JRAB/MICAL-L2 undergoes liquid-liquid phase separation to form tubular recycling endosomes

Nano-Scale Video Imaging of Motility Machinery by High-Speed Atomic Force Microscopy

Motility is a vital aspect of many forms of life, with a wide range of highly conserved as well as highly unique systems adapted to the needs of various organisms and environments. While many motility systems are well studied using structural techniques like X-ray crystallography and electron microscopy, as well as fluorescence microscopy methodologies, it is difficult to directly determine the relationship between the shape and movement of a motility system due to a notable gap in spatiotemporal resolution. Bridging this gap as well as understanding the dynamic molecular movements that underpin motility mechanisms has been challenging. The advent of high-speed atomic force microscopy (HS-AFM) has provided a new window into understanding these nano-scale machines and the dynamic processes underlying motility. In this review, we highlight some of the advances in this field, ranging from reconstituted systems and purified higher-order supramolecular complexes to live cells, in both prokaryotic and eukaryotic contexts.

Single-cell infrared vibrational analysis by optical trapping mid-infrared photothermal microscopy

Single-cell analysis by means of vibrational spectroscopy combined with optical trapping is a reliable platform for unveiling cell-to-cell heterogeneities in vast populations. Although infrared (IR) vibrational spectroscopy provides rich molecular fingerprint information on biological samples in a label-free manner, its application with optical trapping has never been achieved due to weak gradient forces generated by the diffraction-limited focused IR beam and strong background of water absorption. Herein, we present single-cell IR vibrational analysis that incorporates mid-infrared photothermal (MIP) microscopy with optical trapping. Optically trapped single polymer particles and red blood cells (RBCs) in blood could be chemically identified owing to their IR vibrational fingerprints. This single-cell IR vibrational analysis further allowed us to probe the chemical heterogeneities of RBCs originating from the variation in the intracellular characteristics. Our demonstration paves the way for the IR vibrational analysis of single cells and chemical characterization in various fields.

Guide to studying intrinsically disordered proteins by high-speed atomic force microscopy

Intrinsically disordered proteins (IDPs) are partially or entirely disordered. Their intrinsically disordered regions (IDRs) dynamically explore a wide range of structural space by their highly flexible nature. Due to this distinct feature largely different from structured proteins, conventional structural analyses relying on ensemble averaging is unsuitable for characterizing the dynamic structure of IDPs. Therefore, single-molecule measurement tools have been desired in IDP studies. High-speed atomic force microscopy (HS-AFM) is a unique tool that allows us to directly visualize single biomolecules at 2-3 nm lateral and ∼ 0.1 nm vertical spatial resolution, and at sub-100 ms temporal resolution under near physiological conditions, without any chemical labeling. HS-AFM has been successfully used not only to characterize the shape and motion of IDP molecules but also to visualize their function-related dynamics. In this article, after reviewing the principle and current performances of HS-AFM, we describe experimental considerations in the HS-AFM imaging of IDPs and methods to quantify molecular features from captured images. Finally, we outline recent HS-AFM imaging studies of IDPs.