Some remarks on two-periodic modules over local rings

In this note, some properties of finitely generated two-periodic modules over commutative Noetherian local rings have been studied. We prove a weaker version of the Huneke-Wiegand conjecture for two-periodic modules -- under certain assumptions, a two-periodic module is necessarily free. Given a two-periodic module with finite rank over a one-dimensional local ring, it is shown that the tensor product of the module with its dual has non-zero torsion. Moreover, if the base ring is one-dimensional, we show that with certain assumptions on modules, the tensor product of a two-periodic module with another finitely generated module is torsion-free if and only if the pair of modules is Tor-independent. We also discuss Auslander's depth formula for a Tor-independent pair of modules in this setup. It is proved that such a formula holds for a Tor-independent pair of modules if one of the modules is two-periodic with finite Gorenstein dimension.Comment: 11 pages. Comments are welcom

Topology of moduli of parabolic connections with fixed determinant

Let $X$ be a compact Riemann surface of genus $g \geq 2$ and $D\subset X$ be a fixed finite subset. Let $\xi$ be a line bundle of degree $d$ over $X$. Let $\mathcal{M}(\alpha, r, \xi)$ (respectively, $\mathcal{M}_{\mathrm{conn}}(\alpha, r, \xi)$) denote the moduli space of stable parabolic bundles (respectively, parabolic connections) of rank $r$ $(\geq 2)$, determinant $\xi$ and full flag generic rational parabolic weight type $\alpha$. We show that $\pi_k(\mathcal{M}_{\mathrm{conn}}(\alpha, r, \xi)) \cong \pi_k(\mathcal{M}(\alpha, r, \xi))$ for $k \leq2(r-1)(g-1)-1$. As a consequence, we deduce that the moduli space $\mathcal{M}_{\mathrm{conn}}(\alpha, r, \xi)$ is simply connected. We also show that the Hodge structures on the torsion-free parts of both the cohomologies $H^k(\mathcal{M}_{\mathrm{conn}}(\alpha, r, \xi),\mathbb{Z})$ and $H^k(\mathcal{M}(\alpha, r, \xi),\mathbb{Z})$ are isomorphic for all $k\leq 2(r-1)(g-1)+1$.Comment: 12 page

Differential induction of Leishmania donovani bi-subunit topoisomerase I–DNA cleavage complex by selected flavones and camptothecin: activity of flavones against camptothecin-resistant topoisomerase I

Emergence of the bi-subunit topoisomerase I in the kinetoplastid family (Trypanosoma and Leishmania) has brought a new twist in topoisomerase research related to evolution, functional conservation and preferential sensitivities to the specific inhibitors of type IB topoisomerase family. In the present study, we describe that naturally occurring flavones baicalein, luteolin and quercetin are potent inhibitors of the recombinant Leishmania donovani topoisomerase I. These compounds bind to the free enzyme and also intercalate into the DNA at a very high concentration (300 µM) without binding to the minor grove. Here, we show that inhibition of topoisomerase I by these flavones is due to stabilization of topoisomerase I–DNA cleavage complexes, which subsequently inhibit the religation step. Their ability to stabilize the covalent topoisomerase I–DNA complex in vitro and in living cells is similar to that of the known topoisomerase I inhibitor camptothecin (CPT). However, in contrast to CPT, baicalein and luteolin failed to inhibit the religation step when the drugs were added to pre-formed enzyme substrate binary complex. This differential mechanism to induce the stabilization of cleavable complex with topoisomerase I and DNA by these selected flavones and CPT led us to investigate the effect of baicalein and luteolin on CPT-resistant mutant enzyme LdTOP1Δ39LS lacking 1–39 amino acids of the large subunit [B. B. Das, N. Sen, S. B. Dasgupta, A. Ganguly and H. K. Majumder (2005) J. Biol. Chem. 280, 16335–16344]. Baicalein and luteolin stabilize duplex oligonucleotide cleavage with LdTOP1Δ39LS. This observation was further supported by the stabilization of in vivo cleavable complex by baicalein and luteolin with highly CPT-resistant L.donovani strain. Taken together, our data suggest that the interacting amino acid residues of topoisomerase I may be partially overlapping or different for flavones and CPT. This study illuminates new properties of the flavones and provide additional insights into the ligand binding properties of L.donovani topoisomerase I

‘LeishMan’ topoisomerase I: an ideal chimera for unraveling the role of the small subunit of unusual bi-subunit topoisomerase I from Leishmania donovani

The active site tyrosine residue of all monomeric type IB topoisomerases resides in the C-terminal domain of the enzyme. Leishmania donovani, possesses unusual heterodimeric type IB topoisomerase. The small subunit harbors the catalytic tyrosine within the SKXXY motif. To explore the functional relationship between the two subunits, we have replaced the small subunit of L.donovani topoisomerase I with a C-terminal fragment of human topoisomerase I (HTOP14). The purified LdTOP1L (large subunit of L.donovani topoisomerase I) and HTOP14 were able to reconstitute topoisomerase I activity when mixed in vitro. This unusual enzyme, ‘LeishMan’ topoisomerase I (Leish for Leishmania and Man for human) exhibits less efficiency in DNA binding and strand passage compared with LdTOP1L/S. Fusion of LdTOP1L with HTOP14 yielded a more efficient enzyme with greater affinity for DNA and faster strand passage ability. Both the chimeric enzymes are less sensitive to camptothecin than LdTOP1L/S. Restoration of topoisomerase I activity by LdTOP1L and HTOP14 suggests that the small subunit of L.donovani topoisomerase I is primarily required for supplying the catalytic tyrosine. Moreover, changes in the enzyme properties due to substitution of LdTOP1S with HTOP14 indicate that the small subunit contributes to subunit interaction and catalytic efficiency of the enzyme

Leishmania Donovani: Dyskinetoplastid Cells Survive and Proliferate in the Presence of Pyruvate and Uridine but do not Undergo Apoptosis after Treatment with Camptothecin.

We have shown that treatment with luteolin in leishmanial cells causes loss of mt-DNA and induces apoptosis through mitochondria dependent pathway [Sen, N., Das, B.B., Ganguly, A., Banerjee, B., Sen, T., Majumder, H.K., 2006. Leishmania donovani: intracellular ATP level regulates apoptosis-like death in luteolin induced dyskinetoplastid cells. Experimental Parasitology, in press]. Here, we report that mitochondrial DNA depleted leishmanial cells require exogenous sources of pyruvate and uridine to survive and proliferate. The presence of pyruvate and uridine in a growing media help them to produce suYcient amount of glycolytic ATP to maintain the mitochondrial membrane potential in the absence of their functional ETC. Treatment of wild type cells with CPT causes generation of ROS that leads to apoptosis. But unlike the normal cells ROS was not generated in these mt-DNA depleted cells after treatment with CPT. Taken together we have shown for the Wrst time that dyskinetoplastid cells are auxotrophic for pyruvate and uridine and apoptosis cannot be induced in these cells in the presence of CPT. Therefore, the presence of mitochondrial DNA is absolutely necessary for the cytotoxicity of CPT in kinetoplastid parasites

Leishmania donovani: Intracellular ATP level regulates apoptosis-like death in luteolin induced dyskinetoplastid cells

Leishmaniasis presents a spectrum of diseases ranging from benign cutaneous lesions to the often-fatal visceralizing form. Luteolin, a dietary flavone induces apoptosis-like death in both promastigote and amastigote forms of Leishmania, the causative agent of the diseases. Here, we have elucidated the mechanism of action of luteolin by analyzing the mitochondrial and cytosolic changes associated with apoptosis-like death of leishmanial cells. In Leishmania donovani, treatment with luteolin induces the loss of both maxicircles and minicircles which resulted in the formation of dyskinetoplastid cells. The loss of mitochondrial DNA causes reduction in the activities of complex I, II, III, and IV of electron transport chain. However, the mitochondrial ATPase activity of complex V remains almost unaltered during treatment with luteolin but the sensitivity to oligomycin is lost. The inactivation of ETC complex is associated with decrease in mitochondrial as well as glycolytic ATP production, which is responsible for depolarization of ΔΨ<SUB>m</SUB> and alteration in mitochondrial structure. This event is followed by the release of cytochrome c from mitochondria in mt-DNA depleted leishmanial cells and causes an activation of caspase like proteases. Collectively our results provide the first insight into the mechanistic pathway of apoptosis-like death where inhibition of glycolytic ATP production is an essential event responsible for depolarization of ΔΨ<SUB>m</SUB> in mt-DNA depleted cells to propagate apoptosis-like death in leishmanial cells

Betulinic Acid, a Catalytic Inhibitor of Topoisomerase I, Inhibits Reactive Oxygen Species–Mediated Apoptotic Topoisomerase I–DNA Cleavable Complex Formation in Prostate Cancer Cells but Does Not Affect the Process of Cell Death

The ubiquitious enzyme topoisomerase I can be targeted by drugs which turn these enzymes into cellular poisons and subsequently induce cell death. Drugs like staurosporine, which do not target topoisomerase I directly, can also lead to stabilization of topoisomerase I–DNAcleavable complexes by an indirect process of reactive oxygen species (ROS) generation and subsequent oxidative DNAdamage. In this study, we show that betulinic acid, a catalytic inhibitor of topoisomerases, inhibits the formation of apoptotic topoisomerase I–DNAclea vable complexes in prostate cancer cells induced by drugs like camptothecin, staurosporine, and etoposide. Although events like ROS generation, oxidative DNA damage, and DNAfragmentation were observed after betulinic acid treatment, there is no topoisomerase I–DNAclea vable complex formation, which is a key step in ROS-induced apoptotic processes. We have shown that betulinic acid interacts with cellular topoisomerase I and prohibits its interaction with the oxidatively damaged DNA. Using oligonucleotide containing 8-oxoguanosine modification, we have shown that betulinic acid inhibits its cleavage by topoisomerase I in vitro. Whereas silencing of topoisomerase I gene by small interfering RNAreduces cell death in the case of staurosporine and camptothecin, it cannot substantially reduce betulinic acid– induced cell death. Thus, our study provides evidence that betulinic acid inhibits formation of apoptotic topoisomerase I–DNAcomplexes and prevents the cellular topoisomerase I from directly participating in the apoptotic proces

Analysis of drug induced covalent topoisomerase I–DNA complex formation in promastigotes by KCl-SDS precipitation assay

<p><b>Copyright information:</b></p><p>Taken from "Differential induction of bi-subunit topoisomerase I–DNA cleavage complex by selected flavones and camptothecin: activity of flavones against camptothecin-resistant topoisomerase I"</p><p>Nucleic Acids Research 2006;34(4):1121-1132.</p><p>Published online 18 Feb 2006</p><p>PMCID:PMC1373691.</p><p>© The Author 2006. Published by Oxford University Press. All rights reserved</p> Exponentially growing promastigotes (5 × 10 cells/ml) were labeled with [H]thymidine at 22°C for 24 h and then treated with different concentrations of drugs as indicated. Parts of the labeled cells were treated with DHBA (150 µM) for 10 min before the addition of different concentration of baicalein as indicated. SDS-K precipitable complex were measured as described in Materials and Methods. Experiments were performed three times and representative data from one set of experiments are expressed as means ± SD. Variations among different set of experiments wer

Not Available

The article Received 11 August 2016 Revised 11 September 2016 Accepted 16 September 2016 PublishYak is an iconic symbol of Tibet and high altitudes of Northeast India. It is highly cherished for milk, meat, and skin. However, yaks suffer drastic change in milk production, weight loss, etc, when infested by parasites. Among them, infestation by leeches is a serious problem in the Himalayan belt of Northeast India. The parasite feeds on blood externally or from body orifices, like nasopharynx, oral, rectum, etc. But there has been limited data about the leech species infesting the yak in that region because of the difficulties in morphological identification due to plasticity of the body, changes in shape, and surface structure and thus, warrants for the molecular characterization of leech. In anticipation, this study would be influential in proper identification of leech species infesting yak track and also helpful in inventorying of leech species in Northeast India. Here, we investigated, through combined approach of molecular markers and morphological parameters for the identification of leech species infesting yak. The DNA sequences of COI barcode fragment, 18S and 28S rDNA, were analyzed for species identification. The generated sequences were subjected to similarity match in global database and analyzed further through Neighbour-Joining, K2P distance based as well as ML approach. Among the three markers, only COI was successful in delineating species whereas the 18S and 28S failed to delineate the species. Our study confirmed the presence of the species from genus Hirudinaria, Haemadipsa, Whitmania, and one species Myxobdella annandalae, which has not been previously reported from this region.Department of Biotechnology, Government of Indi