Kink-turns are highly bent internal loop motifs commonly found in the ribosome and other RNA complexes. They frequently act as binding sites for proteins and mediate tertiary interactions in larger RNA structures. Kink-turns have been a topic of intense research, but their elastic properties in the folded state are still poorly understood. Here we use extensive all-atom molecular dynamics simulations to parameterize a model of kink-turn in which the two flanking helical stems are represented by effective rigid bodies. Time series of the full set of six interhelical coordinates enable us to extract minimum energy shapes and harmonic stiffness constants for kink-turns from different RNA functional classes. The analysis suggests that kink-turns exhibit isotropic bending stiffness but are highly anisotropic with respect to lateral displacement of the stems. The most flexible lateral displacement mode is perpendicular to the plane of the static bend. These results may help understand the structural adaptation and mechanical signal transmission by kink-turns in complex natural and artificial RNA structures.

• MeSH
• Nucleic Acid Conformation MeSH
• Ribosomes metabolism   MeSH
• RNA * chemistry   MeSH
• Molecular Dynamics Simulation * MeSH
• Binding Sites MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• RNA * MeSH

Mutations can be induced by environmental factors but also arise spontaneously during DNA replication or due to deamination of methylated cytosines at CpG dinucleotides. Sites where mutations occur with higher frequency than would be expected by chance are termed hotspots while sites that contain mutations rarely are termed coldspots. Mutations are permanently scanned and repaired by repair systems. Among them, the mismatch repair targets base pair mismatches, which are discriminated from canonical base pairs by probing altered elasticity of DNA. Using biased molecular dynamics simulations, we investigated the elasticity of coldspots and hotspots motifs detected in human genes associated with inherited disorders, and also of motifs with Czech population hotspots and de novo mutations. Main attention was paid to mutations leading to G/T and A+/C pairs. We observed that hotspots without CpG/CpHpG sequences are less flexible than coldspots, which indicates that flexible sequences are more effectively repaired. In contrary, hotspots with CpG/CpHpG sequences exhibited increased flexibility as coldspots. Their mutability is more likely related to spontaneous deamination of methylated cytosines leading to C > T mutations, which are primarily targeted by base excision repair. We corroborated conclusions based on computer simulations by measuring melting curves of hotspots and coldspots containing G/T mismatch.

• Keywords
• DNA bending, Muts protein, free energy calculations, hotspots–coldspots, mutations,
• MeSH
• CpG Islands MeSH
• DNA chemistry   genetics   MeSH
• Humans MeSH
• Mutation * MeSH
• Nucleotide Motifs * MeSH
• Molecular Dynamics Simulation * MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• DNA MeSH

Adenosine to inosine (A⁻I) editing is the most common modification of double-stranded RNA (dsRNA). This change is mediated by adenosine deaminases acting on RNA (ADARs) enzymes with a preference of U>A>C>G for 5′ neighbor and G>C=A>U or G>C>U=A for 3′ neighbor. A⁻I editing occurs most frequently in the non-coding regions containing repetitive elements such as ALUs. It leads to disruption of RNA duplex structure, which prevents induction of innate immune response. We employed standard and biased molecular dynamics (MD) simulations to analyze the behavior of RNA duplexes with single and tandem inosine⁻uracil (I⁻U) base pairs in different sequence context. Our analysis showed that the I⁻U pairs induce changes in base pair and base pair step parameters and have different dynamics when compared with standard canonical base pairs. In particular, the first I⁻U pair from tandem I⁻U/I⁻U systems exhibited increased dynamics depending on its neighboring 5′ base. We discovered that UII sequence, which is frequently edited, has lower flexibility compared with other sequences (AII, GII, CII), hence it only modestly disrupts dsRNA. This might indicate that the UAA motifs in ALUs do not have to be sufficiently effective in preventing immune signaling.

• Keywords
• I-U base pairs, adenosine to inosine editing, dsRNA, molecular dynamics simulations,
• Publication type
• Journal Article MeSH

Mutations in human genes can be responsible for inherited genetic disorders and cancer. Mutations can arise due to environmental factors or spontaneously. It has been shown that certain DNA sequences are more prone to mutate. These sites are termed hotspots and exhibit a higher mutation frequency than expected by chance. In contrast, DNA sequences with lower mutation frequencies than expected by chance are termed coldspots. Mutation hotspots are usually derived from a mutation spectrum, which reflects particular population where an effect of a common ancestor plays a role. To detect coldspots/hotspots unaffected by population bias, we analysed the presence of germline mutations obtained from HGMD database in the 5-nucleotide segments repeatedly occurring in genes associated with common inherited disorders, in particular, the PAH, LDLR, CFTR, F8, and F9 genes. Statistically significant sequences (mutational motifs) rarely associated with mutations (coldspots) and frequently associated with mutations (hotspots) exhibited characteristic sequence patterns, e.g. coldspots contained purine tract while hotspots showed alternating purine-pyrimidine bases, often with the presence of CpG dinucleotide. Using molecular dynamics simulations and free energy calculations, we analysed the global bending properties of two selected coldspots and two hotspots with a G/T mismatch. We observed that the coldspots were inherently more flexible than the hotspots. We assume that this property might be critical for effective mismatch repair as DNA with a mutation recognized by MutSα protein is noticeably bent.

• MeSH
• DNA chemistry   genetics   MeSH
• Factor VIII genetics   MeSH
• Genetic Predisposition to Disease MeSH
• Nucleic Acid Conformation MeSH
• Receptors, LDL genetics   MeSH
• Humans MeSH
• Models, Molecular MeSH
• Nucleotide Motifs MeSH
• Cystic Fibrosis Transmembrane Conductance Regulator genetics   MeSH
• Molecular Dynamics Simulation MeSH
• Germ-Line Mutation * MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• CFTR protein, human MeSH Browser
• DNA MeSH
• F8 protein, human MeSH Browser
• Factor VIII MeSH
• Receptors, LDL MeSH
• LDLR protein, human MeSH Browser
• Cystic Fibrosis Transmembrane Conductance Regulator MeSH

Oxidatively-generated interstrand cross-links rank among the most deleterious DNA lesions. They originate from abasic sites, whose aldehyde group can form a covalent adduct after condensation with the exocyclic amino group of purines, sometimes with remarkably high yields. We use explicit solvent molecular dynamics simulations to unravel the structures and mechanical properties of two DNA sequences containing an interstrand cross-link. Our simulations palliate the absence of experimental structural and stiffness information for such DNA lesions and provide an unprecedented insight into the DNA embedding of lesions that represent a major challenge for DNA replication, transcription and gene regulation by preventing strand separation. Our results based on quantum chemical calculations also suggest that the embedding of the ICL within the duplex can tune the reaction profile, and hence can be responsible for the high difference in yields of formation.

• MeSH
• Algorithms MeSH
• DNA chemistry   MeSH
• Nucleic Acid Conformation * MeSH
• Models, Molecular MeSH
• Molecular Structure MeSH
• Molecular Dynamics Simulation * MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• DNA MeSH