Achieving spatiotemporal control of molecular self-assembly associated with actuation of biological functions inside living cells remains a challenge owing to the complexity of the cellular environments and the lack of characterization tools. We present, for the first time, the organelle-localized self-assembly of a peptide amphiphile as a powerful strategy for controlling cellular fate. A phenylalanine dipeptide (FF) with a mitochondria-targeting moiety, triphenyl phosphonium (Mito-FF), preferentially accumulates inside mitochondria and reaches the critical aggregation concentration to form a fibrous nanostructure, which is monitored by confocal laser scanning microscopy and transmission electron microscopy. The Mito-FF fibrils induce mitochondrial dysfunction via membrane disruption to cause apoptosis. The organelle-specific supramolecular system provides a new opportunity for therapeutics and in-depth investigations of cellular functions.
The digestion of pathogens inside phagosomes by immune cells occurs through asequence of reactions including acidification and proteolysis,b ut howt he reactions are orchestrated in the right order is unclear due to al acko f methods to simultaneously measure more than one reaction in phagosomes.H ere we report ab ifunctional Janus-particle probe to simultaneously monitor acidification and proteolysis in single phagosomes in live cells.Eachprobe consists of apH reporter and aproteolysis reporter that are spatially separated but function concurrently.U sing the Janus probes,w ef ound the acidic pH needed to initiate and maintain proteolysis, revealing the mechanism for the sequential occurrence of both reactions during pathogen digestion. We showed howb acterium-derived lipopolysaccharides alter the acidification and proteolysis in phagosomes.T his study showcases Janusparticle probes as ag enerally applicable tool for monitoring multiple reactions in intracellular vesicles.
Anisotropic mass diffusion in liquid crystals (LCs) is important from the point of both basic LC physics and their applications in optoelectronic devices. We use super-resolution fluorescence microscopy with astigmatic imaging to track 3D diffusion of quantum dots (QDs) in an ordered nematic LC. The method allowed us to evaluate the diffusion coefficients independently along the three spatial axes as well as to determine the absolute position of the QD with respect to the cell wall. We found variations of the diffusion coefficient along the different directions across the cell thickness and explained these as being due to changes of a tilt angle of the LC director. Close to the surface, the diffusion is slowed down due to the confinement effect of the cell wall. Overall, the QD diffusion is much slower than expected for a corresponding particle size. This phenomenon is suggested to originate from reorientation of the LC director in the vicinity of the particle.
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