Chromosome architecture needs to be investigated in relation with the chemical function of DNA. The kinetics of gene expression, DNA replication, and repair are driven by the mechanisms by which a functional nuclear protein finds its substrate in the nucleus. Single-particle tracking (SPT) is a method to quantify fluorescent molecules dynamics from the tracks of the single molecules recorded by high-resolution microscopes. SPT offers direct observation of the movement and single-molecule resolution. Usually SPT is performed on membranes because of higher contrast. Here, we introduce a novel method to record the trajectories of weakly fluorescent molecules in the nucleus of living cells. I-SPT uses some specific detection and analysis tools to enable the computation of reliable statistics on nuclear particle movement.

• MeSH
• buněčné jádro metabolismus   MeSH
• buněčné linie MeSH
• lidé MeSH
• lidské chromozomy genetika   ultrastruktura   MeSH
• počítačové zpracování obrazu MeSH
• replikace DNA MeSH
• zobrazení jednotlivé molekuly metody   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Cryo-electron microscopy has established as a mature structural biology technique to elucidate the three-dimensional structure of biological macromolecules. The Coulomb potential of the sample is imaged by an electron beam, and fast semi-conductor detectors produce movies of the sample under study. These movies have to be further processed by a whole pipeline of image-processing algorithms that produce the final structure of the macromolecule. In this chapter, we illustrate this whole processing pipeline putting in value the strength of "meta algorithms," which are the combination of several algorithms, each one with different mathematical rationale, in order to distinguish correctly from incorrectly estimated parameters. We show how this strategy leads to superior performance of the whole pipeline as well as more confident assessments about the reconstructed structures. The "meta algorithms" strategy is common to many fields and, in particular, it has provided excellent results in bioinformatics. We illustrate this combination using the workflow engine, Scipion.

• MeSH
• algoritmy * MeSH
• elektronová kryomikroskopie metody   MeSH
• makromolekulární látky ultrastruktura   MeSH
• molekulární biologie metody   MeSH
• počítačové zpracování obrazu metody   MeSH
• průběh práce MeSH
• výpočetní biologie MeSH
• zobrazení jednotlivé molekuly metody   MeSH
• zobrazování trojrozměrné metody   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

RECQ5 is one of five RecQ helicases found in humans and is thought to participate in homologous DNA recombination by acting as a negative regulator of the recombinase protein RAD51. Here, we use kinetic and single molecule imaging methods to monitor RECQ5 behavior on various nucleoprotein complexes. Our data demonstrate that RECQ5 can act as an ATP-dependent single-stranded DNA (ssDNA) motor protein and can translocate on ssDNA that is bound by replication protein A (RPA). RECQ5 can also translocate on RAD51-coated ssDNA and readily dismantles RAD51-ssDNA filaments. RECQ5 interacts with RAD51 through protein-protein contacts, and disruption of this interface through a RECQ5-F666A mutation reduces translocation velocity by ∼50%. However, RECQ5 readily removes the ATP hydrolysis-deficient mutant RAD51-K133R from ssDNA, suggesting that filament disruption is not coupled to the RAD51 ATP hydrolysis cycle. RECQ5 also readily removes RAD51-I287T, a RAD51 mutant with enhanced ssDNA-binding activity, from ssDNA. Surprisingly, RECQ5 can bind to double-stranded DNA (dsDNA), but it is unable to translocate. Similarly, RECQ5 cannot dismantle RAD51-bound heteroduplex joint molecules. Our results suggest that the roles of RECQ5 in genome maintenance may be regulated in part at the level of substrate specificity.

• MeSH
• adenosintrifosfát metabolismus   MeSH
• bodová mutace MeSH
• helikasy RecQ genetika   metabolismus   ultrastruktura   MeSH
• homologní rekombinace * MeSH
• hydrolýza MeSH
• jednovláknová DNA metabolismus   ultrastruktura   MeSH
• kinetika MeSH
• lidé MeSH
• mikroskopie atomárních sil MeSH
• missense mutace MeSH
• molekulární motory metabolismus   ultrastruktura   MeSH
• rekombinantní fúzní proteiny metabolismus   MeSH
• rekombinantní proteiny metabolismus   MeSH
• rekombinasa Rad51 genetika   metabolismus   MeSH
• replikační protein A metabolismus   MeSH
• substrátová specifita MeSH
• zobrazení jednotlivé molekuly * MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Research Support, N.I.H., Extramural MeSH

RNA-binding proteins (RBPs) are critical to posttranscriptional gene regulation. Therefore, characterization of the RNA molecules bound by RBPs in vivo represent a key step in elucidating their function. The recently developed iCLIP technique allows single nucleotide resolution of the RNA binding footprints of RBPs. We present the iCLIP technique modified for its application to Trypanosoma brucei and most likely other kinetoplastid flagellates. By using the immuno- or affinity purification approach, it was successfully applied to the analysis of several RBPs. Furthermore, we also provide a detailed description of the iCLIP/iCLAP protocol that shall be particularly suitable for the studies of trypanosome RBPs.

• MeSH
• imunoprecipitace metody   MeSH
• nukleotidy genetika   metabolismus   MeSH
• parazitologie metody   MeSH
• proteiny vázající RNA analýza   genetika   metabolismus   MeSH
• protozoální proteiny analýza   genetika   metabolismus   MeSH
• RNA protozoální genetika   metabolismus   MeSH
• RNA genetika   metabolismus   MeSH
• Trypanosoma brucei brucei genetika   MeSH
• ultrafialové záření MeSH
• vazba proteinů genetika   účinky záření   MeSH
• vazebná místa genetika   MeSH
• zobrazení jednotlivé molekuly metody   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Classical models of gene expression were built using genetics and biochemistry. Although these approaches are powerful, they have very limited consideration of the spatial and temporal organization of gene expression. Although the spatial organization and dynamics of RNA polymerase II (RNAPII) transcription machinery have fundamental functional consequences for gene expression, its detailed studies have been abrogated by the limits of classical light microscopy for a long time. The advent of super-resolution microscopy (SRM) techniques allowed for the visualization of the RNAPII transcription machinery with nanometer resolution and millisecond precision. In this review, we summarize the recent methodological advances in SRM, focus on its application for studies of the nanoscale organization in space and time of RNAPII transcription, and discuss its consequences for the mechanistic understanding of gene expression.

• MeSH
• fluorescenční mikroskopie * metody   MeSH
• genetická transkripce * MeSH
• lidé MeSH
• regulace genové exprese * MeSH
• RNA-polymerasa II metabolismus   MeSH
• transkripční faktory metabolismus   MeSH
• vazba proteinů MeSH
• zobrazení jednotlivé molekuly metody   MeSH
• zvířata MeSH
• Check Tag
• lidé MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• přehledy MeSH

Membrane-bound pyrophosphatases couple the hydrolysis of inorganic pyrophosphate to the pumping of ions (sodium or protons) across a membrane in order to generate an electrochemical gradient. This class of membrane protein is widely conserved across plants, fungi, archaea, and bacteria, but absent in multicellular animals, making them a viable target for drug design against protozoan parasites such as Plasmodium falciparum. An excellent understanding of many of the catalytic states throughout the enzymatic cycle has already been afforded by crystallography. However, the dynamics and kinetics of the catalytic cycle between these static snapshots remain to be elucidated. Here, we employ single-molecule Förster resonance energy transfer (FRET) measurements to determine the dynamic range and frequency of conformations available to the enzyme in a lipid bilayer during the catalytic cycle. First, we explore issues related to the introduction of fluorescent dyes by cysteine mutagenesis; we discuss the importance of residue selection for dye attachment, and the balance between mutating areas of the protein that will provide useful dynamics while not altering highly conserved residues that could disrupt protein function. To complement and guide the experiments, we used all-atom molecular dynamics simulations and computational methods to estimate FRET efficiency distributions for dye pairs at different sites in different protein conformational states. We present preliminary single-molecule FRET data that points to insights about the binding modes of different membrane-bound pyrophosphatase substrates and inhibitors.

• MeSH
• bakteriální proteiny chemie   genetika   izolace a purifikace   metabolismus   MeSH
• buněčná membrána metabolismus   MeSH
• enzymatické testy přístrojové vybavení   metody   MeSH
• fluorescenční barviva chemie   MeSH
• fluorescenční mikroskopie přístrojové vybavení   metody   MeSH
• mutageneze MeSH
• protozoální proteiny chemie   genetika   izolace a purifikace   metabolismus   MeSH
• pyrofosfatasy chemie   genetika   izolace a purifikace   metabolismus   MeSH
• racionální návrh léčiv MeSH
• rekombinantní proteiny chemie   genetika   izolace a purifikace   metabolismus   MeSH
• rezonanční přenos fluorescenční energie přístrojové vybavení   metody   MeSH
• Saccharomyces cerevisiae MeSH
• sekvenční seřazení MeSH
• simulace molekulární dynamiky * MeSH
• software MeSH
• zobrazení jednotlivé molekuly přístrojové vybavení   metody   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Quantitative genomic mapping of DNA damage may provide insights into the underlying mechanisms of damage and repair. Sequencing based approaches are bound to the limitations of PCR amplification bias and read length which hamper both the accurate quantitation of damage events and the ability to map them to structurally complex genomic regions. Optical Genome mapping in arrays of parallel nanochannels allows physical extension and genetic profiling of millions of long genomic DNA fragments, and has matured to clinical utility for characterization of complex structural aberrations in cancer genomes. Here we present a new mapping modality, Repair-Assisted Damage Detection - Optical Genome Mapping (RADD-OGM), a method for single-molecule level mapping of DNA damage on a genome-wide scale. Leveraging ultra-long reads to assemble the complex structure of a sarcoma cell-line genome, we mapped the genomic distribution of oxidative DNA damage, identifying regions more susceptible to DNA oxidation. We also investigated DNA repair by allowing cells to repair chemically induced DNA damage, pinpointing locations of concentrated repair activity, and highlighting variations in repair efficiency. Our results showcase the potential of the method for toxicogenomic studies, mapping the effect of DNA damaging agents such as drugs and radiation, as well as following specific DNA repair pathways by selective induction of DNA damage. The facile integration with optical genome mapping enables performing such analyses even in highly rearranged genomes such as those common in many cancers, a challenging task for sequencing-based approaches.

• MeSH
• bromičnany toxicita   MeSH
• lidé MeSH
• mapování chromozomů * přístrojové vybavení   metody   MeSH
• mikrofluidní analytické techniky * přístrojové vybavení   metody   MeSH
• nádorové buněčné linie MeSH
• nanotechnologie * přístrojové vybavení   metody   MeSH
• oprava DNA genetika   MeSH
• oxidační stres účinky léků   genetika   MeSH
• poškození DNA * genetika   MeSH
• regulace genové exprese MeSH
• stanovení celkové genové exprese MeSH
• toxikogenetika * přístrojové vybavení   metody   MeSH
• variabilita počtu kopií segmentů DNA MeSH
• zobrazení jednotlivé molekuly * přístrojové vybavení   metody   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH

DNA double stranded breaks (DSBs) are the most serious type of lesions introduced into chromatin by ionizing radiation. During DSB repair, cells recruit different proteins to the damaged sites in a manner dependent on local chromatin structure, DSB location in the nucleus, and the repair pathway entered. 53BP1 is one of the important players participating in repair pathway decision of the cell. Although many molecular biology details have been investigated, the architecture of 53BP1 repair foci and its development during the post-irradiation time, especially the period of protein recruitment, remains to be elucidated. Super-resolution light microscopy is a powerful new tool to approach such studies in 3D-conserved cell nuclei. Recently, we demonstrated the applicability of single molecule localization microscopy (SMLM) as one of these highly resolving methods for analyses of dynamic repair protein distribution and repair focus internal nano-architecture in intact cell nuclei. In the present study, we focused our investigation on 53BP1 foci in differently radio-resistant cell types, moderately radio-resistant neonatal human dermal fibroblasts (NHDF) and highly radio-resistant U87 glioblastoma cells, exposed to high-LET 15N-ion radiation. At given time points up to 24 h post irradiation with doses of 1.3 Gy and 4.0 Gy, the coordinates and spatial distribution of fluorescently tagged 53BP1 molecules was quantitatively evaluated at the resolution of 10⁻20 nm. Clusters of these tags were determined as sub-units of repair foci according to SMLM parameters. The formation and relaxation of such clusters was studied. The higher dose generated sufficient numbers of DNA breaks to compare the post-irradiation dynamics of 53BP1 during DSB processing for the cell types studied. A perpendicular (90°) irradiation scheme was used with the 4.0 Gy dose to achieve better separation of a relatively high number of particle tracks typically crossing each nucleus. For analyses along ion-tracks, the dose was reduced to 1.3 Gy and applied in combination with a sharp angle irradiation (10° relative to the cell plane). The results reveal a higher ratio of 53BP1 proteins recruited into SMLM defined clusters in fibroblasts as compared to U87 cells. Moreover, the speed of foci and thus cluster formation and relaxation also differed for the cell types. In both NHDF and U87 cells, a certain number of the detected and functionally relevant clusters remained persistent even 24 h post irradiation; however, the number of these clusters again varied for the cell types. Altogether, our findings indicate that repair cluster formation as determined by SMLM and the relaxation (i.e., the remaining 53BP1 tags no longer fulfill the cluster definition) is cell type dependent and may be functionally explained and correlated to cell specific radio-sensitivity. The present study demonstrates that SMLM is a highly appropriate method for investigations of spatiotemporal protein organization in cell nuclei and how it influences the cell decision for a particular repair pathway at a given DSB site.

• MeSH
• 53BP1 metabolismus   MeSH
• konfokální mikroskopie metody   MeSH
• kultivované buňky MeSH
• lidé MeSH
• nádorové buněčné linie MeSH
• rekombinační oprava DNA * MeSH
• transport proteinů MeSH
• zobrazení jednotlivé molekuly metody   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH

In cancer therapy, the application of (fractionated) harsh radiation treatment is state of the art for many types of tumors. However, ionizing radiation is a "double-edged sword"-it can kill the tumor but can also promote the selection of radioresistant tumor cell clones or even initiate carcinogenesis in the normal irradiated tissue. Individualized radiotherapy would reduce these risks and boost the treatment, but its development requires a deep understanding of DNA damage and repair processes and the corresponding control mechanisms. DNA double strand breaks (DSBs) and their repair play a critical role in the cellular response to radiation. In previous years, it has become apparent that, beyond genetic and epigenetic determinants, the structural aspects of damaged chromatin (i.e., not only of DSBs themselves but also of the whole damage-surrounding chromatin domains) form another layer of complex DSB regulation. In the present article, we summarize the application of super-resolution single molecule localization microscopy (SMLM) for investigations of these structural aspects with emphasis on the relationship between the nano-architecture of radiation-induced repair foci (IRIFs), represented here by γH2AX foci, and their chromatin environment. Using irradiated HeLa cell cultures as an example, we show repair-dependent rearrangements of damaged chromatin and analyze the architecture of γH2AX repair clusters according to topological similarities. Although HeLa cells are known to have highly aberrant genomes, the topological similarity of γH2AX was high, indicating a functional, presumptively genome type-independent relevance of structural aspects in DSB repair. Remarkably, nano-scaled chromatin rearrangements during repair depended both on the chromatin domain type and the treatment. Based on these results, we demonstrate how the nano-architecture and topology of IRIFs and chromatin can be determined, point to the methodological relevance of SMLM, and discuss the consequences of the observed phenomena for the DSB repair network regulation or, for instance, radiation treatment outcomes.

• MeSH
• chromatin genetika   ultrastruktura   MeSH
• dvouřetězcové zlomy DNA účinky záření   MeSH
• HeLa buňky MeSH
• ionizující záření MeSH
• lidé MeSH
• mikroskopie metody   MeSH
• nádorové buněčné linie MeSH
• nádory genetika   MeSH
• oprava DNA genetika   účinky záření   MeSH
• poškození DNA genetika   účinky záření   MeSH
• zobrazení jednotlivé molekuly metody   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH

• MeSH
• elektronová mikroskopie MeSH
• fotosyntéza MeSH
• multienzymové komplexy fyziologie   izolace a purifikace   ultrastruktura   MeSH
• velikost částic metody   MeSH