156 research outputs found
Captured snapshots of PARP1 in the active state reveal the mechanics of PARP1 allostery
No full textPARP1 rapidly detects DNA strand break damage and allosterically signals break detection to the PARP1 catalytic domain to activate poly(ADP-ribose) production from NAD+. PARP1 activation is characterized by dynamic changes in the structure of a regulatory helical domain (HD); yet, there are limited insights into the specific contributions that the HD makes to PARP1 allostery. Here, we have determined crystal structures of PARP1 in isolated active states that display specific HD conformations. These captured snapshots and biochemical analysis illustrate HD contributions to PARP1 multi-domain and high-affinity interaction with DNA damage, provide novel insights into the mechanics of PARP1 allostery, and indicate how HD active conformations correspond to alterations in the catalytic region that reveal the active site to NAD+. Our work deepens the understanding of PARP1 catalytic activation, the dynamics of the binding site of PARP inhibitor compounds, and the mechanisms regulating PARP1 retention on DNA damage
The shieldin complex mediates 53BP1-dependent DNA repair.
Get PDF53BP1 is a chromatin-binding protein that regulates the repair of DNA double-strand breaks by suppressing the nucleolytic resection of DNA termini. This function of 53BP1 requires interactions with PTIP and RIF1, the latter of which recruits REV7 (also known as MAD2L2) to break sites. How 53BP1-pathway proteins shield DNA ends is currently unknown, but there are two models that provide the best potential explanation of their action. In one model the 53BP1 complex strengthens the nucleosomal barrier to end-resection nucleases, and in the other 53BP1 recruits effector proteins with end-protection activity. Here we identify a 53BP1 effector complex, shieldin, that includes C20orf196 (also known as SHLD1), FAM35A (SHLD2), CTC-534A2.2 (SHLD3) and REV7. Shieldin localizes to double-strand-break sites in a 53BP1- and RIF1-dependent manner, and its SHLD2 subunit binds to single-stranded DNA via OB-fold domains that are analogous to those of RPA1 and POT1. Loss of shieldin impairs non-homologous end-joining, leads to defective immunoglobulin class switching and causes hyper-resection. Mutations in genes that encode shieldin subunits also cause resistance to poly(ADP-ribose) polymerase inhibition in BRCA1-deficient cells and tumours, owing to restoration of homologous recombination. Finally, we show that binding of single-stranded DNA by SHLD2 is critical for shieldin function, consistent with a model in which shieldin protects DNA ends to mediate 53BP1-dependent DNA repair
Some Inequalities for Normal Operators in Hilbert Spaces
No full textSome inequalities for normal operators in Hilbert spaces are given. For this purpose, some results for vectors in inner product spaces due to Buzano, Dunkl-Williams, Hile, Goldstein-Ryff-Clarke, Dragomir-S´andor and the author are employed
Coupling bimolecular PARylation biosensors with genetic screens to identify PARylation targets
Get PDFAbstractPoly (ADP-ribose)ylation is a dynamic protein modification that regulates multiple cellular processes. Here, we describe a system for identifying and characterizing PARylation events that exploits the ability of a PBZ (PAR-binding zinc finger) protein domain to bind PAR with high-affinity. By linking PBZ domains to bimolecular fluorescent complementation biosensors, we developed fluorescent PAR biosensors that allow the detection of temporal and spatial PARylation events in live cells. Exploiting transposon-mediated recombination, we integrate the PAR biosensor en masse into thousands of protein coding genes in living cells. Using these PAR-biosensor “tagged” cells in a genetic screen we carry out a large-scale identification of PARylation targets. This identifies CTIF (CBP80/CBP20-dependent translation initiation factor) as a novel PARylation target of the tankyrase enzymes in the centrosomal region of cells, which plays a role in the distribution of the centrosomal satellites.</jats:p
The Perturbed Median Principle for Integral Inequalities with Applications
Get PDFIn this paper a perturbed version of the Median Principle introduced
by the author in 'The median principle for inequalities and applications' is developed. Applications for various Riemann-
Stieltjes integral and Lebesgue integral inequalities are also provided
Sirtuin inhibition is synthetic lethal with BRCA1 or BRCA2 deficiency
No full textBajrami, Walker et al. investigated the synthetic lethality between BRCA gene defects and inhibition of two sirtuin genes, SIRT1 or SIRT6, which was found to be associated with replication stress and increased PARylation. The authors demonstrated that the SIRT/BRCA1 synthetic lethality was reversed by genetic ablation of PARP1 or HPF1
New Reverse Inequalities for Normal Operators in Hilbert Spaces
No full textIn this paper, more reverse inequalities for the class of normal
operators, are established. Some of the obtained results are based on recent
reverse results for the Schwarz inequality in Hilbert spaces due to the author
Upper Bounds for the Euclidean Operator Radius and Applications
No full textThe main aim of the present paper is to establish various sharp
upper bounds for the Euclidean operator radius of an n−tuple of bounded
linear operators on a Hilbert space. The tools used are provided by several
generalisations of Bessel inequality due to Boas-Bellman, Bombieri and the
author. Natural applications for the norm and the numerical radius of bounded
linear operators on Hilbert spaces are also given
Inequalities for some Functionals Associated with Bounded Linear Operators in Hilbert Spaces
No full textSome inequalities between the operator norm, numerical radius
and functional are established. New upper bounds for the nonnegative
quantity that complement some recent results of the author are given as well
A HUWE1 defect causes PARP inhibitor resistance by modulating the BRCA1-∆11q splice variant
No full textAlthough PARP inhibitors (PARPi) now form part of the standard-of-care for the treatment of homologous recombination defective cancers, de novo and acquired resistance limits their overall effectiveness. Previously, overexpression of the BRCA1-∆11q splice variant has been shown to cause PARPi resistance. How cancer cells achieve increased BRCA1-∆11q expression has remained unclear. Using isogenic cells with different BRCA1 mutations, we show that reduction in HUWE1 leads to increased levels of BRCA1-∆11q and PARPi resistance. This effect is specific to cells able to express BRCA1-∆11q (e.g. BRCA1 exon 11 mutant cells) and is not seen in BRCA1 mutants that cannot express BRCA1-∆11q, nor in BRCA2 mutant cells. As well as increasing levels of BRCA1-∆11q protein in exon 11 mutant cells, HUWE1 silencing also restores RAD51 nuclear foci and platinum salt resistance. HUWE1 catalytic domain mutations were also seen in a case of PARPi resistant, BRCA1 exon 11 mutant, high grade serous ovarian cancer. These results suggest how elevated levels of BRCA1-∆11q and PARPi resistance can be achieved, identify HUWE1 as a candidate biomarker of PARPi resistance for assessment in future clinical trials and illustrate how some PARPi resistance mechanisms may only operate in patients with particular BRCA1 mutations
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