An experimental and theoretical study of transient negative ions in Mg, Zn, Cd and Hg

A range of experimental and theoretical techniques have been applied to the study of transient negative ions (resonances) formed in electron scattering from the Group II metals Mg, Zn, Cd, and Hg at incident electron energies below the first ionization potential. A wealth of resonance structures have been observed and from the experimental observations and theoretical information, classifications are proposed for some of these negative ion states

Structure of HIV-1 reverse transcriptase in a complex with the non-nucleoside inhibitor α-APA R 95845 at 2.8 å resolution

AbstractBackground: HIV-1 reverse transcriptase (RT) is a multifunctional enzyme that copies the RNA genome of HIV-1 into DNA. It is a heterodimer composed of a 66 kDa (p66) and a 51 kDa (p51) subunit. HIV-1 RT is a crucial target for structure-based drug design, and potent inhibitors have been identified, whose efficacy, however, is limited by drug resistance.Results The crystal structure of HIV-1 RT in complex with the non-nucleoside inhibitor α-anilinophenylacetamide (α-APA) R 95845 has been determined at 2.8 å resolution. The inhibitor binds in a hydrophobic pocket near the polymerase active site. The pocket contains five aromatic amino acid residues and the interactions of the side chains of these residues with the aromatic rings of non-nucleoside inhibitors appear to be important for inhibitor binding. Most of the amino acid residues where mutations have been correlated with high levels of resistance to non-nucleoside inhibitors of HIV-1 RT are located close to α-APA. The overall fold of HIV-1 RT in complex with α-APA is similar to that found when in complex with nevirapine, another non-nucleoside inhibitor, but there are significant conformational changes relative to an HIV-1 RT/DNA/Fab complex.Conclusion The non-nucleoside inhibitor-binding pocket has a flexible structure whose mobility may be required for effective polymerization, and may be part of a hinge that permits relative movements of two subdomains of the p66 subunit denoted the ‘palm’ and ‘thumb’. An understanding of the structure of the inhibitor-binding pocket, of the interactions between HIV-1 RT and α-APA, and of the locations of mutations that confer resistance to inhibitors provides a basis for structure-based design of chemotherapeutic agents for the treatment of AIDS

Alterations in voltage-sensing of the mitochondrial permeability transition pore in ANT1-deficient cells

The probability of mitochondrial permeability transition (mPT) pore opening is inversely related to the magnitude of the proton electrochemical gradient. The module conferring sensitivity of the pore to this gradient has not been identified. We investigated mPT's voltage-sensing properties elicited by calcimycin or H2O2 in human fibroblasts exhibiting partial or complete lack of ANT1 and in C2C12 myotubes with knocked-down ANT1 expression. mPT onset was assessed by measuring in situ mitochondrial volume using the 'thinness ratio' and the 'cobalt-calcein' technique. De-energization hastened calcimycin-induced swelling in control and partially-expressing ANT1 fibroblasts, but not in cells lacking ANT1, despite greater losses of mitochondrial membrane potential. Matrix Ca(2+) levels measured by X-rhod-1 or mitochondrially-targeted ratiometric biosensor 4mtD3cpv, or ADP-ATP exchange rates did not differ among cell types. ANT1-null fibroblasts were also resistant to H2O2-induced mitochondrial swelling. Permeabilized C2C12 myotubes with knocked-down ANT1 exhibited higher calcium uptake capacity and voltage-thresholds of mPT opening inferred from cytochrome c release, but intact cells showed no differences in calcimycin-induced onset of mPT, irrespective of energization and ANT1 expression, albeit the number of cells undergoing mPT increased less significantly upon chemically-induced hypoxia than control cells. We conclude that ANT1 confers sensitivity of the pore to the electrochemical gradient

Alterations in voltage-sensing of the mitochondrial permeability transition pore in ANT1-deficient cells

The probability of mitochondrial permeability transition (mPT) pore opening is inversely related to the magnitude of the proton electrochemical gradient. The module conferring sensitivity of the pore to this gradient has not been identified. We investigated mPT's voltage-sensing properties elicited by calcimycin or H2O2 in human fibroblasts exhibiting partial or complete lack of ANT1 and in C2C12 myotubes with knocked-down ANT1 expression. mPT onset was assessed by measuring in situ mitochondrial volume using the 'thinness ratio' and the 'cobalt-calcein' technique. De-energization hastened calcimycin-induced swelling in control and partially-expressing ANT1 fibroblasts, but not in cells lacking ANT1, despite greater losses of mitochondrial membrane potential. Matrix Ca(2+) levels measured by X-rhod-1 or mitochondrially-targeted ratiometric biosensor 4mtD3cpv, or ADP-ATP exchange rates did not differ among cell types. ANT1-null fibroblasts were also resistant to H2O2-induced mitochondrial swelling. Permeabilized C2C12 myotubes with knocked-down ANT1 exhibited higher calcium uptake capacity and voltage-thresholds of mPT opening inferred from cytochrome c release, but intact cells showed no differences in calcimycin-induced onset of mPT, irrespective of energization and ANT1 expression, albeit the number of cells undergoing mPT increased less significantly upon chemically-induced hypoxia than control cells. We conclude that ANT1 confers sensitivity of the pore to the electrochemical gradient

Negative-ion resonances in zinc: A study in elastic electron scattering and electron transmission

The energies, widths, and angular behavior of negative-ion resonances in zinc atoms are determined using the complementary experimental techniques of electron transmission and angular differential elastic scattering