Biology subjects

McClellan, M.

Publications and source records attributed to McClellan, M..

4 recordsLinked to original sources

bioRxiv2022

Rapid binding to protofilament edge sites facilitates tip tracking of EB1 at growing microtubule plus-ends

EB1 is a key cellular protein that delivers critical regulatory molecules throughout the cell via the tip-tracking of growing microtubule plus-ends. Thus, it is important to understand the mechanism for how EB1 efficiently tracks growing microtubule plus-ends. It is widely accepted that EB1 binds with higher affinity to GTP-tubulin subunits at the growing microtubule tip, relative to GDP-tubulin along the microtubule length. However, it is unclear whether this difference in affinity alone is sufficient to explain the tip-tracking of EB1 at growing microtubule tips. Previously, we found that EB1 binds to exposed microtubule protofilament-edge sites at a [~]70-fold faster rate than to closed-lattice sites, due to diffusional steric hindrance to binding. Thus, we asked whether rapid protofilament-edge binding could contribute to efficient EB1 tip tracking. A computational simulation with differential EB1 on-rates based on closed-lattice or protofilament-edge binding, and with EB1 off-rates that were dependent on tubulin hydrolysis state, recapitulated experimental EB1 tip tracking. To test this model, we used cell-free biophysical assays, as well as live-cell imaging, in combination with the chemotherapy drug Eribulin. We found that Eribulin blocked EB1 protofilament-edge binding, which led to a dramatic decrease in EB1 tip tracking on dynamic microtubules. We conclude that rapid EB1 binding to microtubule protofilament-edge sites increases the efficiency of EB1 tip tracking at the growing microtubule plus end.

cell biology↗

bioRxiv2020

Oxidative stress pathogenically remodels the cardiac myocyte cytoskeleton via structural alterations to the microtubule lattice

In the failing heart, the cardiac myocyte microtubule network is remodeled, which increases cellular stiffness and disrupts contractility, contributing to heart failure and death. However, the origins of this deleterious cytoskeletal reorganization are unknown. We now find that oxidative stress, a condition characteristic of failing heart cells, leads to cysteine oxidation of microtubules. Further, our electron and fluorescence microscopy experiments revealed regions of structural damage within the oxidized microtubule lattice. These damaged regions led to the lengthening, realignment, and acetylation of dynamic microtubules within cardiac myocytes. Thus, we found that oxidative stress acts inside of cardiac myocytes to facilitate a dramatic, pathogenic shift from a dynamic, multifaceted microtubule network into a highly acetylated, longitudinally aligned, and static microtubule network. Our results demonstrate how a disease condition characterized by oxidative stress can trigger a molecular oxidation event, which propagates a toxic cellular-scale transformation of the cardiac myocyte microtubule network.Competing Interest StatementThe authors have declared no competing interest.View Full Text

cell biology↗

bioRxiv2019

Structural state recognition facilitates tip tracking of EB1 at growing microtubule ends in cells

The microtubule binding protein EB1 specifically targets the growing ends of microtubules in cells, where EB1 facilitates the interactions of cellular proteins with microtubule plus-ends. Microtubule end targeting of EB1 has been attributed to high affinity binding of EB1 to GTP-tubulin that is present at growing microtubule ends. However, our 3D single-molecule diffusion simulations predicted a [~]6000% increase in EB1 arrivals to open, tapered microtubule tip structures relative to closed lattice conformations. Using quantitative fluorescence, single-molecule, and electron microscopy experiments, we found that the binding of EB1 onto opened, structurally disrupted microtubules was dramatically increased relative to closed, intact microtubules, regardless of hydrolysis state. Correspondingly, in cells, the conversion of growing microtubule ends from a tapered into a blunt configuration resulted in reduced EB1 targeting. Together, our results suggest that microtubule structural recognition, based on a fundamental diffusion-limited binding model, facilitates the tip tracking of EB1 at growing microtubule ends.

cell biology↗

bioRxiv2018

The non-canonical SMC protein SmcHD1 antagonises TAD formation on the inactive X chromosome

The inactive X chromosome (Xi) in female mammals adopts an atypical higher-order chromatin structure, manifested as a global loss of local topologically associated domains (TADs), and formation of two mega-domains. In this study we demonstrate that the non-canonical SMC family protein, SmcHD1, which is important for gene silencing on Xi, contributes to this unique chromosome architecture. Specifically, allelic mapping of the transcriptome and epigenome in SmcHD1 null cells revealed the appearance of sub-megabase domains defined by gene activation, CpG hypermethylation and depletion of Polycomb-mediated H3K27me3. These domains, which correlate with sites of SmcHD1 enrichment on Xi in wild-type cells, additionally adopt features of active X chromosome higher-order chromosome architecture, including partial restoration of TAD boundaries. Xi chromosome architecture changes also occurred in an acute SmcHD1 knockout model, but in this case, independent of Xi gene de-repression. We conclude that SmcHD1 is a key factor in antagonising TAD formation on Xi.

molecular biology↗