Vaccine efficacy can be increased by arraying immunogens in multivalent form on virus-like nanoparticles to enhance B cell activation. However, the effects of antigen copy number, spacing, and affinity, as well as the dimensionality and rigidity of scaffold presentation on B cell activation remain poorly understood. Here, we displayed the clinical vaccine immunogen eOD-GT8, an engineered outer domain of the HIV-1 glycoprotein-120, on DNA origami nanoparticles to systematically interrogate the impact of these nanoscale parameters on B cell activation in vitro. We found that B cell signalling is maximized by as few as five antigens maximally spaced on the surface of a 40 nm viral-like nanoparticle. Increasing antigen spacing up to ~25–30 nm monotonically increases B cell receptor activation. Moreover, scaffold rigidity is essential for robust B cell triggering. These results reveal molecular vaccine design principles that may be used to drive functional B cell responses.

DNA can be used to fabricate any free-form 2D drawing at the nanometer scale.

The T-cell lymphoma invasion and metastasis gene 1 (Tiam1) is a guanine exchange factor (GEF) for the Rho-family GTPase Rac1 that is crucial for the integrity of adherens junctions, tight junctions, and cell-matrix interactions. This GEF contains several protein-protein interaction domains, including a PDZ domain. Earlier studies identified a consensus PDZ-binding motif and a synthetic peptide capable of binding to the Tiam1 PDZ domain, but little is known about its ligand specificity and physiological role in cells. Here, we investigated the structure, specificity, and function of the Tiam1 PDZ domain. We determined the crystal structures of the Tiam1 PDZ domain free and in complex with a “model” peptide, which revealed the structural basis for ligand specificity. Protein database searches using the consensus PDZ-binding motif identified two eukaryotic cell adhesion proteins, Syndecan1 and Caspr4, as potential Tiam1 PDZ domain binding proteins. Equilibrium binding experiments confirmed that C-terminal peptides derived from Syndecan1 and Caspr4 bound the Tiam1 PDZ domain. NMR chemical shift perturbation experiments indicated that the Tiam1 PDZ/Syndecan1 and PDZ/Caspr4 complexes were structurally distinct and identified key residues likely to be responsible for ligand selectivity. Moreover, cell biological analysis established that Syndecan1 is a physiological binding partner of Tiam1 and that the PDZ domain has a function in cell-matrix adhesion and cell migration. Collectively, our data provide insight into the structure, specificity, and function of the Tiam1 PDZ domain. Importantly, our data report on a physiological role for the Tiam1 PDZ domain and establish a novel link between two previously unrelated signal transduction pathways, both of which are implicated in cancer.

3D polyhedral wireframe DNA nanoparticles (DNA-NPs) fabricated using scaffolded DNA origami offer complete and independent control over NP size, structure, and asymmetric functionalization on the 10–100 nm scale. However, the complex DNA sequence design needed for the synthesis of these versatile DNA-NPs has limited their widespread use to date. While the automated sequence design algorithms DAEDALUS and vHelix-BSCOR apply to DNA-NPs synthesized using either uniformly dual or hybrid single-dual duplex edges, respectively, these DNA-NPs are relatively compliant mechanically and are therefore of limited utility for some applications. Further, these algorithms are incapable of handling DNA-NP edge designs composed of more than two duplexes, which are needed to enhance DNA-NP mechanical stiffness. As an alternative, here we introduce the scaffolded DNA origami sequence design algorithm TALOS, which is a generalized procedure for the fully automated design of wireframe 3D polyhedra composed of edges of any cross section with an even number of duplexes, and apply it to DNA-NPs composed uniformly of single honeycomb edges. We also introduce a multiway vertex design that enables the fabrication of DNA-NPs with arbitrary edge lengths and vertex angles and apply it to synthesize a highly asymmetric origami object. Sequence designs are demonstrated to fold robustly into target DNA-NP shapes with high folding efficiency and structural fidelity that is verified using single particle cryo-electron microscopy and 3D reconstruction. In order to test its generality, we apply TALOS to design an in silico library of over 200 DNA-NPs of distinct symmetries and sizes, and for broad impact, we also provide the software as open source for the generation of custom NP designs.

Single-stranded DNA (ssDNA) increases the likelihood of homology directed repair with reduced cellular toxicity. However, ssDNA synthesis strategies are limited by the maximum length attainable, ranging from a few hundred nucleotides for chemical synthesis to a few thousand nucleotides for enzymatic synthesis, as well as limited control over nucleotide composition. Here, we apply purely enzymatic synthesis to generate ssDNA greater than 15 kilobases (kb) using asymmetric PCR, and illustrate the incorporation of diverse modified nucleotides for therapeutic and theranostic applications.

DNA is an ultra-high-density storage medium that could meet exponentially growing worldwide demand for archival data storage if DNA synthesis costs declined sufficiently and random access of files within exabyte-to-yottabyte-scale DNA data pools were feasible. To overcome the second barrier, here we encapsulate data-encoding DNA file sequences within impervious silica capsules that are surface-labeled with single-stranded DNA barcodes. Barcodes are chosen to represent file metadata, enabling efficient and direct selection of sets of files with Boolean logic. We demonstrate random access of image files from an image database using fluorescence sorting with selection sensitivity of 1 in 10 6 files, which thereby enables 1 in 10 6N per N optical channels. Our strategy thereby offers retrieval of random file subsets from exabyte and larger-scale long-term DNA file storage databases, offering a scalable solution for random-access of archival files in massive molecular datasets.

The GEF Tiam1 acts as a novel molecular link to the VE-cadherin–p67phox–Par3 polarity complex, leading to localized activation of Rac1 and NADPH oxidase in response to fluid flow.

SUMMARY PDZ (PSD-95/Dlg/ZO-1) domains are protein-protein interaction modules often regulated by ligand phosphorylation. Here, we investigated the specificity, structure, and dynamics of Tiam1 PDZ domain/ligand interactions. We show that the PDZ domain specifically binds syndecan1 (SDC1), phosphorylated SDC1 (pSDC1), and SDC3 but not other syndecan isoforms. The crystal structure of the PDZ/SDC1 complex indicates that syndecan affinity is derived from amino acids beyond the four C-terminal residues. Remarkably, the crystal structure of the PDZ/pSDC1 complex reveals a binding pocket that accommodates the phosphoryl group. Methyl relaxation experiments of PDZ/SCD1 and PDZ/pSDC1 complexes reveal that PDZ-phosphoryl interactions dampen dynamic motions in a distal region of the PDZ domain by decoupling them from the ligand-binding site. Our data are consistent with a selection model by which specificity and phosphorylation regulate PDZ/syndecan interactions and signaling events. Importantly, our relaxation data demonstrate that PDZ/phospho-ligand interactions regulate protein dynamics and their coupling to distal sites.