cancer cells with high PHGDH expression have increased serine synthesis flux. Suppression of PHGDH in cell lines with elevated PHGDH expression, but not in those without, causes a strong decrease in cell proliferation and a reduction in serine synthesis. We find that PHGDH suppression does not affect intracellular serine levels, but causes a drop in the levels of α-ketoglutarate, another output of the pathway and a tricarboxylic acid (TCA) cycle intermediate. In cells with high PHGDH expression, the serine synthesis pathway contributes approximately 50% of the total anaplerotic flux of glutamine into the TCA cycle. These results reveal that certain breast cancers are dependent upon increased serine pathway flux caused by PHGDH overexpression and demonstrate the utility of in vivo negative-selection RNAi screens for finding potential anticancer targets.     

An extremely primitive star in the Galactic halo

The early Universe had a chemical composition consisting of hydrogen, helium and traces of lithium; almost all other elements were subsequently created in stars and supernovae. The mass fraction of elements more massive than helium, Z, is known as 'metallicity'. A number of very metal-poor stars has been found, some of which have a low iron abundance but are rich in carbon, nitrogen and oxygen. For theoretical reasons and because of an observed absence of stars with Z?相似文献   

Glycosphingolipid synthesis requires FAPP2 transfer of glucosylceramide

The molecular machinery responsible for the generation of transport carriers moving from the Golgi complex to the plasma membrane relies on a tight interplay between proteins and lipids. Among the lipid-binding proteins of this machinery, we previously identified the four-phosphate adaptor protein FAPP2, the pleckstrin homology domain of which binds phosphatidylinositol 4-phosphate and the small GTPase ARF1. FAPP2 also possesses a glycolipid-transfer-protein homology domain. Here we show that human FAPP2 is a glucosylceramide-transfer protein that has a pivotal role in the synthesis of complex glycosphingolipids, key structural and signalling components of the plasma membrane. The requirement for FAPP2 makes the whole glycosphingolipid synthetic pathway sensitive to regulation by phosphatidylinositol 4-phosphate and ARF1. Thus, by coupling the synthesis of glycosphingolipids with their export to the cell surface, FAPP2 emerges as crucial in determining the lipid identity and composition of the plasma membrane.     

Retroelements and their impact on genome evolution and functioning

Retroelements comprise a considerable fraction of eukaryotic genomes. Since their initial discovery by Barbara McClintock in maize DNA, retroelements have been found in genomes of almost all organisms. First considered as a “junk DNA” or genomic parasites, they were shown to influence genome functioning and to promote genetic innovations. For this reason, they were suggested as an important creative force in the genome evolution and adaptation of an organism to altered environmental conditions. In this review, we summarize the up-to-date knowledge of different ways of retroelement involvement in structural and functional evolution of genes and genomes, as well as the mechanisms generated by cells to control their retrotransposition.     

Injection of adult neurospheres induces recovery in a chronic model of multiple sclerosis

Widespread demyelination and axonal loss are the pathological hallmarks of multiple sclerosis. The multifocal nature of this chronic inflammatory disease of the central nervous system complicates cellular therapy and puts emphasis on both the donor cell origin and the route of cell transplantation. We established syngenic adult neural stem cell cultures and injected them into an animal model of multiple sclerosis--experimental autoimmune encephalomyelitis (EAE) in the mouse--either intravenously or intracerebroventricularly. In both cases, significant numbers of donor cells entered into demyelinating areas of the central nervous system and differentiated into mature brain cells. Within these areas, oligodendrocyte progenitors markedly increased, with many of them being of donor origin and actively remyelinating axons. Furthermore, a significant reduction of astrogliosis and a marked decrease in the extent of demyelination and axonal loss were observed in transplanted animals. The functional impairment caused by EAE was almost abolished in transplanted mice, both clinically and neurophysiologically. Thus, adult neural precursor cells promote multifocal remyelination and functional recovery after intravenous or intrathecal injection in a chronic model of multiple sclerosis.     

Hermansky-Pudlak syndrome is caused by mutations in HPS4, the human homolog of the mouse light-ear gene

Hermansky-Pudlak syndrome (HPS) is a disorder of organelle biogenesis in which oculocutaneous albinism, bleeding and pulmonary fibrosis result from defects of melanosomes, platelet dense granules and lysosomes. HPS is common in Puerto Rico, where it is caused by mutations in the genes HPS1 and, less often, HPS3 (ref. 8). In contrast, only half of non-Puerto Rican individuals with HPS have mutations in HPS1 (ref. 9), and very few in HPS3 (ref. 10). In the mouse, more than 15 loci manifest mutant phenotypes similar to human HPS, including pale ear (ep), the mouse homolog of HPS1 (refs 13,14). Mouse ep has a phenotype identical to another mutant, light ear (le), which suggests that the human homolog of le is a possible human HPS locus. We have identified and found mutations of the human le homolog, HPS4, in a number of non-Puerto Rican individuals with HPS, establishing HPS4 as an important HPS locus in humans. In addition to their identical phenotypes, le and ep mutant mice have identical abnormalities of melanosomes, and in transfected melanoma cells the HPS4 and HPS1 proteins partially co-localize in vesicles of the cell body. In addition, the HPS1 protein is absent in tissues of le mutant mice. These results suggest that the HPS4 and HPS1 proteins may function in the same pathway of organelle biogenesis.     

Catalase activity among leptospires

Summary Catalase activity was measured by a quantitative method as an additional screening for discriminating between saprophytic and pathogenic leptospires. Results indicate that water-leptospires have little or no catalase activity.