ABSTRACT
The combination of lyotropic liquid crystals (LLCs) and low-molecular-weight gelators (LMWGs) for the formation of lyotropic liquid crystal gels (LLC gels) leads to a versatile and complex material combining properties of both parent systems. We gelled the calamitic nematic NC phases of a binary and ternary system using the LMWG 3,5-bis-(5-hexylcarbamoyl-pentoxy)-benzoic acid hexyl ester (BHPB-6). This binary system consists of the surfactant N,N-dimethyl-N-ethyl-1-hexadecylammonium bromide (CDEAB) and water, whereas the ternary system consists of the surfactant N,N,N-trimethyl-N-tetradecylammonium bromide (C14TAB), the cosurfactant n-decanol, and water. Though containing similar surfactants, the gelled NC phases of the binary and ternary systems show differences in their visual and gel properties. The gelled NC phase of the binary system remains clear for several days after preparation, whereas the gelled NC phase of the ternary system turns turbid within 24 h. We investigated the time evolution of the gel strength with oscillation rheology measurements (a) within the first 24 h and (b) up to two weeks after gel formation. The shape of the fibers was investigated over different time scales with freeze fracture electron microscopy (FFEM). We demonstrate that despite their similarities, the two LLC gels also have distinct differences.
ABSTRACT
The development of synthetic riboswitches has always been a challenge. Although a number of interesting proof-of-concept studies have been published, almost all of these were performed with the theophylline aptamer. There is no shortage of small molecule-binding aptamers; however, only a small fraction of them are suitable for RNA engineering since a classical SELEX protocol selects only for high-affinity binding but not for conformational switching. We now implemented RNA Capture-SELEX in our riboswitch developmental pipeline to integrate the required selection for high-affinity binding with the equally necessary RNA conformational switching. Thus, we successfully developed a new paromomycin-binding synthetic riboswitch. It binds paromomycin with a KD of 20 nM and can discriminate between closely related molecules both in vitro and in vivo. A detailed structure-function analysis confirmed the predicted secondary structure and identified nucleotides involved in ligand binding. The riboswitch was further engineered in combination with the neomycin riboswitch for the assembly of an orthogonal Boolean NOR logic gate. In sum, our work not only broadens the spectrum of existing RNA regulators, but also signifies a breakthrough in riboswitch development, as the effort required for the design of sensor domains for RNA-based devices will in many cases be much reduced.
