77,195 research outputs found
Ectopic A-lattice seams destabilize microtubules
Natural microtubules typically include one A-lattice seam within an otherwise helically symmetric B-lattice tube. It is currently unclear how A-lattice seams influence microtubule dynamic instability. Here we find that including extra A-lattice seams in GMPCPP microtubules, structural analogues of the GTP caps of dynamic microtubules, destabilizes them, enhancing their median shrinkage rate by >20-fold. Dynamic microtubules nucleated by seeds containing extra A-lattice seams have growth rates similar to microtubules nucleated by B-lattice seeds, yet have increased catastrophe frequencies at both ends. Furthermore, binding B-lattice GDP microtubules to a rigor kinesin surface stabilizes them against shrinkage, whereas microtubules with extra A-lattice seams are stabilized only slightly. Our data suggest that introducing extra A-lattice seams into dynamic microtubules destabilizes them by destabilizing their GTP caps. On this basis, we propose that the single A-lattice seam of natural B-lattice MTs may act as a trigger point, and potentially a regulation point, for catastrophe
Microtubules in Bacteria: Ancient Tubulins Build a Five-Protofilament Homolog of the Eukaryotic Cytoskeleton
Microtubules play crucial roles in cytokinesis, transport, and motility, and are therefore superb targets for anti-cancer drugs. All tubulins evolved from a common ancestor they share with the distantly related bacterial cell division protein FtsZ, but while eukaryotic tubulins evolved into highly conserved microtubule-forming heterodimers, bacterial FtsZ presumably continued to function as single homopolymeric protofilaments as it does today. Microtubules have not previously been found in bacteria, and we lack insight into their evolution from the tubulin/FtsZ ancestor. Using electron cryomicroscopy, here we show that the tubulin homologs BtubA and BtubB form microtubules in bacteria and suggest these be referred to as “bacterial microtubules” (bMTs). bMTs share important features with their eukaryotic counterparts, such as straight protofilaments and similar protofilament interactions. bMTs are composed of only five protofilaments, however, instead of the 13 typical in eukaryotes. These and other results suggest that rather than being derived from modern eukaryotic tubulin, BtubA and BtubB arose from early tubulin intermediates that formed small microtubules. Since we show that bacterial microtubules can be produced in abundance in vitro without chaperones, they should be useful tools for tubulin research and drug screening
A continuous model for microtubule dynamics with catastrophe, rescue and nucleation processes
Microtubules are a major component of the cytoskeleton distinguished by
highly dynamic behavior both in vitro and in vivo. We propose a general
mathematical model that accounts for the growth, catastrophe, rescue and
nucleation processes in the polymerization of microtubules from tubulin dimers.
Our model is an extension of various mathematical models developed earlier
formulated in order to capture and unify the various aspects of tubulin
polymerization including the dynamic instability, growth of microtubules to
saturation, time-localized periods of nucleation and depolymerization as well
as synchronized oscillations exhibited by microtubules under various
experimental conditions. Our model, while attempting to use a minimal number of
adjustable parameters, covers a broad range of behaviors and has predictive
features discussed in the paper. We have analyzed the resultant behaviors of
the microtubules changing each of the parameter values at a time and observing
the emergence of various dynamical regimes.Comment: 25 pages, 12 figure
Segregation of a microsporidian parasite during host cell mitosis
We investigated the segregation of an intracellular microsporidian parasite during host cell division. A time-course
experiment was carried out to examine the distribution of parasites relative to host chromosomal DNA via light and
electron microscopy. Fluorescent light microscopy and EM studies showed that the parasite lay in the perinuclear zone
of the host cell during interphase and segregated to daughter cells at mitosis. At metaphase, the parasite was frequently
closely associated with host microtubules and mitochondria. Electron-dense bridges were observed between the parasites
and the host microtubules and also between host mitochondria and microtubules. The study suggests that both the parasite
and the host cell organelles segregate in association with spindle microtubules
Microtubule dynamics depart from wormlike chain model
Thermal shape fluctuations of grafted microtubules were studied using high
resolution particle tracking of attached fluorescent beads. First mode
relaxation times were extracted from the mean square displacement in the
transverse coordinate. For microtubules shorter than 10 um, the relaxation
times were found to follow an L^2 dependence instead of L^4 as expected from
the standard wormlike chain model. This length dependence is shown to result
from a complex length dependence of the bending stiffness which can be
understood as a result of the molecular architecture of microtubules. For
microtubules shorter than 5 um, high drag coefficients indicate contributions
from internal friction to the fluctuation dynamics.Comment: 4 pages, 4 figures. Updated content, added reference, corrected typo
Sulfo-SMCC Prevents Annealing of Taxol-Stabilized Microtubules In Vitro
Microtubule structure and functions have been widely studied in vitro and in
cells. Research has shown that cysteines on tubulin play a crucial role in the
polymerization of microtubules. Here, we show that blocking sulfhydryl groups
of cysteines in taxol-stabilized polymerized microtubules with a commonly used
chemical crosslinker prevents temporal end-to-end annealing of microtubules in
vitro. This can dramatically affect the length distribution of the
microtubules. The crosslinker sulfosuccinimidyl
4-(N-maleimidomethyl)cyclohexane-1-carboxylate, sulfo-SMCC, consists of a
maleimide and an N-hydroxysuccinimide ester group to bind to sulfhydryl groups
and primary amines, respectively. Interestingly, addition of a maleimide dye
alone does not show the same interference with annealing in stabilized
microtubules. This study shows that the sulfhydryl groups of cysteines of
tubulin that are vital for the polymerization are also important for the
subsequent annealing of microtubules.Comment: 3 figure
Effect of 2-H and 18-O water isotopes in kinesin-1 gliding assay
We show here the effects of heavy-hydrogen water (^2^H~2~O) and heavy-oxygen water (H~2~^18^O) on the gliding speed of microtubules on kinesin-1 coated surfaces. Increased fractions of isotopic waters used in the motility solution decreased the gliding speed of microtubules by a maximum of 21% for heavy-hydrogen and 5% for heavy-oxygen water. We discuss possible interpretations of these results and the importance for future studies of water effects on kinesin and microtubules. We also discuss the implication for biomolecular devices incorporating molecular motors
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