ATXN3 controls DNA replication and transcription by regulating chromatin structure.

The deubiquitinating enzyme Ataxin-3 (ATXN3) contains a polyglutamine (PolyQ) region, the expansion of which causes spinocerebellar ataxia type-3 (SCA3). ATXN3 has multiple functions, such as regulating transcription or controlling genomic stability after DNA damage. Here we report the role of ATXN3 in chromatin organization during unperturbed conditions, in a catalytic-independent manner. The lack of ATXN3 leads to abnormalities in nuclear and nucleolar morphology, alters DNA replication timing and increases transcription. Additionally, indicators of more open chromatin, such as increased mobility of histone H1, changes in epigenetic marks and higher sensitivity to micrococcal nuclease digestion were detected in the absence of ATXN3. Interestingly, the effects observed in cells lacking ATXN3 are epistatic to the inhibition or lack of the histone deacetylase 3 (HDAC3), an interaction partner of ATXN3. The absence of ATXN3 decreases the recruitment of endogenous HDAC3 to the chromatin, as well as the HDAC3 nuclear/cytoplasm ratio after HDAC3 overexpression, suggesting that ATXN3 controls the subcellular localization of HDAC3. Importantly, the overexpression of a PolyQ-expanded version of ATXN3 behaves as a null mutant, altering DNA replication parameters, epigenetic marks and the subcellular distribution of HDAC3, giving new insights into the molecular basis of the disease.

The protease SPRTN and SUMOylation coordinate DNA-protein crosslink repair to prevent genome instability.

DNA-protein crosslinks (DPCs) are a specific type of DNA lesion in which proteins are covalently attached to DNA. Unrepaired DPCs lead to genomic instability, cancer, neurodegeneration, and accelerated aging. DPC proteolysis was recently identified as a specialized pathway for DPC repair. The DNA-dependent protease SPRTN and the 26S proteasome emerged as two independent proteolytic systems. DPCs are also repaired by homologous recombination (HR), a canonical DNA repair pathway. While studying the cellular response to DPC formation, we identify ubiquitylation and SUMOylation as two major signaling events in DNA replication-coupled DPC repair. DPC ubiquitylation recruits SPRTN to repair sites, promoting DPC removal. DPC SUMOylation prevents DNA double-strand break formation, HR activation, and potentially deleterious genomic rearrangements. In this way, SUMOylation channels DPC repair toward SPRTN proteolysis, which is a safer pathway choice for DPC repair and prevention of genomic instability.

Fermi level equilibration of Ag and Au plasmonic metal nanoparticles supported on graphene oxide.

For the first time, the process of Fermi level equilibration has been studied and compared for plasmonic metal nanoparticles (PMNPs) supported on conducting substrates i.e. graphene oxide (GO) sheets. The extent of Fermi level equilibration has been monitored by recording the changes in the position and intensity of the surface plasmon resonance (SPR) band of Ag and Au PMNPs supported on reduced graphene oxide (rGO). Ag PMNPs supported on rGO show larger variation in the SPR band position and intensity as compared to rGO supported Au PMNPs. The average shift in the chemical potential has been determined through the changes in the SPR band position for Ag, Ag@rGO, Au, and Au@rGO, which are approximately -1812 ± 70 mV, -171 ± 20 mV, -96 ± 8 mV and -29 ± 4 mV, respectively. The calculated values of the shift in chemical potential suggest that Ag and its rGO composite are more prone to Fermi level equilibration as compared to the Au and Au@rGO composite. The electrochemical (galvanostatic) charging/discharging (GCD) measurements also brace the observations from the chemical charging/discharging method with minor variations due to the measurements under two different conditions; particulate films in the case of the former versus the dispersed phase in the case of the latter. Moreover, the average capacitance associated with single nanoparticles (Ag and Au) is estimated using the capacitance values determined from GCD curves and the approximate number of nanoparticles determined from the quantity of PMNPs used in the deposited films for GCD measurements. These values are in close agreement with the quantized double layer capacitance values of monolayer protected clusters reported in the literature. A similar inference is also drawn from the enzyme-less glucose sensing activity of these nanostructures, where Ag and Ag@rGO show better activity in terms of lower values of the limit of detection (LOD) and the limit of quantification (LOQ).