| 1. |
- Bosaeus, Niklas, 1982, et al.
(författare)
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Force-induced melting of DNA-evidence for peeling and internal melting from force spectra on short synthetic duplex sequences
- 2014
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Ingår i: Nucleic Acids Research. - : Oxford University Press (OUP). - 0305-1048 .- 1362-4962. ; 42:12, s. 8083-8091
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Tidskriftsartikel (refereegranskat)abstract
- Overstretching of DNA occurs at about 60-70 pN when a torsionally unconstrained double-stranded DNA molecule is stretched by its ends. During the transition, the contour length increases by up to 70% without complete strand dissociation. Three mechanisms are thought to be involved: force-induced melting into single-stranded DNA where either one or both strands carry the tension, or a B-to-S transition into a longer, still base-paired conformation. We stretch sequence-designed oligonucleotides in an effort to isolate the three processes, focusing on force-induced melting. By introducing site-specific inter-strand cross-links in one or both ends of a 64 bp AT-rich duplex we could repeatedly follow the two melting processes at 5 mM and 1 M monovalent salt. We find that when one end is sealed the AT-rich sequence undergoes peeling exhibiting hysteresis at low and high salt. When both ends are sealed the AT sequence instead undergoes internal melting. Thirdly, the peeling melting is studied in a composite oligonucleotide where the same AT-rich sequence is concatenated to a GC-rich sequence known to undergo a B-to-S transition rather than melting. The construct then first melts in the AT-rich part followed at higher forces by a B-to-S transition in the GC-part, indicating that DNA overstretching modes are additive.
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| 2. |
- Bosaeus, Niklas, 1982, et al.
(författare)
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Tension induces a base-paired overstretched DNA conformation
- 2012
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 109:38, s. 15179-15184
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Tidskriftsartikel (refereegranskat)abstract
- Mixed-sequence DNA molecules undergo mechanical overstretching by approximately 70% at 60-70 pN. Since its initial discovery 15 y ago, a debate has arisen as to whether the molecule adopts a new form [Cluzel P, et al. (1996) Science 271: 792-794; Smith SB, Cui Y, Bustamante C (1996) Science 271: 795-799], or simply denatures under tension [van Mameren J, et al. (2009) Proc Natl Acad Sci USA 106: 18231-18236]. Here, we resolve this controversy by using optical tweezers to extend small 60-64 bp single DNA duplex molecules whose base content can be designed at will. We show that when AT content is high (70%), a force-induced denaturation of the DNA helix ensues at 62 pN that is accompanied by an extension of the molecule of approximately 70%. By contrast, GC-rich sequences (60% GC) are found to undergo a reversible overstretching transition into a distinct form that is characterized by a 51% extension and that remains base-paired. For the first time, results proving the existence of a stretched basepaired form of DNA can be presented. The extension observed in the reversible transition coincides with that produced on DNA by binding of bacterial RecA and human Rad51, pointing to its possible relevance in homologous recombination.
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| 3. |
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| 4. |
- Börjesson, Karl, 1982, et al.
(författare)
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Functionalized Nanostructures: Redox-Active Porphyrin Anchors for Supramolecular DNA Assemblies
- 2010
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 4:9, s. 5037-5046
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Tidskriftsartikel (refereegranskat)abstract
- We have synthesized and studied a supramolecular system comprising a 39-mer DNA with porphyrin-modified thymidine nucleosides anchored to the surface of large unilamellar vesicles (liposomes). Liposome porphyrin binding characteristics, such as orientation, strength, homogeneity, and binding site size, was determined, suggesting that the porphyrin is well suited as a photophysical and redox-active lipid anchor, in comparison to the inert cholesterol anchor commonly used today. Furthermore, the binding characteristics and hybridization capabilities were studied as a function of anchor size and number of anchoring points, properties that are of importance for our future plans to use the addressability of these redox-active nodes in larger DNA-based nanoconstructs. Electron transfer from photoexcited porphyrin to a lipophilic benzoquinone residing in the lipid membrane was characterized by steady-state and time-resolved fluorescence and verified by femtosecond transient absorption.
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| 5. |
- Hannestad, Jonas, 1981, et al.
(författare)
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Kinetics of Diffusion-Mediated DNA Hybridization in Lipid Monolayer Films Determined by Single-Molecule Fluorescence Spectroscopy
- 2013
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Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-086X .- 1936-0851. ; 7:1, s. 308-315
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Tidskriftsartikel (refereegranskat)abstract
- We use single-molecule fluorescence microscopy to monitor individual hybridization reactions between membrane-anchored DNA strands, occurring in nanofluidic lipid monolayer films deposited on Teflon AF substrates. The DNA molecules are labeled with different fluorescent dyes, which make it possible to simultaneously monitor the movements of two different molecular species, thus enabling tracking of both reactants and products. We employ lattice diffusion simulations to determine reaction probabilities upon interaction. The observed hybridization rate of the 40-mer DNA was more than 2-fold higher than that of the 20-mer DNA. Since the lateral diffusion coefficient of the two different constructs is nearly identical, the effective molecule radius determines the overall kinetics. This implies that when two DNA molecules approach each other, hydrogen bonding takes place distal from the place where the DNA is anchored to the surface. Strand closure then propagates bidirectionally through a zipper-like mechanism, eventually bringing the lipid anchors together. Comparison with hybridization rates for corresponding DNA sequences in solution reveals that hybridization rates are lower for the lipid-anchored strands and that the dependence on strand length is stronger.
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| 6. |
- Lundberg, Erik, 1981, et al.
(författare)
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A new fixation strategy for addressable nano-network building blocks
- 2010
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Ingår i: Chemical Communications. - 1364-548X .- 1359-7345. ; 46:21, s. 3714-3716
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Tidskriftsartikel (refereegranskat)abstract
- Rapid controlled self-assembly makes DNA ideal for building nanostructures. A problem using hybridized intermediates in hierarchic assembly is their thermodynamic lability. We demonstrate a click-fixation technology by which robust hexagonal DNA modules can be made. This principle is applicable to a wide variety of DNA nanoconstructs.
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