Biology subjects

Berger, C. L.

Publications and source records attributed to Berger, C. L..

3 recordsLinked to original sources

bioRxiv2018

Regulation of KIF1A motility via polyglutamylation of tubulin C-terminal tails

Axonal transport is a highly regulated cellular process responsible for site-specific neuronal cargo delivery. This process is mediated in part by KIF1A, a member of the kinesin-3 family of molecular motors. It is imperative that KIF1As highly efficient, superprocessive motility along microtubules is tightly regulated as misregulation of KIF1A cargo delivery is observed in many neurodegenerative diseases. However, the regulatory mechanisms responsible for KIF1As motility, and subsequent proper spatiotemporal cargo delivery, are largely unknown. One potential regulatory mechanism of KIF1A motility is through the posttranslational modifications (PTMs) of axonal microtubules. These PTMs, often occurring on the C-terminal tails of the microtubule tracks, act as molecular \"traffic signals\" helping to direct kinesin motor cargo delivery. Occurring on neuronal microtubules, C-terminal tail polygutamylation is known to be important for KIF1A cargo transport. KIF1As initial interaction with microtubule C-terminal tails is facilitated by the K-loop, a positively charged surface loop of the KIF1A motor domain. However, the K-loops role in KIF1A motility and response to perturbations in C-terminal tail polyglutamylation is underexplored. Using single-molecule imaging, we present evidence of KIF1As previously unreported pausing behavior on multiple microtubule structures. Further analysis revealed that these pauses link multiple processive segments together, contributing to KIF1As characteristic superprocessive run length. We further demonstrate that KIF1A pausing is mediated by a K-loop/polyglutamylated C-terminal tail interaction and is a regulatory mechanism of KIF1A motility. In summary, we introduce a new mechanism of KIF1A motility regulation, providing further insight into KIF1As role in axonal transport.

biophysics↗

bioRxiv2018

The Human Kinesin Kif18A’s Neck Linker Permits Navigation of Microtubule Bound Obstacles within the Mitotic Spindle

Mitotic chromosome alignment is essential for the robust separation of genetic material into daughter cells. In mammalian cells, this process requires the function of Kif18A, a kinesin-8 motor protein. Kif18A confines chromosome movement to the mitotic spindle equator by accumulating at the plus-ends of kinetochore microtubule bundles (K-fibers), where it functions to suppress K-fiber dynamics. It is not understood how the motor accumulates at K-fiber plus-ends, a difficult feat requiring the motor to navigate protein dense microtubule tracks. Our data indicate that Kif18As relatively long (17 amino acid) neck linker is required for the motors accumulation at K-fiber plus-ends. Shorter neck linker (sNL) variants of Kif18A display a deficiency in K-fiber accumulation, especially on K-fibers near the center of the spindle. This pattern correlates with the more uniform concentration of the microtubule bundling protein HURP on central K-fibers compared to peripheral K-fibers. Depletion of HURP permits Kif18A sNL to accumulate on central K-fibers, while HURP overexpression reduces wild-type Kif18As ability to accumulate on this same K-fiber subset. Furthermore, single molecule assays indicate that Kif18A sNL motors are less proficient at navigating microtubules coated with the microtubule associated protein tau. Taken together, these results support a model in which Kif18As neck linker length permits efficient navigation of obstacles such as HURP to reach K-fiber ends during mitosis.\n\nSignficiance StatementKinesin motor proteins play key roles in controlling chromosome alignment and segregation during cell division. The kinesin Kif18A confines chromosomes to the middle of the spindle by accumulating at the ends of microtubules attached to chromosomes. We show here that Kif18As ability to accumulate at the end of these microtubules requires navigation of microtubule-associated protein obstacles, and that this activity is imparted by a relatively long neck linker region. These findings demonstrate a molecular mechanism for navigation of densely populated microtubules inside a cell.

cell biology↗

bioRxiv2017

Tau directs intracellular trafficking by regulating the forces exerted by kinesin and dynein teams

Organelles, proteins, and mRNA are transported bidirectionally along microtubules by plus-end directed kinesin and minus-end directed dynein motors. Microtubules are decorated by microtubule-associated proteins (MAPs) that organize the cytoskeleton, regulate microtubule dynamics and modulate the interaction between motor proteins and microtubules to direct intracellular transport. Tau is a neuronal MAP that stabilizes axonal microtubules and crosslinks them into bundles. Dysregulation of tau leads to a range of neurodegenerative diseases known as tauopathies including Alzheimers disease (AD). Tau reduces the processivity of kinesin and dynein by acting as an obstacle on the microtubule. Single-molecule assays indicate that kinesin-1 is more strongly inhibited than kinesin-2 or dynein, suggesting tau might act to spatially modulate the activity of specific motors. To investigate the role of tau in regulating bidirectional transport, we isolated phagosomes driven by kinesin-1, kinesin-2, and dynein and reconstituted their motility along microtubules. We find that tau biases bidirectional motility towards the microtubule minus-end in a dose-dependent manner. Optical trapping measurements show that tau increases the magnitude and frequency of forces exerted by dynein through inhibiting opposing kinesin motors. Mathematical modeling indicates that tau controls the directional bias of intracellular cargoes through differentially tuning the processivity of kinesin-1, kinesin-2, and dynein. Taken together, these results demonstrate that tau modulates motility in a motor-specific manner to direct intracellular transport, and suggests that dysregulation of tau might contribute to neurodegeneration by disrupting the balance of plus- and minus-end directed transport.\n\nSynopsis and Graphical Table of ContentsWe isolated endogenous cargoes, along with a complement of kinesin-1, kinesin-2, and dynein motors, and reconstituted their bidirectional motility in vitro. We find that tau, a microtubule-associated protein that stabilizes microtubules in neuronal axons, directs bidirectional cargoes towards the microtubule minus end by tuning the balance of forces exerted by kinesin and dynein teams. These results suggest a general mechanism for regulating the transport of intracellular cargoes through modulating the relative activity of opposing motor teams.\n\n\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=82 SRC=\"FIGDIR/small/173609_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (31K):\norg.highwire.dtl.DTLVardef@8ba4e0org.highwire.dtl.DTLVardef@1f5945corg.highwire.dtl.DTLVardef@1df2f47org.highwire.dtl.DTLVardef@198f5d8_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗