Trypanosoma brucei BRCA2 acts in a life cycle-specific genome stability process and dictates BRC repeat number-dependent RAD51 subnuclear dynamics

Trypanosoma brucei survives in mammals through antigenic variation, which is driven by RAD51-directed homologous recombination of Variant Surface Glycoproteins (VSG) genes, most of which reside in a subtelomeric repository of >1000 silent genes. A key regulator of RAD51 is BRCA2, which in T. brucei contains a dramatic expansion of a motif that mediates interaction with RAD51, termed the BRC repeats. BRCA2 mutants were made in both tsetse fly-derived and mammal-derived T. brucei, and we show that BRCA2 loss has less impact on the health of the former. In addition, we find that genome instability, a hallmark of BRCA2 loss in other organisms, is only seen in mammal-derived T. brucei. By generating cells expressing BRCA2 variants with altered BRC repeat numbers, we show that the BRC repeat expansion is crucial for RAD51 subnuclear dynamics after DNA damage. Finally, we document surprisingly limited co-localization of BRCA2 and RAD51 in the T. brucei nucleus, and we show that BRCA2 mutants display aberrant cell division, revealing a function distinct from BRC-mediated RAD51 interaction. We propose that BRCA2 acts to maintain the huge VSG repository of T. brucei, and this function has necessitated the evolution of extensive RAD51 interaction via the BRC repeats, allowing re-localization of the recombinase to general genome damage when needed

Are SMC complexes loop extruding factors? Linking theory with fact

The extreme length of chromosomal DNA requires organizing mechanisms to both promote functional genetic interactions and ensure faithful chromosome segregation when cells divide. Microscopy and genome‐wide contact frequency analyses indicate that intra‐chromosomal looping of DNA is a primary pathway of chromosomal organization during all stages of the cell cycle. DNA loop extrusion has emerged as a unifying model for how chromosome loops are formed in cis in different genomic contexts and cell cycle stages. The highly conserved family of SMC complexes have been found to be required for DNA cis‐looping and have been suggested to be the enzymatic core of loop extruding machines. Here, the current body of evidence available for the in vivo and in vitro action of SMC complexes is discussed and compared to the predictions made by the loop extrusion model. How SMC complexes may differentially act on chromatin to generate DNA loops and how they could work to generate the dynamic and functionally appropriate organization of DNA in cells is explored

Unrevealing mechanism of the thermal tautomerization of avobenzone by means of quantum chemical computations

Avobenzone (4-tert-butyl-4’-methoxydibenzoylmethane) is one of the most widely used UVA filters in cosmetic sunscreens. Reactivity of avobenzone is complex and challenging to understand, due to a presence of transient tautomers. In this contribution we study chelated enol, rotamer and keto tautomers of a reduced model of avobenzone which are involved in keto-enol tautomerization. Two thermal tautomerization mechanisms are postulated and their transient structures are discussed. The computed vertical and adiabatic electronic excitation energies of tautomers provide an additional insight into excited state properties of the tautomers. [Projekat Ministarstva nauke Republike Srbije, br. 172040 i br. ON171017

Rhodium(III) in a cage of the 1,3-propanediamine-N,N,N′-triacetate chelate: X-ray structure, solution equilibria, computational study and biological behavior

Two new octahedral Rh(III) complexes that are potential chemotherapeutic agents have been synthesized from the 1,3-propanediamine-N,N,N’-triacetate ligand (1,3-pd3a): [Rh(1,3-pd3a)(H2O)]·2H2O (1) and Na[Rh(1,3-pd3a)Cl]·2H2O (2). Both complexes were characterized by IR, UV–Vis and NMR spectroscopy, as well as elemental analysis. Only the structure of 2 was determined by a single crystal X-ray diffraction study. The asymmetric unit contains the negatively charged rhodium complex, a sodium ion and two water molecules. The positions of the carboxylate groups define the cis-polar geometry. DFT calculations on 1 and 2 have also been done to confirm experimental results. In order to determine the protonation constants of 1,3-H3pd3a, stability constants and the stoichiometry of the complexes in aqueous solution, pH-potentiometry and UV–Vis spectrophotometry were used. Docking of 1 to human serum albumin (HSA) gives the reasonable assumption that this complex can be easily transported to the target cells. The complexes, as well as the 1,3-pd3a and ed3a ligands, were tested against various cancer and one normal human cell lines. Complex 2 and both ligands display significant cytotoxicity against the HeLa cancer cell line, while 1 shows good antitumor activity against MCF-7. Flow cytometry analysis showed the apoptotic death of the cells with cell cycle arrest in the G2/M phase (Na[Rh(1,3-pd3a)Cl]·2H2O) and G0/G1 phase (1,3-pd3a)