DNA aptamers have potential for disease diagnosis and as therapeutics, particularly when interfaced with programmable molecular technology. Here we have combined DNA aptamers specific for the malaria biomarker Plasmodium falciparum lactate dehydrogenase (PfLDH) with a DNA origami scaffold. Twelve aptamers that recognise PfLDH were integrated into a rectangular DNA origami and atomic force microscopy demonstrated that the incorporated aptamers preserve their ability to specifically bind target protein. Captured PfLDH retained enzymatic activity and protein-aptamer binding was observed dynamically using high-speed AFM. This work demonstrates the ability of DNA aptamers to recognise a malaria biomarker whilst being integrated within a supramolecular DNA scaffold, opening new possibilities for malaria diagnostic approaches based on DNA nanotechnology.

The Elongator complex catalyzes posttranscriptional tRNA modifications by attaching carboxy-methyl (cm⁵) moieties to uridine bases located in the wobble position. The catalytic subunit Elp3 is highly conserved and harbors two individual subdomains, a radical S-adenosyl methionine (rSAM) and a lysine acetyltransferase (KAT) domain. The details of its modification reaction cycle and particularly the substrate specificity of its KAT domain remain elusive. Here, we present the co-crystal structure of bacterial Elp3 (DmcElp3) bound to an acetyl-CoA analog and compare it to the structure of a monomeric archaeal Elp3 from Methanocaldococcus infernus (MinElp3). Furthermore, we identify crucial active site residues, confirm the importance of the extended N-terminus for substrate recognition and uncover the specific induction of acetyl-CoA hydrolysis by different tRNA species. In summary, our results establish the clinically relevant Elongator subunit as a non-canonical acetyltransferase and genuine tRNA modification enzyme.

TRNAs are short noncoding RNAs responsible for decoding mRNA codon triplets, delivering correct amino acids to the ribosome, and mediating polypeptide chain formation. Due to their key roles during translation, tRNAs have a highly conserved shape and large sets of tRNAs are present in all living organisms. Regardless of sequence variability, all tRNAs fold into a relatively rigid three-dimensional L-shaped structure. The conserved tertiary organization of canonical tRNA arises through the formation of two orthogonal helices, consisting of the acceptor and anticodon domains. Both elements fold independently to stabilize the overall structure of tRNAs through intramolecular interactions between the D- and T-arm. During tRNA maturation, different modifying enzymes posttranscriptionally attach chemical groups to specific nucleotides, which not only affect translation elongation rates but also restrict local folding processes and confer local flexibility when required. The characteristic structural features of tRNAs are also employed by various maturation factors and modification enzymes to assure the selection, recognition, and positioning of specific sites within the substrate tRNAs. The cellular functional repertoire of tRNAs continues to extend well beyond their role in translation, partly, due to the expanding pool of tRNA-derived fragments. Here, we aim to summarize the most recent developments in the field to understand how three-dimensional structure affects the canonical and noncanonical functions of tRNA.

The eukaryotic Elongator complex participates in modification of uridines in tRNAs. Structural and functional work on a bacterial Elp3, the catalytic subunit of Elongator, provides insight into the function and mechanism of this important enzyme. During translation elongation, decoding is based on the recognition of codons by corresponding tRNA anticodon triplets. Molecular mechanisms that regulate global protein synthesis via specific base modifications in tRNA anticodons are receiving increasing attention. The conserved eukaryotic Elongator complex specifically modifies uridines located in the wobble base position of tRNAs. Mutations in Elongator subunits are associated with certain neurodegenerative diseases and cancer. Here we present the crystal structure of D. mccartyi Elp3 (DmcElp3) at 2.15-Å resolution. Our results reveal an unexpected arrangement of Elp3 lysine acetyltransferase (KAT) and radical S-adenosyl methionine (SAM) domains, which share a large interface and form a composite active site and tRNA-binding pocket, with an iron–sulfur cluster located in the dimerization interface of two DmcElp3 molecules. Structure-guided mutagenesis studies of yeast Elp3 confirmed the relevance of our findings for eukaryotic Elp3s and should aid in understanding the cellular functions and pathophysiological roles of Elongator.

The spider silk spinning process converts spidroins from an aqueous form to a tough fiber. This spinning process has been investigated by numerous researchers, and micelles or liquid crystals of spidroins have been reported to form silk fibers, which are bundles of silk microfibrils. However, the formation process of silk microfibrils has not been clarified previously. Here, we report that silk microfibrils are generated through the formation, homogenization, and linkage of liquid crystalline granules without micelle-like structures. Heterogeneous granules on the submicron to micron scale were observed in the storage sac, whereas homogeneous granules with diameters of approximately 100 nm were aligned along the tapering duct. In the spun fibers, the homogeneous granules were connected along the fiber axis. This is the first clear description of the formation of granule-based microfibrils in the spinning process, which is the key conversion process leading to the unique hierarchical structure of spider dragline.