Two GPSes in a Ball: Deciphering the Endosomal Tug-of-War Using Plasmonic Dark-Field STORM

Digitally Assisted Single-Particle Tracking for Accurate Analysis of Complicated Cargo Transport Dynamics in Microtubule Networks

Intracellular transport is a fundamental process crucial for cellular function, driven by the coordinated action of motor proteins that move cargo along microtubule tracks. Traditional tracking methods primarily focus on cargo trajectories, often overlooking rotational dynamics and their impact on cargo interactions with the complex microtubule network. To address this limitation, we introduced a digitally assisted single-particle tracking (dSPT) method that significantly advances the angular resolution of intracellular cargo dynamics. By integrating intensity measurements with advanced digital classification algorithms to process defocused half-plane image patterns captured through bifocal parallax microscopy, this approach extends the angular resolution range from the conventional method to a full 0-360° range, even in heterogeneous cellular environments, while maintaining high spatial and temporal resolutions. In intracellular transport events, we directly observed the accurate determination of the chiral rotational directions and precise calculation of the step angles. When combined with super-resolution radial fluctuation (SRRF) imaging to achieve higher-resolution microtubule imaging, our dSPT technique enables in vivo investigations of cargo dynamics during intracellular transport. To validate this, we studied the rotational dynamics of the cargo in microtubule confinement. Furthermore, we identified characteristic patch-searching patterns in the microtubule network, where cargo exhibited a combined motion pattern of confined and hopping diffusion to navigate through the constraints imposed by the microtubules.

Modular and Nondisturbing Chimeric Adaptor Protein for Surface Chemistry of Small Extracellular Vesicles

Current chemical strategies for modifying the surface of extracellular vesicles (sEVs) often struggle to balance efficient functionalization with preserving structural integrity. Here, we present a modular approach for the surface modification of sEVs using a chimeric adaptor protein (CAP). The CAP was designed with three key features: a SNAP-tag for stable and modular binding, long and rigid linker to enhance spatial accessibility and conjugation efficiency, and the N-terminal sorting domain derived from syntenin to improve CAP expression on the sEV. We established a postsynthetic method to introduce diverse functional molecules onto sEVs, creating a versatile system termed "sEV-X" (where X represents an organic molecule, protein, or nanoparticle). Quantitative analyses at the single-molecule level revealed a linear relationship between CAP expression and the number of conjugated functional molecules, underscoring the importance of steric hindrance mitigation in sEV surface engineering. Moreover, antibody-conjugated sEVs as drug carriers, demonstrated significant tumor-specific delivery and therapeutic efficacy in a tumor-bearing mouse model, underscoring the potential of CAP-expressing sEVs as a customizable therapeutic vesicle. Overall, the CAP technology may serve as a universal platform for advancing the development of sEV-based therapeutics.

Temporal Patterns of Angular Displacement of Endosomes: Insights into Motor Protein Exchange Dynamics

The material transport system, facilitated by motor proteins, plays a vital role in maintaining a non-equilibrium cellular state. However, understanding the temporal coordination of motor protein activity requires an advanced imaging technique capable of measuring 3D angular displacement in real-time. In this study, a Fourier transform-based plasmonic dark-field microscope has been developed using anisotropic nanoparticles, enabling the prolonged and simultaneous observation of endosomal lateral and rotational motion. A sequence of discontinuous 3D angular displacements has been observed during the pause and run phases of transport. Notably, a serially correlated temporal pattern in the intermittent rotational events has been demonstrated during the tug-of-war mechanism, indicating Markovian switching between the exploitational and explorational modes of motor protein exchange prior to resuming movement. Alterations in transition frequency and the exploitation-to-exploration ratio upon dynein inhibitor treatment highlight the relationship between disrupted motor coordination and reduced endosomal transport efficiency. Collectively, these results suggest the importance of orchestrated temporal motor protein patterns for efficient cellular transport.

Single-Molecule Imaging of Membrane Proteins on Vascular Endothelial Cells

Transporting substances such as gases, nutrients, waste, and cells is the primary function of blood vessels. Vascular cells use membrane proteins to perform crucial endothelial functions, including molecular transport, immune cell infiltration, and angiogenesis. A thorough understanding of these membrane receptors from a clinical perspective is warranted to gain insights into the pathogenesis of vascular diseases and to develop effective methods for drug delivery through the vascular endothelium. This review summarizes state-of-the-art single-molecule imaging techniques, such as super-resolution microscopy, single-molecule tracking, and protein-protein interaction analysis, for observing and studying membrane proteins. Furthermore, recent single-molecule studies of membrane proteins such as cadherins, integrins, caveolins, transferrin receptors, vesicle-associated protein-1, and vascular endothelial growth factor receptor are discussed.