Understanding the Connetion between Epigenetic DNA Methylation and Nucleosome Positioning from Computer Simulations

Cytosine methylation is one of the most important epigenetic marks that regulate the process of gene expression. Here, we have examined the effect of epigenetic DNA methylation on nucleosomal stability using molecular dynamics simulations and elastic deformation models. We found that methylation of CpG steps destabilizes nucleosomes, especially when these are placed in sites where the DNA minor groove faces the histone core. The larger stiffness of methylated CpG steps is a crucial factor behind the decrease in nucleosome stability. Methylation changes the positioning and phasing of the nucleosomal DNA, altering the accessibility of DNA to regulatory proteins, and accordingly gene functionality. Our theoretical calculations highlight a simple physical-based explanation on the foundations of epigenetic signaling

Correlated motions in DNA. Beyond base-pair step models of DNA flexibility.

Traditional mesoscopic models of DNA flexibility use a reductionist-local approach, which assumes that the flexibility of DNA can be expressed as local harmonic movements (at the base-pair step level) in the helical space, ignoring multimodality and correlations in DNA movements, which have in reality a large impact in modulating DNA movements. We present a new multimodal-harmonic correlated model, which takes both contributions into account, providing, with a small computational cost, results of an unprecedented local and global quality. The accuracy of this method and its computational efficiency make it an alternative to explore the dynamics of long segments of DNA, approaching the chromatin range

DNAffinity: a machine-learning approach to predict DNA binding affinities of transcription factors

We present a physics-based machine learning approach to predict in vitro transcription factor binding affinities from structural and mechanical DNA properties directly derived from atomistic molecular dynamics simulations. The method is able to predict affinities obtained with techniques as different as uPBM, gcPBM and HT-SELEX with an excellent performance, much better than existing algorithms. Due to its nature, the method can be extended to epigenetic variants, mismatches, mutations, or any non-coding nucleobases. When complemented with chromatin structure information, our in vitro trained method provides also good estimates of in vivo binding sites in yeast

A multifunctional toolkit for target-directed cancer therapy

Here we present 2shRNA, a shRNA-based nanobinder, which can simultaneously attack two therapeutic targets involved in drug resistance pathways and can additionally bind accessory molecules such as cell targeting peptides or fluorophores. We create 2shRNAs designed to specifically kill HER2+ breast cancer cells in the absence of a transfecting agent

Molecular dynamics modelling of the interaction of a synthetic zinc-finger miniprotein with DNA

We report the modelling of the DNA complex of an artificial miniprotein composed of two zinc finger modules and an AT-hook linking peptide. The computational study provides for the first time a structural view of these types of complexes, dissecting interactions that are key to modulate their stability. The relevance of these interactions was validated experimentally. These results confirm the potential of this type of computational approach for studying peptide–DNA complexes and suggest that they could be very useful for the rational design of non-natural, DNA binding miniproteinsThis work has received financial support from Spanish grants (IJC2019-040358-I funded by MCIN/AEI/10.13039/501100011033 to J. R., PID2019-108624RB-I00 funded by MCIN/AEI/10.13039/501100011033 to J. L. M. and RTI2018-096704-B-100 and PID2021-122478NB-I00 to M. O.), the Consellería de Cultura, Educación e Ordenación Universitaria (Grants 2015-CP082, ED431C-2017/19, ED431C-2021/ 25 and ED431G 2019/03: Centro Singular de Investigación de Galicia accreditation 2019–2022 to J. L. M.) and the European Union (European Regional Development Fund-ERDF corresponding to the multiannual financial framework 2014–2020 to J. L. M.). This work was also supported by the BioExcel-2. Centre of Excellence for Computational Biomolecular Research” (823830, M. O.) and the Instituto de Salud Carlos III–Instituto Nacional de Bioinformática (ISCIII PT 17/0009/0007 co-funded by the Fondo Europeo de Desarrollo Regional, M. O.)S

DNA structure directs positioning of the mitochondrial genome packaging protein Abf2p.

The mitochondrial genome (mtDNA) is assembled into nucleo-protein structures termed nucleoids and maintained differently compared to nuclear DNA, the involved molecular basis remaining poorly understood. In yeast (Saccharomyces cerevisiae), mtDNA is a ∼80 kbp linear molecule and Abf2p, a double HMG-box protein, packages and maintains it. The protein binds DNA in a non-sequence-specific manner, but displays a distinct 'phased-binding' at specific DNA sequences containing poly-adenine tracts (A-tracts). We present here two crystal structures of Abf2p in complex with mtDNA-derived fragments bearing A-tracts. Each HMG-box of Abf2p induces a 90° bend in the contacted DNA, causing an overall U-turn. Together with previous data, this suggests that U-turn formation is the universal mechanism underlying mtDNA compaction induced by HMG-box proteins. Combining this structural information with mutational, biophysical and computational analyses, we reveal a unique DNA binding mechanism for Abf2p where a characteristic N-terminal flag and helix are crucial for mtDNA maintenance. Additionally, we provide the molecular basis for A-tract mediated exclusion of Abf2p binding. Due to high prevalence of A-tracts in yeast mtDNA, this has critical relevance for nucleoid architecture. Therefore, an unprecedented A-tract mediated protein positioning mechanism regulates DNA packaging proteins in the mitochondria, and in combination with DNA-bending and U-turn formation, governs mtDNA compaction

Molecular basis or arginine and lysine DNA sequence-dependent thermo-stability modulation

We have used a variety of theoretical and experimental techniques to study the role of four basic amino acids-Arginine, Lysine, Ornithine and L-2,4-Diaminobutyric acid-on the structure, flexibility and sequence-dependent stability of DNA. We found that the presence of organic ions stabilizes the duplexes and significantly reduces the difference in stability between AT- and GC-rich duplexes with respect to the control conditions. This suggests that these amino acids, ingredients of the primordial soup during abiogenesis, could have helped to equalize the stability of AT- and GC-rich DNA oligomers, facilitating a general noncatalysed self-replication of DNA. Experiments and simulations demonstrate that organic ions have an effect that goes beyond the general electrostatic screening, involving specific interactions along the grooves of the double helix. We conclude that organic ions, largely ignored in the DNA world, should be reconsidered as crucial structural elements far from mimics of small inorganic cations

How B-DNA dynamics decipher sequence-selective protein recognition

The rules governing sequence-specific DNA-protein recognition are under a long-standing debate regarding the prevalence of base versus shape readout mechanisms to explain sequence specificity and of the conformational selection versus induced fit binding paradigms to explain binding-related conformational changes in DNA. Using a combination of atomistic simulations on a subset of representative sequences and mesoscopic simulations at the protein-DNA interactome level, we demonstrate the prevalence of the shape readout model in determining sequence-specificity and of the conformational selection paradigm in defining the general mechanism for binding-related conformational changes in DNA. Our results suggest that the DNA uses a double mechanism to adapt its structure to the protein: it moves along the easiest deformation modes to approach the bioactive conformation, while final adjustments require localized rearrangements at the base-pair step and backbone level. Our study highlights the large impact of B-DNA dynamics in modulating DNA-protein binding

Minorenni vittime di omicidio a Milano (Italia): 1993-2017

This study aims to examine the phenomenon of homicide with victims under 18 years-old in a wide and multiethnic metropolitanarea in the north of Italy. We’re dealing with a type of crime that generates a widespread alarm and a common concern.The data analysis, approached with a multidisciplinary strategy, presented in this paper is based on forensic reports of the Instituteof Legal Medicine of the University of Milan, to provide a detailed framework of the homicides of minors that took place inthe territorial jurisdiction of Milan and Monza Prosecutor’s Office between 1993 and 2017. Quantitative and qualitative analysiswere conducted regarding victims’ socio-demographic characteristics (gender, age, nationality), weapons used, places and modalityof body discovery, murderers, motives of the killing and type of relationship between offenders and victims. Purpose of thispaper is to compare the present set of data with the ones provided by the international literature, as well as make some criminologicalobservations on this matter with a view to preventing the phenomenon. To this end, some representative case studieshave been added, their characteristics and also the relationships between offender and victim have been discussed.Questo studio esamina il fenomeno dell'omicidio con vittime di età inferiore ai 18 anni in una vasta e multietnica area metropolitanadel nord Italia, un tipo di crimine che genera allarme e preoccupazione. L'analisi dei dati, affrontata con una metodologia multidisciplinare,è basata sui verbali autoptici dell'Istituto di Medicina Legale dell'Università di Milano, al fine di fornire un quadro dettagliatodegli omicidi con vittima minorenne che si sono verificati nella giurisdizione territoriale della Procura di Milano e Monzatra il 1993 e il 2017. Sono state condotte analisi quantitative e qualitative sulle vittime, quali le caratteristiche socio-demografiche(genere, età, nazionalità), le armi utilizzate, i luoghi e le modalità di rinvenimento del corpo, le caratteristiche dell’omicida, i motividell'uccisione e il tipo di relazione tra criminale e vittima. Scopo di questo studio è confrontare l'attuale insieme di dati con quelliforniti dalla letteratura internazionale, nonché porre alcune considerazioni di carattere preventivo. A tal fine, sono stati presentatianche alcuni casi studio rappresentativi, discutendone le caratteristiche peculiari e le relazioni tra l'autore del reato e la vittima

The Impact of the HydroxyMethylCytosine epigenetic signature on DNA structure and function.

Funder: Programa de Desarrollo de las Ciencias BasicasFunder: Institució Catalana de Recerca i Estudis AvancatsFunder: Sistema Nacional de Investigadores, Agencia Nacional de Investigación e Innovación, UruguayFunder: Government of SpainWe present a comprehensive, experimental and theoretical study of the impact of 5-hydroxymethylation of DNA cytosine. Using molecular dynamics, biophysical experiments and NMR spectroscopy, we found that Ten-Eleven translocation (TET) dioxygenases generate an epigenetic variant with structural and physical properties similar to those of 5-methylcytosine. Experiments and simulations demonstrate that 5-methylcytosine (mC) and 5-hydroxymethylcytosine (hmC) generally lead to stiffer DNA than normal cytosine, with poorer circularization efficiencies and lower ability to form nucleosomes. In particular, we can rule out the hypothesis that hydroxymethylation reverts to unmodified cytosine physical properties, as hmC is even more rigid than mC. Thus, we do not expect dramatic changes in the chromatin structure induced by differences in physical properties between d(mCpG) and d(hmCpG). Conversely, our simulations suggest that methylated-DNA binding domains (MBDs), associated with repression activities, are sensitive to the substitution d(mCpG) ➔ d(hmCpG), while MBD3 which has a dual activation/repression activity is not sensitive to the d(mCpG) d(hmCpG) change. Overall, while gene activity changes due to cytosine methylation are the result of the combination of stiffness-related chromatin reorganization and MBD binding, those associated to 5-hydroxylation of methylcytosine could be explained by a change in the balance of repression/activation pathways related to differential MBD binding