| 1. |
- Feng, Bobo, 1987, et al.
(author)
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Hydrophobic catalysis and a potential biological role of DNA unstacking induced by environment effects
- 2019
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In: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 116:35, s. 17169-17174
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Journal article (peer-reviewed)abstract
- Hydrophobic base stacking is a major contributor to DNA double-helix stability. We report the discovery of specific unstacking effects in certain semihydrophobic environments. Water-miscible ethylene glycol ethers are found to modify structure, dynamics, and reactivity of DNA by mechanisms possibly related to a biologically relevant hydrophobic catalysis. Spectroscopic data and optical tweezers experiments show that base-stacking energies are reduced while base-pair hydrogen bonds are strengthened. We propose that a modulated chemical potential of water can promote “longitudinal breathing” and the formation of unstacked holes while base unpairing is suppressed. Flow linear dichroism in 20% diglyme indicates a 20 to 30% decrease in persistence length of DNA, supported by an increased flexibility in single-molecule nanochannel experiments in poly(ethylene glycol). A limited (3 to 6%) hyperchromicity but unaffected circular dichroism is consistent with transient unstacking events while maintaining an overall average B-DNA conformation. Further information about unstacking dynamics is obtained from the binding kinetics of large thread-intercalating ruthenium complexes, indicating that the hydrophobic effect provides a 10 to 100 times increased DNA unstacking frequency and an “open hole” population on the order of 10−2 compared to 10−4 in normal aqueous solution. Spontaneous DNA strand exchange catalyzed by poly(ethylene glycol) makes us propose that hydrophobic residues in the L2 loop of recombination enzymes RecA and Rad51 may assist gene recombination via modulation of water activity near the DNA helix by hydrophobic interactions, in the manner described here. We speculate that such hydrophobic interactions may have catalytic roles also in other biological contexts, such as in polymerases.
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| 2. |
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| 3. |
- Jiang, Kai, 1988, et al.
(author)
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Alpha-Synuclein Modulates the Physical Properties of DNA
- 2018
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In: Chemistry - A European Journal. - : Wiley. - 1521-3765 .- 0947-6539. ; 24:58, s. 15685-15690
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Journal article (peer-reviewed)abstract
- Published by Wiley-VCH Verlag GmbH & Co. KGaA. Fundamental research on Parkinson's disease (PD) most often focuses on the ability of α-synuclein (aS) to form oligomers and amyloids, and how such species promote brain cell death. However, there are indications that aS also plays a gene-regulatory role in the cell nucleus. Here, the interaction between monomeric aS and DNA in vitro has been investigated with single-molecule techniques. Using a nanofluidic channel system, it was discovered that aS binds to DNA and by studying the DNA–protein complexes at different confinements we determined that aS binding increases the persistence length of DNA from 70 to 90 nm at high coverage. By atomic force microscopy it was revealed that at low protein-to-DNA ratio, the aS binding occurs as small protein clusters scattered along the DNA; at high protein-to-DNA ratio, the DNA is fully covered by protein. As DNA-aS interactions may play roles in PD, it is of importance to characterize biophysical properties of such complexes in detail.
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| 4. |
- Jiang, Kai, 1988, et al.
(author)
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Annealing of ssDNA and compaction of dsDNA by the HIV-1 nucleocapsid and Gag proteins visualized using nanofluidic channels
- 2019
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In: Quarterly Reviews of Biophysics. - 1469-8994 .- 0033-5835. ; 52, s. e2-e2
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Journal article (peer-reviewed)abstract
- The nucleocapsid protein NC is a crucial component in the human immunodeficiency virus type 1 life cycle. It functions both in its processed mature form and as part of the polyprotein Gag that plays a key role in the formation of new viruses. NC can protect nucleic acids (NAs) from degradation by compacting them to a dense coil. Moreover, through its NA chaperone activity, NC can also promote the most stable conformation of NAs. Here, we explore the balance between these activities for NC and Gag by confining DNA-protein complexes in nanochannels. The chaperone activity is visualized as concatemerization and circularization of long DNA via annealing of short single-stranded DNA overhangs. The first ten amino acids of NC are important for the chaperone activity that is almost completely absent for Gag. Gag condenses DNA more efficiently than mature NC, suggesting that additional residues of Gag are involved. Importantly, this is the first single DNA molecule study of full-length Gag and we reveal important differences to the truncated Δ-p6 Gag that has been used before. In addition, the study also highlights how nanochannels can be used to study reactions on ends of long single DNA molecules, which is not trivial with competing single DNA molecule techniques.
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| 5. |
- Jiang, Kai, 1988, et al.
(author)
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C-terminal truncation of α-synuclein alters DNA structure from extension to compaction
- 2021
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In: Biochemical and Biophysical Research Communications. - : Elsevier BV. - 1090-2104 .- 0006-291X. ; 568, s. 43-47
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Journal article (peer-reviewed)abstract
- Parkinson's disease (PD) is linked to aggregation of the protein α-synuclein (aS) into amyloid fibers. aS is proposed to regulate synaptic activity and may also play a role in gene regulation via interaction with DNA in the cell nucleus. Here, we address the role of the negatively-charged C-terminus in the interaction between aS and DNA using single-molecule techniques. Using nanofluidic channels, we demonstrate that truncation of the C-terminus of aS induces differential effects on DNA depending on the extent of the truncation. The DNA extension increases for full-length aS and the (1–119)aS variant, but decreases about 25% upon binding to the (1–97)aS variant. Atomic force microscopy imaging showed full protein coverage of the DNA at high aS concentration. The characterization of biophysical properties of DNA when in complex with aS variants may provide important insights into the role of such interactions in PD, especially since C-terminal aS truncations have been found in clinical samples from PD patients.
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| 6. |
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| 7. |
- Jiang, Kai, 1988, et al.
(author)
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The HIV-1 nucleocapsid chaperone protein forms locally compacted globules on long double-stranded DNA
- 2021
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In: Nucleic Acids Research. - : Oxford University Press (OUP). - 0305-1048 .- 1362-4962. ; 49:8, s. 4550-4563
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Journal article (peer-reviewed)abstract
- The nucleocapsid (NC) protein plays key roles in Human Immunodeficiency Virus 1 (HIV-1) replication, notably by condensing and protecting the viral RNA genome and by chaperoning its reverse transcription into double-stranded DNA (dsDNA). Recent findings suggest that integration of viral dsDNA into the host genome, and hence productive infection, is linked to a small subpopulation of viral complexes where reverse transcription was completed within the intact capsid. Therefore, the synthesized dsDNA has to be tightly compacted, most likely by NC, to prevent breaking of the capsid in these complexes. To investigate NC's ability to compact viral dsDNA, we here characterize the compaction of single dsDNA molecules under unsaturated NC binding conditions using nanofluidic channels. Compaction is shown to result from accumulation of NC at one or few compaction sites, which leads to small dsDNA condensates. NC preferentially initiates compaction at flexible regions along the dsDNA, such as AT-rich regions and DNA ends. Upon further NC binding, these condensates develop into a globular state containing the whole dsDNA molecule. These findings support NC's role in viral dsDNA compaction within the mature HIV-1 capsid and suggest a possible scenario for the gradual dsDNA decondensation upon capsid uncoating and NC loss.
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| 8. |
- Schmitt, Andreas, et al.
(author)
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PrgB promotes aggregation, biofilm formation, and conjugation through DNA binding and compaction
- 2018
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In: Molecular Microbiology. - : Wiley. - 1365-2958 .- 0950-382X. ; 109:3, s. 291-305
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Journal article (peer-reviewed)abstract
- Gram-positive bacteria deploy type IV secretion systems (T4SSs) to facilitate horizontal gene transfer. The T4SSs of Gram-positive bacteria rely on surface adhesins as opposed to conjugative pili to facilitate mating. Enterococcus faecalis PrgB is a surface adhesin that promotes mating pair formation and robust biofilm development in an extracellular DNA (eDNA) dependent manner. Here, we report the structure of the adhesin domain of PrgB. The adhesin domain binds and compacts DNA in vitro. In vivo PrgB deleted of its adhesin domain does not support cellular aggregation, biofilm development and conjugative DNA transfer. PrgB also binds lipoteichoic acid (LTA), which competes with DNA binding. We propose that PrgB binding and compaction of eDNA facilitates cell aggregation and plays an important role in establishment of early biofilms in mono- or polyspecies settings. Within these biofilms, PrgB mediates formation and stabilization of direct cell-cell contacts through alternative binding of cell-bound LTA, which in turn promotes establishment of productive mating junctions and efficient intra- or inter-species T4SS-mediated gene transfer.
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| 9. |
- Song, Kai, 1988-, et al.
(author)
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Conservation genomics in the boreal forest : Population structure and local adaptation in the sibling species Chinese Grouse and Hazel Grouse
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Other publication (other academic/artistic)abstract
- The climate of the world’s arctic regions, including the poles and the Tibetan plateau region, act as a bellwether for global change. On the Tibetan plateau, there are numerous species well adapted to cold environments. The Chinese Grouse and Hazel Grouse are sibling species distributed in the Eurasian subarctic forests of the Tibetan plateau respectively. Conservation genomics are transforming our understanding of organismal responses in a changing Arctic boreal forest. In this study, we used 29 individuals from the sister species Chinese Grouse and Hazel Grouse from the boreal forest in Eurasia. Our results provide insights into the genetic diversity and differentiation in to different geographic populations of the two species. Full genome sequencing of samples covering the distribution area of grouse species throughout the Eurasian boreal forest has enabled us to provide the first analysis of the population structure and introgression. Through selective sweep analysis, we detected that the Chinese Grouse inhabiting the QTP high altitude environment show evidence of having evolved adaptations to hypobaric hypoxia and high ultraviolet radiation.
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| 10. |
- Song, Kai, 1988-, et al.
(author)
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Demographic history and divergence of sibling grouse species inferred from whole genome sequencing reveal past effects of climate change
- 2021
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In: BMC Ecology and Evolution. - : BioMed Central (BMC). - 2730-7182. ; 21:1
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Journal article (peer-reviewed)abstract
- Background The boreal forest is one of the largest biomes on earth, supporting thousands of species. The global climate fluctuations in the Quaternary, especially the ice ages, had a significant influence on the distribution of boreal forest, as well as the divergence and evolution of species inhabiting this biome. To understand the possible effects of on-going and future climate change it would be useful to reconstruct past population size changes and relate such to climatic events in the past. We sequenced the genomes of 32 individuals from two forest inhabiting bird species, Hazel Grouse (Tetrastes bonasia) and Chinese Grouse (T. sewerzowi) and three representatives of two outgroup species from Europe and China. Results We estimated the divergence time of Chinese Grouse and Hazel Grouse to 1.76 (0.46-3.37) MYA. The demographic history of different populations in these two sibling species was reconstructed, and showed that peaks and bottlenecks of effective population size occurred at different times for the two species. The northern Qilian population of Chinese Grouse became separated from the rest of the species residing in the south approximately 250,000 years ago and have since then showed consistently lower effective population size than the southern population. The Chinese Hazel Grouse population had a higher effective population size at the peak of the Last Glacial Period (approx. 300,000 years ago) than the European population. Both species have decreased recently and now have low effective population sizes. Conclusions Combined with the uplift history and reconstructed climate change during the Quaternary, our results support that cold-adapted grouse species diverged in response to changes in the distribution of palaeo-boreal forest and the formation of the Loess Plateau. The combined effects of climate change and an increased human pressure impose major threats to the survival and conservation of both species.
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