Structural determinants for regulation of phosphodiesterase by a G protein at 2.0 A

A multitude of heptahelical receptors use heterotrimeric G proteins to transduce signals to specific effector target molecules. The G protein transducin, Gt, couples photon-activated rhodopsin with the effector cyclic GMP phosophodiesterase (PDE) in the vertebrate phototransduction cascade. The interactions of the Gt alpha-subunit (alpha(t)) with the inhibitory PDE gamma-subunit (PDEgamma) are central to effector activation, and also enhance visual recovery in cooperation with the GTPase-activating protein regulator of G-protein signalling (RGS)-9 (refs 1-3). Here we describe the crystal structure at 2.0 A of rod transducin alpha x GDP x AlF4- in complex with the effector molecule PDEgamma and the GTPase-activating protein RGS9. In addition, we present the independently solved crystal structures of the RGS9 RGS domain both alone and in complex with alpha(t/i1) x GDP x AlF4-. These structures reveal insights into effector activation, synergistic GTPase acceleration, RGS9 specificity and RGS activity. Effector binding to a nucleotide-dependent site on alpha(t) sequesters PDEgamma residues implicated in PDE inhibition, and potentiates recruitment of RGS9 for hydrolytic transition state stabilization and concomitant signal termination.     

Localization of the receptor-binding protein adhesin at the tip of the bacterial pilus

Strains of the bacterium Escherichia coli that cause infections of the human urinary tract produce so-called Pap-pili, which are hair-like appendages consisting of about 10(3) helically arranged subunits of the protein PapA. These pili mediate binding to digalactoside-containing glycolipids present on the epithelial cells which line the urinary tract. Recently, it has been suggested that three proteins, PapE, PapF and PapG, are responsible for this binding. In the absence of PapA, non-piliated bacteria are formed which nonetheless exhibit binding, showing that the bulk of the pilus is not essential for binding. Although pili can form without PapF and PapG, such pili are unable to bind to the digalactoside. The protein PapG mediates binding specificity in trans-complementation experiments, so this protein is the digalactoside-specific adhesin. Using immuno-electron microscopy we have found that Pap-pili are heteropolymers composed of the major pilin, PapA, the minor pilins, PapE and PapF, and the adhesin, PapG. The last three proteins are located at the tip of the pilus.     

DNA sequence determinants of CAP-induced bending and protein binding affinity

The sites of DNA bending induced by binding catabolite activator protein are identified and shown to coincide with positions where DNA grooves face the protein. The bendability of DNA with different sequences at these bend centres parallels the bending preference of the sequences in nucleosomal DNA. Anisotropic DNA bendability significantly affects the structure and strength of regulatory protein-DNA complexes.     

Adherens junction protein nectin-4 is the epithelial receptor for measles virus

Measles virus is an aerosol-transmitted virus that affects more than 10 million children each year and accounts for approximately 120,000 deaths. Although it was long believed to replicate in the respiratory epithelium before disseminating, it was recently shown to infect initially macrophages and dendritic cells of the airways using signalling lymphocytic activation molecule family member 1 (SLAMF1; also called CD150) as a receptor. These cells then cross the respiratory epithelium and transport the infection to lymphatic organs where measles virus replicates vigorously. How and where the virus crosses back into the airways has remained unknown. On the basis of functional analyses of surface proteins preferentially expressed on virus-permissive human epithelial cell lines, here we identify nectin-4 (ref. 8; also called poliovirus-receptor-like-4 (PVRL4)) as a candidate host exit receptor. This adherens junction protein of the immunoglobulin superfamily interacts with the viral attachment protein with high affinity through its membrane-distal domain. Nectin-4 sustains measles virus entry and non-cytopathic lateral spread in well-differentiated primary human airway epithelial sheets infected basolaterally. It is downregulated in infected epithelial cells, including those of macaque tracheae. Although other viruses use receptors to enter hosts or transit through their epithelial barriers, we suggest that measles virus targets nectin-4 to emerge in the airways. Nectin-4 is a cellular marker of several types of cancer, which has implications for ongoing measles-virus-based clinical trials of oncolysis.     

关于S-系的局部化

设S是幺半群,借助环与模范畴中的方法,讨论了半群S-系局部化的若干性质得到了S-系局部化的泛性质,并证明了T-1S的素理想和S中与T不相交的理想有一个保序的双射T-1P(→)P.     

关于半群的局部化

局部化是交换代数中的重要研究方法．将局部化概念推广到交换半群S上,得到了S上若干局部性质,这对用局部化方法研究半群很有意义．     

绿色荧光蛋白基因在牦牛乳腺上皮细胞中表达的研究

从牦牛乳腺采集组织, 并通过胶原酶消化法和胰蛋白酶消化法相结合在体外成功分离、纯化到了牦牛乳腺上皮细胞. 通过观察, 具有明显的上皮细胞特征, 而且符合一般细胞的生长规律. 通过脂质体介导法将携带有绿色荧光蛋白的外源基因转染进乳腺上皮细胞中, 在荧光显微镜下检测到了绿色荧光蛋白基因的表达.     

Activation of chloride channels in normal and cystic fibrosis airway epithelial cells by multifunctional calcium/calmodulin-dependent protein kinase.

Cystic fibrosis is associated with defective regulation of apical membrane chloride channels in airway epithelial cells. These channels in normal cells are activated by cyclic AMP-dependent protein kinase and protein kinase C. In cystic fibrosis these kinases fail to activate otherwise normal Cl- channels. But Cl- flux in cystic fibrosis cells, as in normal cells, can be activated by raising intracellular Ca2+ (refs 5-10). We report here whole-cell patch clamp studies of normal and cystic fibrosis-derived airway epithelial cells showing that Cl- channel activation by Ca2+ is mediated by multifunctional Ca2+/calmodulin-dependent protein kinase. We find that intracellular application of activated kinase and ATP activates a Cl- current similar to that activated by a Ca2+ ionophore, that peptide inhibitors of either the kinase or calmodulin block Ca2(+)-dependent activation of Cl- channels, and that a peptide inhibitor of protein kinase C does not block Ca2(+)-dependent activation. Ca2+/calmodulin activation of Cl- channels presents a pathway with therapeutic potential for circumventing defective regulation of Cl- channels in cystic fibrosis.     

试论第三方物流企业的本土化战略

经济的全球化,推动了工商企业实施本土化战略,物流的本土化是一种服务的延伸,是工商企业占领市场的关键。国际第三方物流企业抓住机遇建立覆盖整个目标区域的网络。通过市场营销本土化、人力资源本土化和企业文化本土化措施,实施本土化战略,解决“差异化”和“成本管理”问题,以获得市场份额,实现第三方物流企业与货主企业在供应链上的“双赢”。     

型A半群的局部化

证明了任一型A半群在其幂等元半格上的局部化存在且在同构意义下唯一,从而将局部化推广到型A半群上,接着证明了该局部化就是它的最大可消幺半群同态像,并由此导出了型A半群的最小可消幺半群同余的一个刻画．     

Mapping determinants of human gene expression by regional and genome-wide association

To study the genetic basis of natural variation in gene expression, we previously carried out genome-wide linkage analysis and mapped the determinants of approximately 1,000 expression phenotypes. In the present study, we carried out association analysis with dense sets of single-nucleotide polymorphism (SNP) markers from the International HapMap Project. For 374 phenotypes, the association study was performed with markers only from regions with strong linkage evidence; these regions all mapped close to the expressed gene. For a subset of 27 phenotypes, analysis of genome-wide association was performed with >770,000 markers. The association analysis with markers under the linkage peaks confirmed the linkage results and narrowed the candidate regulatory regions for many phenotypes with strong linkage evidence. The genome-wide association analysis yielded highly significant results that point to the same locations as the genome scans for about 50% of the phenotypes. For one candidate determinant, we carried out functional analyses and confirmed the variation in cis-acting regulatory activity. Our findings suggest that association studies with dense SNP maps will identify susceptibility loci or other determinants for some complex traits or diseases.     

Structural determinants for GoLoco-induced inhibition of nucleotide release by Galpha subunits

Heterotrimeric G-proteins bind to cell-surface receptors and are integral in transmission of signals from outside the cell. Upon activation of the Galpha subunit by binding of GTP, the Galpha and Gbetagamma subunits dissociate and interact with effector proteins for signal transduction. Regulatory proteins with the 19-amino-acid GoLoco motif can bind to Galpha subunits and maintain G-protein subunit dissociation in the absence of Galpha activation. Here we describe the structural determinants of GoLoco activity as revealed by the crystal structure of Galpha(i1) GDP bound to the GoLoco region of the 'regulator of G-protein signalling' protein RGS14. Key contacts are described between the GoLoco motif and Galpha protein, including the extension of GoLoco's highly conserved Asp/Glu-Gln-Arg triad into the nucleotide-binding pocket of Galpha to make direct contact with the GDP alpha- and beta-phosphates. The structural organization of the GoLoco Galpha(i1) complex, when combined with supporting data from domain-swapping experiments, suggests that the Galpha all-helical domain and GoLoco-region carboxy-terminal residues control the specificity of GoLoco Galpha interactions.