Acidic pH of Early Endosomes Governs SARS-CoV-2 Transport in Host Cells.

Endocytosis is a prominent mechanism for SARS-CoV-2 entry into host cells. Upon internalization into early endosomes (EEs), the virus is transported to late endosomes (LEs), where acidic conditions facilitate spike protein processing and viral genome release. Dynein and kinesin motors drive EE transport along microtubules; dynein moves EEs to the perinuclear region, while kinesins direct them towards the plasma membrane, creating a tug-of-war over the direction of transport.

Acidification of the phagosome orchestrates the motor forces directing its transport.

Phagosomes are dynamic organelles formed by macrophages to capture and destroy microbial pathogens. Phagosome transport from the cell periphery to the perinuclear region, is essential for fusion with lysosomes and the elimination of pathogens. Molecular motors, kinesin and dynein, generate opposing forces, transporting the phagosome away from and towards the lysosome, respectively.

Ultrafast Force-Clamp Spectroscopy of Microtubule-Binding Proteins.

Optical trapping has been instrumental for deciphering translocation mechanisms of the force-generating cytoskeletal proteins. However, studies of the dynamic interactions between microtubules (MTs) and MT-associated proteins (MAPs) with no motor activity are lagging. Investigating the motility of MAPs that can diffuse along MT walls is a particular challenge for optical-trapping assays because thermally driven motions rely on weak and highly transient interactions.

The sodium proton exchanger NHE9 regulates phagosome maturation and bactericidal activity in macrophages.

Acidification of phagosomes is essential for the bactericidal activity of macrophages. Targeting machinery that regulates pH within the phagosomes is a prominent strategy employed by various pathogens that have emerged as major threats to public health. Nascent phagosomes acquire the machinery for pH regulation through a graded maturation process involving fusion with endolysosomes.

Mitosis. Microtubule detyrosination guides chromosomes during mitosis.

Before chromosomes segregate into daughter cells, they align at the mitotic spindle equator, a process known as chromosome congression. Centromere-associated protein E (CENP-E)/Kinesin-7 is a microtubule plus-end-directed kinetochore motor required for congression of pole-proximal chromosomes. Because the plus-ends of many astral microtubules in the spindle point to the cell cortex, it remains unknown how CENP-E guides pole-proximal chromosomes specifically toward the equator.

Autoregulatory mechanism for dynactin control of processive and diffusive dynein transport.

Dynactin is the longest known cytoplasmic dynein regulator, with roles in dynein recruitment to subcellular cargo and in stimulating processive dynein movement. The latter function was thought to involve the N-terminal microtubule-binding region of the major dynactin polypeptide p150(Glued), although recent results disputed this. To understand how dynactin regulates dynein we generated recombinant fragments of the N-terminal half of p150(Glued).

Calibration of optical tweezers for in vivo force measurements: how do different approaches compare?

There is significant interest in quantifying force production inside cells, but since conditions in vivo are less well controlled than those in vitro, in vivo measurements are challenging. In particular, the in vivo environment may vary locally as far as its optical properties, and the organelles manipulated by the optical trap frequently vary in size and shape. Several methods have been proposed to overcome these difficulties.

Casein kinase 2 reverses tail-independent inactivation of kinesin-1.

Kinesin-1 is a plus-end microtubule-based motor, and defects in kinesin-based transport are linked to diseases including neurodegeneration. Kinesin can auto-inhibit via a head-tail interaction, but is believed to be active otherwise. Here we report a tail-independent inactivation of kinesin, reversible by the disease-relevant signalling protein, casein kinase 2 (CK2).

Mechanical stochastic tug-of-war models cannot explain bidirectional lipid-droplet transport.

Intracellular transport via the microtubule motors kinesin and dynein plays an important role in maintaining cell structure and function. Often, multiple kinesin or dynein motors move the same cargo. Their collective function depends critically on the single motors' detachment kinetics under load, which we experimentally measure here.