Rebecca Meyer

Orthogonal Protein Decoration of DNA Origami

Structural DNA nanotechnology 2] and the technique of DNA origami enable the rapid generation of a plethora of complex self-assembled nanostructures. Since DNA molecules themselves display limited chemical, optical, and electronic functionality, it is of utmost importance to devise methods to decorate DNA scaffolds with functional moieties to realize applications in sensing, catalysis, and device fabrication. Protein functionalization is particulary desirable because it allows exploitation of an almost unlimited variety of functional elements which nature has evolved over billions of years. The delicate architecture of proteins has resulted in no generally applicable method being currently available to selectively couple these components on DNA scaffolds, and thus approaches used so far are based on reversible antibody– antigen interactions, 9] aptamer binding, 11] nucleic acid hybridization of DNA-tagged proteins, 13] or predominantly biotin–streptavidin (STV) interactions. We demonstrate here that DNA nanostructures can be site-specifically decorated with several different proteins by using coupling systems orthogonal to the biotin–STV system. In particular, benzylguanine (BG) and chlorohexane (CH) groups incorporated in DNA origami have been used as suicide ligands for the site-specific coupling of fusion proteins containing the self-labeling protein tags O-alkylguanine-DNA-alkyltransferase (hAGT), which is often referred to as “Snap-tag”, or haloalkane dehalogenase, which is also known as “HaloTag”. By using various model proteins we demonstrate the general applicability of this approach for the generation of DNA superstructures that are selectively decorated with multiple different proteins. To realize orthogonal protein immobilization on DNA origami using self-ligating protein tags, we chose the Snap-tag, developed by Johnsson and co-workers, and the commercially available HaloTag system. The respective smallmolecule suicide tags (O-benzylguanine (BG) and 5-chlorohexane (CH)) for both self-labeling protein tags are readily available as amino-reactive N-hydroxysuccinimide (NHS) derivatives (BG-NHS and CH-NHS; Figure 1a). Complete derivatization of alkylamino-modified oligonucleotides was achieved by coupling with 30 molar equivalents of BG-NHS or CH-NHS, as indicated by electrophoretic analysis (Figure 1b). To gain access to fusion proteins bearing the complementary Snapand Halo-protein tags, we constructed expression plasmids by genetic fusion of the genes encoding the protein of interest (POI) and Snap-tag or HaloTag (see the Supporting Information). As model POIs we chose the fluorescent proteins enhanced yellow fluorescent protein (EYFP) and mKate, the enzymes cytochrome C peroxidase (CCP) and esterase 2 from Alicyclobacillus acidocaldarius thermos (EST2), to which the self-labeling tags were fused at the C terminus (POI-Snap or POI-Halo, respectively). In addition, the bispecific Halo-Snap fusion protein “covalin”, a chimera which specifically reacts with both BG and CH, as well as monovalent STV (mSTV), were used in this study. The fusion proteins were overexpressed and purified by conventional procedures (see the Supporting Information). The coupling of BGand CHmodified oligonucleotides to the protein was analyzed by using covalin as the initial model to simplify the electrophoretic characterization. It is shown in Figure 1c that both BGand CH-modified single-stranded DNA (ssDNA) oligonucleotides couple effectively to generate the corresponding DNA–covalin conjugates in nearly quantitative yields. DNA coupling of the aforementioned POI fusions, namely mKateSnap, EST2-SNAP, mKate-Halo, CCP-Halo, and EYFP-Halo occurred in a highly specific manner (Figure 1d), and neither Snap or Halo nor mSTV revealed cross-reactivity for the orthogonal-tagged DNA oligomers. We then used SARSE software to aid in the design of face-shaped DNA origami to demonstrate the selective immobilization of protein on DNA nanostructures. Correct folding of M13mp18 ssDNA through the use of 236 staple strands was analyzed by atomic force microscopy (AFM; details of the sequence design as well as experimental procedures are reported in the Supporting Information). Figure 2a illustrates that the face-shaped DNA origami was obtained in high purity, and high-resolution AFM clearly revealed the proposed ears, neck, and seam features of this structure. As an initial test for protein decoration, we selected 23 staple strands, which were biotinylated to create eyes (2 6 [*] Dr. B. Sacc , Dipl.-Chem. R. Meyer, Dipl.-Biotechnol. M. Erkelenz, M. Sc. K. Kiko, A. Arndt, Dr. H. Schroeder, Dr. K. S. Rabe, Prof. C. M. Niemeyer Technische Universit t Dortmund, Fakult t Chemie Biologisch-Chemische Mikrostrukturtechnik Otto-Hahn Strasse 6, 44227 Dortmund (Germany) Fax: (+ 49)231-755-7082 E-mail: christof.niemeyer@tu-dortmund.de [] These authors contributed equally to this work.

Advances in DNA-directed immobilization

DNA-directed immobilization (DDI) of proteins is a chemically mild and highly efficient method for generating (micro)structured patterns of proteins on surfaces. Twenty years after its initial description, the DDI method has proven its robustness and versatility in numerous applications, ranging from biosensing and biomedical diagnostics, to fundamental studies in biology and medicine on the single-cell level. This review gives a brief summary on technical aspects of the DDI method and illustrates its scope for applications with an emphasis on studies in cell biology.

Orthogonal Protein Decoration of DNA Nanostructures

The development of robust DNA-protein coupling techniques is mandatory for applications of DNA nanostructures in biomedical diagnostics, fundamental biochemistry, and other fields in biomolecular nanosciences. The use of self-labeling fusion proteins, which are orthogonal to biotin-streptavidin and antibody-antigen interactions, is described for the site-selective protein decoration of two exemplary DNA nanostructures: a four-way junction X-tile motif and a 3D DNA tetrahedron. Multifunctional DNA superstructures bearing up to four different proteins are generated and characterized by electrophoresis and microplate-based functionality assays. Steric and electrostatic interactions are identified as critical parameters controlling the efficiency of DNA-protein ligation. The results indicate that this method is versatile and broadly applicable, not only for the functionalization of DNA architectures but also for the site-specific decoration of other molecular materials and devices containing several different proteins.

Multiscale Origami Structures as Interface for Cells.

A DNA-based platform was developed to address fundamental aspects of early stages of cell signaling in living cells. By site-directed sorting of differently encoded, protein-decorated DNA origami structures on DNA microarrays, we combine the advantages of the bottom-up self-assembly of protein-DNA nanostructures and top-down micropatterning of solid surfaces to create multiscale origami structures as interface for cells (MOSAIC). In a proof-of-principle, we use this technology to analyze the activation of epidermal growth factor (EGF) receptors in living MCF7 cells using DNA origami structures decorated on their surface with distinctive nanoscale arrangements of EGF ligand entities. MOSAIC holds the potential to present to adhered cells well-defined arrangements of ligands with full control over their number, stoichiometry, and precise nanoscale orientation. It therefore promises novel applications in the life sciences, which cannot be tackled by conventional technologies.

A Facile Method for Preparation of Tailored Scaffolds for DNA-Origami

A convenient PCR cloning strategy allows one to prepare hundreds of picomoles of circular single-stranded DNA molecules, which are suitable as scaffolds for the assembly of DNA origami structures. The method is based on a combination of site-directed mutagenesis and site- and ligation-independent cloning protocols, with simultaneous insertion of a nicking endonuclease restriction site on a double-stranded plasmid of desired length and sequence.

Reversible Reconfiguration of DNA Origami Nanochambers Monitored by Single‐Molecule FRET

Today, DNA nanotechnology is one of the methods of choice to achieve spatiotemporal control of matter at the nanoscale. By combining the peculiar spatial addressability of DNA origami structures with the switchable mechanical movement of small DNA motifs, we constructed reconfigurable DNA nanochambers as dynamic compartmentalization systems. The reversible extension and contraction of the inner cavity of the structures was used to control the distance-dependent energy transfer between two preloaded fluorophores. Interestingly, single-molecule FRET studies revealed that the kinetics of the process are strongly affected by the choice of the switchable motifs and/or actuator sequences, thus offering a valid method for fine-tuning the dynamic properties of large DNA nanostructures. We envisage that the proposed DNA nanochambers may function as model structures for artificial biomimetic compartments and transport systems.

Multi-color polymer pen lithography for oligonucleotide arrays

Multi-color patterning by polymer pen lithography (PPL) was used to fabricate covalently immobilized fluorophore and oligonucleotide arrays with up to five different components. The oligonucleotide arrays offer a virtually unlimited inventory of orthogonal binding tags for self-assembly of proteins as demonstrated by use of the arrays to monitor cell-protein interactions of MCF7 cells.

A Rationally Designed Connector for Assembly of Protein‐Functionalized DNA Nanostructures

We report on the rational engineering of the binding interface of the self‐ligating HaloTag protein to generate an optimized linker for DNA nanostructures. Five amino acids positioned around the active‐site entry channel for the chlorohexyl ligand (CH) of the HaloTag protein were exchanged for positively charged lysine amino acids to produce the HOB (halo‐based oligonucleotide binder) protein. HOB was genetically fused with the enzyme cytochrome P450 BM3, as well as with BMR, the separated reductase domain of BM3. The resulting HOB‐fusion proteins revealed significantly improved rates in ligation with CH‐modified oligonucleotides and DNA origami nanostructures. These results suggest that the efficient self‐assembly of protein‐decorated DNA structures can be greatly improved by fine‐tuning of the electrostatic interactions between proteins and the negatively charged nucleic acid nanostructures.

DNA-Directed Assembly of Capture Tools for Constitutional Studies of Large Protein Complexes

Large supramolecular protein complexes, such as the molecular machinery involved in gene regulation, cell signaling, or cell division, are key in all fundamental processes of life. Detailed elucidation of structure and dynamics of such complexes can be achieved by reverse-engineering parts of the complexes in order to probe their interactions with distinctive binding partners in vitro. The exploitation of DNA nanostructures to mimic partially assembled supramolecular protein complexes in which the presence and state of two or more proteins are decisive for binding of additional building blocks is reported here. To this end, four-way DNA Holliday junction motifs bearing a fluorescein and a biotin tag, for tracking and affinity capture, respectively, are site-specifically functionalized with centromeric protein (CENP) C and CENP-T. The latter serves as baits for binding of the so-called KMN component, thereby mimicking early stages of the assembly of kinetochores, structures that mediate and control the attachment of microtubules to chromosomes in the spindle apparatus. Results from pull-down experiments are consistent with the hypothesis that CENP-C and CENP-T may bind cooperatively to the KMN network.

Site-Directed, On-Surface Assembly of DNA Nanostructures

Two-dimensional DNA lattices have been assembled from DNA double-crossover (DX) motifs on DNA-encoded surfaces in a site-specific manner. The lattices contained two types of single-stranded protruding arms pointing into opposite directions of the plane. One type of these protruding arms served to anchor the DNA lattice on the solid support through specific hybridization with surface-bound, complementary capture oligomers. The other type of arms allowed for further attachment of DNA-tethered probe molecules on the opposite side of the lattices exposed to the solution. Site-specific lattice assembly and attachment of fluorophore-labeled oligonucleotides and DNA-protein conjugates was demonstrated using DNA microarrays on flat, transparent mica substrates. Owing to their programmable orientation and addressability over a broad dynamic range from the nanometer to the millimeter length scale, such supramolecular architecture might be used for presenting biomolecules on surfaces, for instance, in biosensor applications.