Cell entry of anionic
nano-objects has been observed in various
types of viruses and self-assembled DNA nanostructures. Nevertheless,
the physical mechanism underlying the internalization of these anionic
particles across the negatively charged cell membrane remains poorly
understood. Here, we report the use of virus-mimicking designer DNA
nanostructures with near-atomic resolution to program “like-charge
attraction” at the interface of cytoplasmic membranes. Single-particle
tracking shows that cellular internalization of tetrahedral DNA nanostructures
(TDNs) depends primarily on the lipid-raft-mediated pathway, where
caveolin plays a key role in providing the short-range attraction
at the membrane interface. Both simulation and experimental data establish
that TDNs approach the membrane primarily with their corners to minimize
electrostatic repulsion, and that they induce uneven charge redistribution
in the membrane under the short-distance confinement by caveolin.
We expect that the nanoscale like-charge attraction mechanism provides
new clues for viral entry and general rules for rational design of
anionic carriers for therapeutics.
Quantum key distribution (QKD) 1,2 provides the only intrinsically unconditional secure method for communication based on principle of quantum mechanics. Compared with fiber-based demonstrations 3-5 , free-space links could provide the most appealing solution for much larger distance. Despite of significant efforts 6-13 , so far all realizations rely on stationary sites. Justifications are therefore extremely crucial for applications via a typical Low Earth Orbit Satellite (LEOS). To achieve direct and full-scale verifications, we demonstrate here three independent experiments with a decoy-state QKD system overcoming all the demanding conditions. The system is operated in a moving platform through a turntable, a floating platform through a hot-air balloon, and a huge loss channel, respectively, for substantiating performances under rapid motion, attitude change, vibration, random movement of satellites and in high-loss regime. The experiments cover expanded ranges for all the leading parameters of LEOS. Our results pave the way towards ground-satellite QKD and global quantum communication network.
Direct cellular imaging of the localization and dynamics of biomolecules helps to understand their function and reveals novel mechanisms at the single-cell resolution. In contrast to routine fluorescent-protein-based protein imaging, technology for RNA imaging remains less well explored because of the lack of enabling technology. Herein, we report the development of an aptamer-initiated fluorescence complementation (AiFC) method for RNA imaging by engineering a green fluorescence protein (GFP)-mimicking turn-on RNA aptamer, Broccoli, into two split fragments that could tandemly bind to target mRNA. When genetically encoded in cells, endogenous mRNA molecules recruited Split-Broccoli and brought the two fragments into spatial proximity, which formed a fluorophore-binding site in situ and turned on fluorescence. Significantly, we demonstrated the use of AiFC for high-contrast and real-time imaging of endogenous RNA molecules in living mammalian cells. We envision wide application and practical utility of this enabling technology to in vivo single-cell visualization and mechanistic analysis of macromolecular interactions.
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