Artificial protein assemblies with well-defined supramolecular protein nanostructures.

Nature uses a wide range of well-defined biomolecular assemblies in diverse cellular processes, where proteins are major building blocks for these supramolecular assemblies. Inspired by their natural counterparts, artificial protein-based assemblies have attracted strong interest as new bio-nanostructures, and strategies to construct ordered protein assemblies have been rapidly expanding. In this review, we provide an overview of very recent studies in the field of artificial protein assemblies, with the particular aim of introducing major assembly methods and unique features of these assemblies. Computational de novo designs were used to build various assemblies with artificial protein building blocks, which are unrelated to natural proteins. Small chemical ligands and metal ions have also been extensively used for strong and bio-orthogonal protein linking. Here, in addition to protein assemblies with well-defined sizes, protein oligomeric and array structures with rather undefined sizes (but with definite repeat protein assembly units) also will be discussed in the context of well-defined protein nanostructures. Lastly, we will introduce multiple examples showing how protein assemblies can be effectively used in various fields such as therapeutics and vaccine development. We believe that structures and functions of artificial protein assemblies will be continuously evolved, particularly according to specific application goals.

Multivalent-Interaction-Driven Assembly of Discrete, Flexible, and Asymmetric Supramolecular Protein Nano-Prisms.

Current approaches to design monodisperse protein assemblies require rigid, tight, and symmetric interactions between oligomeric protein units. Herein, we introduce a new multivalent-interaction-driven assembly strategy that allows flexible, spaced, and asymmetric assembly between protein oligomers. We discovered that two polygonal protein oligomers (ranging from triangle to hexagon) dominantly form a discrete and stable two-layered protein prism nanostructure via multivalent interactions between fused binding pairs. We demonstrated that protein nano-prisms with long flexible peptide linkers (over 80 amino acids) between protein oligomer layers could be discretely formed. Oligomers with different structures could also be monodispersely assembled into two-layered but asymmetric protein nano-prisms. Furthermore, producing higher-order architectures with multiple oligomer layers, for example, 3-layered nano-prisms or nanotubes, was also feasible.

Recognition and Unfolding of c-MYC and Telomeric G-Quadruplex DNAs by the RecQ C-Terminal Domain of Human Bloom Syndrome Helicase.

G-quadruplex (G4) is a noncanonical DNA secondary structure formed by Hoogsteen base pairing. It is recognized by various DNA helicases involved in DNA metabolism processes such as replication and transcription. Human Bloom syndrome protein (BLM), one of five human RecQ helicases, is a G4 helicase. While several studies revealed the mechanism of G4 binding and unfolding by the conserved RecQ C-terminal (RQC) domain of BLM, how RQC recognizes different G4 topologies is still unclear. Here, we investigated the interaction of Myc-22(14/23T) G4 from the c-Myc promoter and hTelo G4 from the telomeric sequence with RQC. Myc-22(14/23T) and hTelo form parallel and (3+1) hybrid topologies, respectively. Our circular dichroism (CD) spectroscopy data indicate that RQC can partially unfold the parallel G4, even with a short 3' overhang, while it can only partially unfold the (3+1) hybrid G4 with a 3' overhang of 6 nucleotides or longer. We found that the intrinsic thermal stability of G4 does not determine RQC-induced G4 unfolding by comparing T m of G4s. We also showed that both parallel and (3+1) hybrid G4s bind to the ß-wing region of RQC. Thermodynamic analysis using isothermal titration calorimetry (ITC) showed that all interactions were endothermic and entropically driven. We suggest that RQC partially unfolds the parallel G4 more efficiently than the (3+1) hybrid G4 and binds to various G4 structures using its ß-wing region. By this information, our research provides new insights into the influence of G4 structure on DNA metabolic processes involving BLM.