Structural characterisation of transcription and replication through cisplatin lesioned DNA

Replication of the genome is strongly inhibited when high fidelity DNA polymerases encounter unrepaired DNA lesions, which can not be processed. The highly stringent active sites of these polymerases are unable to accommodate damaged bases and therefore DNA lesions block the replication fork progression. In order to overcome this problem, cells have evolved mechanisms for either repairing the damage, or synthesising past it with specially adapted polymerasases. Eukaryotic DNA polymerase eta (Pol eta), belonging to the Y-family of DNA polymerases, is outstanding in its ability to replicate through a variety of highly distorting DNA lesions such as cyclobutane pyrimidine dimers (CPDs), which are the main UV-induced lesions. Also cisplatin induced 1,2-d(GpG) adducts (Pt-GGs), which are formed in a typical cancer therapy with cisplatin can be processed by Pol eta. The bypass of such intrastrand crosslinks by high fidelity DNA polymerases is particularly difficult because two adjacent coding bases are simultaneously damaged. Thus, replication by Pol eta allows organisms to survive exposure to sunlight or, in the case of cisplatin, gives rise to resistances against cisplatin treatment. Mutations in the human POLH gene, encoding Pol eta, causes the variant form of xeroderma pigmentosum (XP V), characterized by the failure to copy through CPDs. This leads to strongly increased UV sensitivity and skin cancer predisposition. This thesis describes mechanistic investigations of the translesion synthesis (TLS) process by S. cerevisiae DNA Pol eta at atomic resolution, which were undertaken in collaboration with the Hopfner group. To study this process, cisplatin lesioned DNA had to be prepared first. Once this technique was established, the catalytic fragment of Pol eta was crystallized as ternary complex with incoming 2',3'-dideoxycytidine 5'-triphosphate (ddCTP) and an primer - template DNA containing a site specific Pt-GG adduct. The first obtained structure shows the ddCTP positioned in a loosely bound conformation in the active site, hydrogen bonded to the templating base. Realizing the importance of the 3’ hydroxy group for positioning the NTP and the DNA correctly inside the polymerase, the complex was crystallized again with a 2’-deoxynucleoside 5’-triphosphate (dNTP). To prevent nucleotidyl transfer, primer strands which terminate at the 3’-end with a 2’,3’ dideoxy ribose were prepared by reverse DNA synthesis and used for cocrystallization. The resulting crystals diffracted typically to 3.1-3.3Å resolution at a synchrotron light source. A Pol eta specific arginine (Arg73 in yeast Pol eta) was identified for its importance to position the dNTP correctly in the active site and was shown to be necessary for lesion bypass. In contrast to the fixed preorientation of the dNTP in the active site, the damaged DNA is bound flexibly in a rather open DNA binding cleft. Nucleotidyl transfer requires a revolving of the DNA, energetically driven by hydrogen bonding of the templating base to the dNTP. For the 3’dG of the Pt-GG, this step is accomplished by bona fide Watson-Crick base pairs to dCTP and is biochemically efficient and accurate. In contrast, bypass of the 5’dG of the Pt-GG is less efficient and promiscuous for dCTP and dATP. Structurally, this can be attributed to misalignment of the templating 5’dG due to the rigid Pt crosslink. In cooperation with the Cramer group the structural reasons for the blockage of RNA Polymerase II (RNAP II) by the cisplatin lesion were elucidated. Using structural as well as biochemical methods it could be shown that stalling results from a translocation barrier that prevents delivery of the lesion to the active site. AMP misincorporation occurs at the barrier and also at an abasic site, suggesting that it arises from nontemplated synthesis according to an 'A-rule' known for DNA polymerases. RNAP II can bypass a cisplatin lesion that is artificially placed beyond the translocation barrier, even in the presence of a G A mismatch. Thus, the barrier prevents transcriptional mutagenesis

Three-body analysis of incoherent η\eta-photoproduction on the deuteron in the near threshold region

A three-body calculation of the reaction $\gamma d\to\eta np$ in the energy region from threshold up to 30 MeV above has been performed. The primary goal of this study is to assess the importance of the three-body aspects in the hadronic sector of this reaction. Results are presented for the $\eta$-meson spectrum as well as for the total cross section. The three-body results differ significantly from those predicted by a simple rescattering model in which only first-order $\eta N$- and $NN$-interactions in the final state are considered. The major features of the experimental data are well reproduced although right at threshold the rather large total cross section could not be explained.Comment: 6 pages revtex including 3 figure

Chromatin association of the SMC5/6 complex is dependent on binding of its NSE3 subunit to DNA

SMC5/6 is a highly conserved protein complex related to cohesin and condensin, which are the key components of higher-order chromatin structures. The SMC5/6 complex is essential for proliferation in yeast and is involved in replication fork stability and processing. However, the precise mechanism of action of SMC5/6 is not known. Here we present evidence that the NSE1/NSE3/NSE4 sub-complex of SMC5/6 binds to double-stranded DNA without any preference for DNA-replication/recombination intermediates. Mutations of key basic residues within the NSE1/NSE3/NSE4 DNA-binding surface reduce binding to DNA in vitro. Their introduction into the Schizosaccharomyces pombe genome results in cell death or hypersensitivity to DNA damaging agents. Chromatin immunoprecipitation analysis of the hypomorphic nse3 DNA-binding mutant shows a reduced association of fission yeast SMC5/6 with chromatin. Based on our results, we propose a model for loading of the SMC5/6 complex onto the chromatin

Dynamical coupled-channel model of meson production reactions in the nucleon resonance region

A dynamical coupled-channel model is presented for investigating the nucleon resonances in the meson production reactions induced by pions and photons. The model is based on an energy-independent Hamiltonian which is derived from a set of Lagrangians by using a unitary transformation method. By applying the projection operator techniques,we derive a set of coupled-channel equations which satisfy the unitarity conditions within the channel space spanned by the considered two-particle meson-baryon states and the three-particle $\pi\pi N$ state. We present and explain in detail a numerical method based on a spline-function expansion for solving the resulting coupled-channel equations which contain logarithmically divergent one-particle-exchange driving terms resulted from the $\pi\pi N$ unitarity cut. We show that this driving term can generate rapidly varying structure in the reaction amplitudes associated with the unstable particle channels. It also has large effects in determining the two-pion production cross sections. Our results indicate that cautions must be taken to interpret the $N^*$ parameters extracted from using models which do not include $\pi\pi N$ cut effects.Comment: 73 pages, 20 figure

Ξ−d→nΛΛ\Xi^{-} d\to n\Lambda\Lambda and the ΛΛ\Lambda\Lambda final state interaction

The reaction $\Xi^-d\to n\Lambda\Lambda$ is studied within the framework of the Faddeev equations as a possible tool to gain insight into the final state $\Lambda$--$\Lambda$ interaction. The neutron differential energy spectrum gives a final state interaction that is sensitive to both the $\Lambda$--$\Lambda$ amplitude at threshold, and the coupling between the $\Lambda$--$\Lambda$ and $\Xi$--$N$ channels. The latter is a result of interference between two mechanisms for the production of the final state, which suggests that this reaction could give a measure of flavor SU(3) violation in the two-baryon system.Comment: 24 pages, 8 figures, submitted to Physical Reviw

Few Body Reserch - Summary

Few-body research history, achievements, current development and challenges are presented.Comment: 21 pages, 2 tables, Summary talk at 18th International IUPAP Conference on Few-Body Problems in Physics August 21-26. 2006 Santos SP Brazil; to be published in Nuclear Physic

Destabilized SMC5/6 complex leads to chromosome breakage syndrome with severe lung disease

The structural maintenance of chromosomes (SMC) family of proteins supports mitotic proliferation, meiosis, and DNA repair to control genomic stability. Impairments in chromosome maintenance are linked to rare chromosome breakage disorders. Here, we have identified a chromosome breakage syndrome associated with severe lung disease in early childhood. Four children from two unrelated kindreds died of severe pulmonary disease during infancy following viral pneumonia with evidence of combined T and B cell immunodeficiency. Whole exome sequencing revealed biallelic missense mutations in the NSMCE3 (also known as NDNL2) gene, which encodes a subunit of the SMC5/6 complex that is essential for DNA damage response and chromosome segregation. The NSMCE3 mutations disrupted interactions within the SMC5/6 complex, leading to destabilization of the complex. Patient cells showed chromosome rearrangements, micronuclei, sensitivity to replication stress and DNA damage, and defective homologous recombination. This work associates missense mutations in NSMCE3 with an autosomal recessive chromosome breakage syndrome that leads to defective T and B cell function and acute respiratory distress syndrome in early childhood

Survival benefit with checkpoint inhibitors versus chemotherapy is modified by brain metastases in patients with recurrent small cell lung cancer

IntroductionSmall cell lung cancer (SCLC) is a rapidly growing malignancy with early distant metastases. Up to 70% will develop brain metastases, and the poor prognosis of these patients has not changed considerably. The potential of checkpoint inhibitors (CPI) in treating recurrent (r/r) SCLC and their effect on brain metastases remain unclear.MethodsIn this retrospective multicenter study, we analyzed r/r SCLC patients receiving second or further-line CPI versus chemotherapy between 2010 and 2020. We applied multivariable-adjusted Cox regression analysis to test for differences in 1-year mortality and real-world progression. We then used interaction analysis to evaluate whether brain metastases (BM) and/or cranial radiotherapy (CRT) modified the effect of CPI versus chemotherapy on overall survival.ResultsAmong 285 patients, 99 (35%) received CPI and 186 (65%) patients received chemotherapy. Most patients (93%) in the CPI group received nivolumab/ipilimumab. Chemotherapy patients were entirely CPI-naïve and only one CPI patient had received atezolizumab for first-line treatment. CPI was associated with a lower risk of 1-year mortality (adjusted Hazard Ratio [HRadj] 0.59, 95% CI 0.42 to 0.82, p=0.002). This benefit was modified by BM and CRT, indicating a pronounced effect in patients without BM (with CRT: HRadj 0.34, p=0.003; no CRT: HRadj 0.50, p=0.05), while there was no effect in patients with BM who received CRT (HRadj 0.85, p=0.59).ConclusionCPI was associated with a lower risk of 1-year mortality compared to chemotherapy. However, the effect on OS was significantly modified by intracranial disease and radiotherapy, suggesting the benefit was driven by patients without BM

Structural and Functional Insights into Endoglin Ligand Recognition and Binding

Endoglin, a type I membrane glycoprotein expressed as a disulfide-linked homodimer on human vascular endothelial cells, is a component of the transforming growth factor (TGF)-β receptor complex and is implicated in a dominant vascular dysplasia known as hereditary hemorrhagic telangiectasia as well as in preeclampsia. It interacts with the type I TGF-β signaling receptor activin receptor-like kinase (ALK)1 and modulates cellular responses to Bone Morphogenetic Protein (BMP)-9 and BMP-10. Structurally, besides carrying a zona pellucida (ZP) domain, endoglin contains at its N-terminal extracellular region a domain of unknown function and without homology to any other known protein, therefore called the orphan domain (OD). In this study, we have determined the recognition and binding ability of full length ALK1, endoglin and constructs encompassing the OD to BMP-9 using combined methods, consisting of surface plasmon resonance and cellular assays. ALK1 and endoglin ectodomains bind, independently of their glycosylation state and without cooperativity, to different sites of BMP-9. The OD comprising residues 22 to 337 was identified among the present constructs as the minimal active endoglin domain needed for partner recognition. These studies also pinpointed to Cys350 as being responsible for the dimerization of endoglin. In contrast to the complete endoglin ectodomain, the OD is a monomer and its small angle X-ray scattering characterization revealed a compact conformation in solution into which a de novo model was fitted