The mutation/deletion of the hereditary material in the cell nuclei is a chronic biochemical hazard; in fact, nuclear DNA faces tens of lesions from metabolic intermediates, hydrolytic reactions and external vectors a minute. The canonical lesions of DNA involve the DNA backbone as well as the nucleic bases and are mostly associated with reversible chemical modifications. However, the radiation field from beams of accelerated ions accounts for a dense streak of collisions and reactions with the DNA molecule, thereby achieving lethal clusters of elemental lesions. Double strand breaks (DSB), i.e., the cleft of the DNA backbone over both strands, are hazardous fractures of the chromatin fold associated with the radiation field, underlying cytotoxic outcomes and chromosomal aberrations. Eukaryotic cells, however, rejoin the fractured DNA moieties from DSB events via an apt enzymatic machinery, or the DDR. Prior to the deployment of enzymatic effectors, host enzyme sensors engage the DNA termini in reversible supramolecular assemblies, which requires that the fractured DNA moieties be fully exposed. The in silico assessments of the early layout of DNA lesions by radiations have defined DSBs as the closely associated modifications of the DNA backbone by means of “coarse” criteria, that is, within an arbitrary distance of the two clefts. However, the diverse DSB motifs, i.e. at a strand break distance of zero to several nucleotides, account for a different contact interface between the DNA termini, thus modulating the dynamics of the lesion sites. Moreover, it is reckoned that in the absence of excess external stimuli, far-distanced DSBs may not fracture the broken DNA moieties by thermal dissociation, within the characteristic timescales of the DDR activity. This thesis elaborate tackles the in silico assessment of the distribution of DSBs in a chromatin-like fold and the local mechanical strain enforced by blunt DSBs, by means of state-of-the-art Monte-Carlo track structure tools and classical molecular dynamics. We infer that i) a Poisson fit describes the spectrum of DSB motifs by the direct effect of accelerated hydrogen ions (H+) at a Bragg peak relevant energy range (500 keV - 5 MeV) and, notably, we observe a bias towards short-distanced, staggered DSBs; ii) the nucleosome fold, i.e. the elemental unit of the chromatin hierarchical framework, exerts an excess kinetic barrier on the disruption of DSBs, which is not observed in linear DNA, mediated by the contact interface between DNA and the core histone fold. In conclusion, we remark that in the absence of further data from in vitro and in vivo assessments, the (kinetic, thermodynamic) inferences about the thermal and mechanical resilience of broken DNA frameworks are as reliable as the force fields underneath; in fact, it is debated whether all-atom force fields and water models overestimate the force of the intermolecular contacts and over-stabilize the DNA double helix.
| Identifer | oai:union.ndltd.org:unitn.it/oai:iris.unitn.it:11572/338714 |
| Date | 21 April 2022 |
| Creators | Petrolli, Lorenzo |
| Contributors | Petrolli, Lorenzo, Lattanzi, Gianluca, Scifoni, Emanuele |
| Publisher | Università degli studi di Trento, place:TRENTO |
| Source Sets | Università di Trento |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/doctoralThesis |
| Rights | info:eu-repo/semantics/openAccess |
| Relation | firstpage:1, lastpage:110, numberofpages:110 |
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