Effects of Soluble CD4 on Simian Immunodeficiency Virus Infection of CD4-Positive and CD4-Negative Cells

A soluble form of the CD4 receptor (sCD4) can either enhance or inhibit the infection of cells by simian immunodeficiency virus (SIV) and human immunodeficiency virus. We investigated the basis for these varying effects by studying the entry of three SIV isolates into CD4-positive and CD4-negative cells expressing different chemokine receptors. Infection of CD4-negative cells depended upon the viral envelope glycoproteins and upon the chemokine receptor, with CCR5 and gpr15 being more efficient than STRL33. Likewise, enhancement of infection by sCD4 was observed when CCR5- and gpr15-expressing target cells were used but not when those expressing STRL33 were used. The sCD4-mediated enhancement of virus infection of CD4-negative, CCR5-positive cells was related to the sCD4-induced increase in binding of the viral gp120 envelope glycoprotein to CCR5. Inhibitory effects of sCD4 could largely be explained by competition for virus attachment to cellular CD4 rather than other detrimental effects on virus infectivity (e.g., disruption of the envelope glycoprotein spike). Consistent with this, the sCD4-activated SIV envelope glycoprotein intermediate on the virus was long-lived. Thus, the net effect of sCD4 on SIV infectivity appears to depend upon the degree of enhancement of chemokine receptor binding and upon the efficiency of competition for cellular CD4.     

Combining genetic non-invasive sampling with spatially explicit capture-recapture models for density estimation of a patchily distributed small mammal

Estimating the size of animal populations is essential for understanding the demography and conservation status of species. Genetic Non-Invasive Sampling (gNIS) combined with Spatially Explicit Capture-Recapture (SECR) modelling may provide a practical tool to obtain such estimates. Here, we evaluate for the first time the potential and limitations of this approach to estimate population densities for small mammals inhabiting patchily distributed habitats, focusing on the endemic Iberian Cabrera vole (Microtus cabrerae). Using 11 highly polymorphic microsatellites and two sex-linked introns, we compared population estimates in November/December 2011 based on live-trapping and gNIS and assessed the impact of distinct consensus criteria to differentiate unique genotypes. Live-trapping over 21 days captured 31 individuals, while gNIS over 5 days recorded 65–69 individuals. SECR models indicated that individual detectability was positively affected by live-trapping capture success on the previous occasion, while for gNIS, it was mainly affected by genotyping success rates and patch size. Live-trapping produced the lowest density estimates (mean ± SE) of 16.6?±?3.2 individuals per hectare of suitable habitat (ind/ha). Estimates based on gNIS were higher and varied slightly between 25.2?±?4.0 and 28.8?±?4.5 ind/ha depending on assuming one or two genotyping errors, respectively, when differentiating individual genetic profiles. Results suggest that live-trapping underestimated the vole population, while the larger number of individuals detected through gNIS allowed better estimates with lower field effort. Overall, we suggest that gNIS combined with SECR models provides an effective tool to estimate small mammal population densities in fragmented habitats.     

Improving the selectivity of acyclic nucleoside analogues as inhibitors of human mitochondrial thymidine kinase: replacement of a triphenylmethoxy moiety with substituted amines and carboxamides

Two series of analogues of the novel human mitochondrial thymidine kinase inhibitor 1-[(Z)-4-(triphenylmethoxy)-2-butenyl]thymine were synthesized by replacing the triphenylmethoxy moiety by a variety of substituted amines and carboxamides. In all the cases, the selectivity against the mitochondrial enzyme was either maintained or improved, and several derivatives were almost as potent as the parent compound. A molecular model was built that can account for the observed selectivities.     

Beta 2-microglobulin-deficient background ameliorates lethal phenotype of the TGF-beta 1 null mouse.

TGF-beta 1 null (TGF-beta1-/-) mice die at 3-4 wk of age and show an autoimmune inflammatory phenotype associated with enhanced expression of both class I and II MHC molecules. To determine the role of MHC class I Ags in the autoimmune manifestations and the inflammation observed in TGF-beta 1-/- mice, we generated TGF-beta 1-/- mice in the genetic background of beta 2-microglobulin deficiency (beta 2M-/-). TGF-beta 1-/-;beta 2M-/- mice had improved survival compared with TGF-beta 1-/- mice. Histopathological examination showed less severe inflammation, especially in the heart, where Mac-2 reactive macrophages were significantly decreased as compared with TGF-beta 1-/- mice. In vivo depletion of CD8+ T cells in TGF-beta 1-/- mice confirmed suppression of inflammation and reduction in the severity of the wasting syndrome. MHC class II mRNA expression in TGF-beta 1-/-;beta 2M-/- mice was also lower than that in TGF-beta 1-/- mice, suggesting reduced systemic inflammation. Autoimmune response as judged by serum Ab titers to ssDNA and 16/6 Id and by immune complex deposits in kidney was reduced in TGF-beta 1-/-;beta 2M-/- mice, when compared with that in TGF-beta 1-/- mice. Our data thus indicate that MHC class I molecules influence the development of the autoimmunity and the inflammation seen in TGF-beta 1-/- mice and CD8+ T cells may have a contribution to the inflammation in TGF-beta 1-/- mice.     

Pyrite oxidation by thermophilic archaebacteria

Three species of thermophilic archaebacteria of the genera Sulfolobus (Sulfolobus acidocaldarius and S. solfataricus) and Acidianus (Acidianus brierleyi) were tested for their ability to oxidize pyrite and to grow autotrophically on pyrite, to explore their potential for use in coal desulfurization. Only A. brierleyi was able to oxidize and grow autotrophically on pyrite. Jarosite was formed during the pyrite oxidation, resulting in the precipitation of sulfate and iron. The medium composition affected the extent of jarosite formation.     

Identification and changes in activity of five thymidine kinase forms during the cell cycle of Physarum polycephalum

Five forms of thymidine kinase have been identified on isoelectric focusing gels of Physarum polycephalum supernatants. Their isoelectric points are 5.9, 6.4, 6.7, 6.9 and 7.1. All are inhibited by deoxythymidine 5′-triphosphate (dTTP). The activity of the pI 7.1 form does not change significantly during the cell cycle. The other four forms change in activity. About 1 h before metaphase the activity of the four more acidic forms is first detected. Their activity peaks during telophase, and by 1 h after metaphase there is a 50% decrease in activity of the 5.9 form. By 3 h after metaphase the activity of the 6.4 form has dropped more sharply than the activity of the 6.7 form. By 6 h after metaphase only the activity of the 6.9 form is present in significant amounts in addition to the 7.1 form. The activity of these new acidic forms probably accounts for the reported increase in total thymidine kinase activity during mitosis and early S phase.     

The effect of redox state on the folding free energy of azurin

 The unfolding of oxidized and reduced azurin by guanidine hydrochloride has been monitored by circular dichroism. Dilution experiments showed the unfolding to be reversible, and the equilibrium data have been interpreted in terms of a two-state model. The protein is stabilized by the strong metal binding in the native state, so that the folding free energy is as high as –52.2 kJ mol^–1 for the oxidized protein. The reduced protein is less stable, with a folding free energy of –40.0 kJ mol^–1. A thermodynamic cycle shows, as a consequence, that unfolded azurin has a reduction potential 0.13 V above that of the folded protein. This is explained by the bipyramidal site in the native fold stabilizing Cu(II) by a rack mechanism, with the same geometry being maintained in the Cu(I) form. In the unfolded protein, on the other hand, the coordination geometries are expected to differ for the two oxidation states, Cu(I) being stabilized by the cysteine thiol group in a linear or trigonal symmetry, whereas Cu(II) prefers oxygen ligands in a tetragonal geometry. Received: 15 January 1997 / Accepted: 3 April 1997