Studies of viomycin, an anti-tuberculosis antibiotic: Copper(II) coordination, DNA degradation and the impact on delta ribozyme cleavage activity

Viomycin is a basic peptide antibiotic, which is among the most effective agents against multidrug-resistant tuberculosis. In this paper we provide the characteristics of its acid base properties, coordination preferences towards the Cu(II) ions, as well as the reactivity of the resulting complexes against plasmid DNA and HDV ribozyme. Careful coordination studies throughout the wide pH range allow for the characterisation of all the Cu(II)-viomycin complex species. The assignment of proton chemical shifts was achieved by NMR experiments, while the DTF level of theory was applied to support molecular structures of the studied complexes. The experiments with the plasmid DNA reveal that at the physiological levels of hydrogen peroxide the Cu(II)-viomycin complex is more aggressive against DNA than uncomplexed metal ions. Moreover, the degradation of DNA by viomycin can be carried out without the presence of transition metal ions. In the studies of antigenomic delta ribozyme catalytic activity, viomycin and its complex are shown to modulate the ribozyme functioning. The molecular modelling approach allows the indication of two different locations of viomycin binding sites to the ribozyme

E2 transition probabilities for decays of isomers observed in neutron-rich odd Sn isotopes

High-spin states were investigated with gamma coincidence techniques in neutron-rich Sn isotopes produced in fission processes following 48Ca + 208Pb, 48Ca + 238U, and 64Ni + 238U reactions. By exploiting delayedand cross-coincidence techniques, level schemes have been delineated in odd 119-125Sn isotopes. Particular attention was paid to the occurrence of 19/2+ and 23/2+ isomeric states for which the available information has now been significantly extended. Reduced transition probabilities, B(E2), extracted from the measured half-lives and the established details of the isomeric decays exhibit a striking regularity. This behavior was compared with the previously observed regularity of the B(E2) amplitudes for the seniority ν = 2 and 3, 10+ and 27/2- isomers in even- and odd-Sn isotopes, respectively

High-seniority excitations in even neutron-rich sn isotopes populated in fusion-fission reactions

High-seniority excitations above the 10+ and 27=2-isomeric states were investigated with gamma coincidence techniques in neutron-rich Sn isotopes produced in fission processes following 48Ca+208Pb, 48Ca+238U and 64Ni+238U reactions. In the data analysis, the delayed gamma coincidence technique was used to establish high-spin state structures in all Sn isotopes with isomeric half-lives below 10 sec. For cases with long-lived isomeric states, the gamma cross-coincidence method was employed to identify such structures. The relevant features of the fusion-fission process were investigated to enable these identifications. The discussion of some details of these analyses is followed by two examples of the results obtained: the 124Sn level scheme and the level energy systematics for selected states established in even Sn isotopes

High-spin shell model states in neutron-rich Sn isotopes

High-spin states with the seniority v ≥ 2 have been investigated in the neutron-rich 118,120,122,124,126Sn isotopes. They were produced in fusion-fission processes following 48Ca + 208Pb, 48Ca + 238U reactions and via fission of target nuclei in the 64Ni + 238U system. By employing techniques of delayed- and cross-coincidences, it was possible to establish level schemes up to an 8 MeV excitation energy. The 13- and 15- states were identified as being isomeric and their half-lives were determined. The reduced transition probabilities extracted for isomeric transitions behave very regularly with the mass number A. The spin-parity values assigned to or suggested for the identified states were supported by shell-model calculations and by systematics

Levels above the 19/2- isomer in Cu71: Persistence of the N=40 neutron shell gap

Two prompt γ rays of energies 2020 and 554 keV were observed in coincidence with delayed transitions depopulating the 19/2- isomer in the Z=29, N=42 Cu71 nucleus. The newly identified transitions are proposed to deexcite the 4776- and 5330-keV levels above the 19/2- isomer. Based on the comparison with the low-lying positive-parity states observed in the Z=42, N=50 Mo92 nucleus, spin and parity 23/2- are proposed for the 4776-keV level in Cu71. The high-energy, 2020-keV transition is interpreted as arising from the breaking of the N=40 neutron core. Shell-model calculations with a Ni56 core reproduce the (23/2-)→(19/2-) gap well, suggesting that the 23/2- state is dominated by πp3/2ν((fp)10(g9/2)4) configurations. The present result constitutes further evidence supporting the view that the N=40 subshell closure persists in Cu71, herewith challenging recent suggestions that the coupling of two or more proton or neutron quasiparticles induces a large polarization of the Ni68 core

Higher-seniority excitations in even neutron-rich Sn isotopes

Excited states above the seniority ν=2 isomers have been investigated in even neutron-rich 118-128Sn isotopes produced by fusion-fission of 6.9 MeV/A Ca48 beams with Pb208 and U238 targets and by fission of 6.7 MeV/A Ni64 beams on a U238 target. Level schemes up to excitation energies in excess of 8 MeV have been established based on multifold γ-ray coincidence relationships measured with the Gammasphere array. Isotopic identification of crucial transitions was achieved through a number of techniques, including prompt and delayed cross-coincidence methods. As a result, seniority ν=4, 15-, and 13- isomers were observed and their half-lives determined. These long-lived states in turn served as steppingstones to delineate the isomeric decays and to locate higher-lying states with good sensitivity. As the observed isomeric decays feed down to 10+ and 7- isomers, firm spin-parity assignments could be proposed for most of the seniority ν=4 states. Higher-lying, seniority ν=6 levels were assigned tentatively on the basis of the observed deexcitation paths as well as of general yrast population arguments. Shell-model calculations were carried out down to Sn122 in the g7/2, d5/2, d3/2, s1/2, and h11/2 model space of neutron holes with respect to a Sn132 core. Effective two-body interactions were adjusted such that satisfactory agreement with data was achieved for Sn130. The results reproduce the experimental level energies and spin-parity assignments rather well. The intrinsic structure of the states is discussed on the basis of the calculated wave functions which, in many instances, point to complex configurations. In a few cases, the proposed assignments lead to unresolved issues. The smooth, systematic decrease of the level energies with mass A is accompanied by the similarly regular behavior with A of the reduced transition probabilities extracted from the isomeric half-lives. This A dependence is discussed for the E1 and E2 transitions in the decay of the seniority ν=4 isomers and is compared to that determined in earlier work for the E2 transition rates from the ν=2,3 isomers

Characterization of the Trans Watson-Crick GU Base Pair Located in the Catalytic Core of the Antigenomic HDV Ribozyme

The HDV ribozyme’s folding pathway is, by far, the most complex folding pathway elucidated to date for a small ribozyme. It includes 6 different steps that have been shown to occur before the chemical cleavage. It is likely that other steps remain to be discovered. One of the most critical of these unknown steps is the formation of the trans Watson-Crick GU base pair within loop III. The U23 and G28 nucleotides that form this base pair are perfectly conserved in all natural variants of the HDV ribozyme, and therefore are considered as being part of the signature of HDV-like ribozymes. Both the formation and the transformation of this base pair have been studied mainly by crystal structure and by molecular dynamic simulations. In order to obtain physical support for the formation of this base pair in solution, a set of experiments, including direct mutagenesis, the site-specific substitution of chemical groups, kinetic studies, chemical probing and magnesium-induced cleavage, were performed with the specific goal of characterizing this trans Watson-Crick GU base pair in an antigenomic HDV ribozyme. Both U23 and G28 can be substituted for nucleotides that likely preserve some of the H-bond interactions present before and after the cleavage step. The formation of the more stable trans Watson-Crick base pair is shown to be a post-cleavage event, while a possibly weaker trans Watson-Crick/Hoogsteen interaction seems to form before the cleavage step. The formation of this unusually stable post-cleavage base pair may act as a driving force on the chemical cleavage by favouring the formation of a more stable ground state of the product-ribozyme complex. To our knowledge, this represents the first demonstration of a potential stabilising role of a post-cleavage conformational switch event in a ribozyme-catalyzed reaction

Targeted calcium influx boosts cytotoxic T lymphocyte function in the tumour microenvironment

Adoptive cell transfer utilizing tumour-targeting cytotoxic T lymphocytes (CTLs) is one of the most effective immunotherapies against haematological malignancies, but significant clinical success has not yet been achieved in solid tumours due in part to the strong immunosuppressive tumour microenvironment. Here, we show that suppression of CTL killing by CD4+CD25+Foxp+ regulatory T cell (Treg) is in part mediated by TGFβ-induced inhibition of inositol trisphosphate (IP3) production, leading to a decrease in T cell receptor (TCR)-dependent intracellular Ca2+ response. Highly selective optical control of Ca2+ signalling in adoptively transferred CTLs enhances T cell activation and IFN-γ production in vitro, leading to a significant reduction in tumour growth in mice. Altogether, our findings indicate that the targeted optogenetic stimulation of intracellular Ca2+ signal allows for the remote control of cytotoxic effector functions of adoptively transferred T cells with outstanding spatial resolution by boosting T cell immune responses at the tumour sites

Doubly magic Pb 208: High-spin states, isomers, and E3 collectivity in the yrast decay

Yrast and near-yrast levels up to spin values in excess of I=30 have been delineated in the doubly magic Pb208 nucleus following deep-inelastic reactions involving Pb208 targets and, mostly, 430-MeV Ca48 and 1440-MeV Pb208 beams. The level scheme was established up to an excitation energy of 16.4 MeV, based on multifold γ-ray coincidence relationships measured with the Gammasphere array. Below the well-known, 0.5-μs 10+ isomer, ten new transitions were added to earlier work. The delineation of the higher parts of the level sequence benefited from analyses involving a number of prompt- and delayed-coincidence conditions. Three new isomeric states were established along the yrast line with Iπ=20- (10 342 keV), 23+ (11 361 keV), and 28- (13 675 keV), and respective half-lives of 22(3), 12.7(2), and 60(6) ns. Gamma transitions were also identified preceding in time the 28- isomer; however, only a few could be placed in the level scheme and no firm spin-parity quantum numbers could be proposed. In contrast, for most states below this 28- isomer, firm spin-parity values were assigned, based on total electron-conversion coefficients, deduced for low-energy (<500keV) transitions from γ-intensity balances, and on measured γ-ray angular distributions. The latter also enabled the quantitative determination of mixing ratios. The transition probabilities extracted for all isomeric transitions in Pb208 have been reviewed and discussed in terms of the intrinsic structure of the initial and final levels involved. Particular emphasis was placed on the many observed E3 transitions as they often exhibit significant enhancements in strength [of the order of tens of Weisskopf units (W.u.)] comparable to the one seen for the neutron j15/2→g9/2 E3 transition in Pb209. In this context, the enhancement of the 725-keV E3 transition (56 W.u.) associated with the decay of the highest-lying 28- isomer observed in this work remains particularly challenging to explain. Large-scale shell-model calculations were performed with two approaches, a first one where the 1, 2, and 3 particle-hole excitations do not mix with one another, and another more complex one, in which such mixing takes place. The calculated levels were compared with the data and a general agreement is observed for most of the Pb208 level scheme. At the highest spins and energies, however, the correspondence between theory and experiment is less satisfactory and the experimental yrast line appears to be more regular than the calculated one. This regularity is notable when the level energies are plotted versus the I(I+1) product and the observed, nearly linear, behavior was considered within a simple "rotational" interpretation. Within this approximate picture, the extracted moment of inertia suggests that only the 76 valence nucleons participate in the "rotation" and that the Sn132 spherical core remains inert

Identification of the g9/2-proton bands in the neutron-rich Ga71,73,75,77 nuclei

Excited states in the odd-AGa71,73,75,77 nuclei have been populated in deep-inelastic reactions of a Ge76 beam at 530 MeV with a thick U238 target. High-spin sequences built upon the 9/2+, 5/2-, and 3/2- states were identified in all four isotopes. A comparison of the observed structures with the yrast positive-parity states in the neighboring even-even Zn cores indicates that the newly identified levels may be regarded as arising from the relatively weak coupling of the odd proton to the core states. However, significant contributions from broken pairs are expected to be present in this region of excitation energy. The present data set also provides clarification of previously reported decay paths of the low-energy levels in Ga71,73,75,77