15 research outputs found
Taxanes convert regions of perturbed microtubule growth into rescue sites
Microtubules are polymers of tubulin dimers, and conformational transitions in the microtubule
lattice drive microtubule dynamic instability and affect various aspects of microtubule function.
The exact nature of these transitions and their modulation by anti -cancer drugs such as Taxol and
epothilone, which can stabilize microtubules but also perturb their growth, are poorly understood.
Here, we directly visualize the action of fluorescent Taxol and epothilone derivatives and show
that microtubules can transition to a state that triggers cooperative drug binding to form regions
with altered lattice conformation. Such regions emerge at growing microtubule ends that are in a
pre-catastrophe state and inhibit microtubule growth and shortening. Electron microscopy and in
vitro dynamics data indicate that taxane accumulation zones represent incomplete tubes that can
persist, incorporate tubulin dimers and repeatedly induce microtubule rescues. Thus, taxanes
modulate the material properties of microtubules by converting destabilized growing microtubule
ends into regions resistant to depolymerization
Inhibiting parasite proliferation using a rationally designed anti-tubulin agent
Infectious diseases caused by apicomplexan parasites remain a global public health threat. The presence of multiple ligand-binding sites in tubulin makes this protein an attractive target for anti-parasite drug discovery. However, despite remarkable successes as anti-cancer agents, the rational development of protozoan parasite-specific tubulin drugs has been hindered by a lack of structural and biochemical information on protozoan tubulins. Here, we present atomic structures for a protozoan tubulin and microtubule and delineate the architectures of apicomplexan tubulin drug-binding sites. Based on this information, we rationally designed the parasite-specific tubulin inhibitor parabulin and show that it inhibits growth of parasites while displaying no effects on human cells. Our work presents for the first time the rational design of a species-specific tubulin drug providing a framework to exploit structural differences between human and protozoa tubulin variants enabling the development of much-needed, novel parasite inhibitors.
Natacha *#1, Ashwani *#1, Izra , Tianyang **3, Fiona **3, Alexander D. , Valentin , Mamata , Anthony J. , Carolyn A. , Naomi & Michel O.
Recommended from our members
A LOFAR observation of ionospheric scintillation from two simultaneous travelling ionospheric disturbances
This paper presents the results from one of the first observations of ionospheric scintillation taken using the Low-Frequency Array (LOFAR). The observation was of the strong natural radio source Cassiopeia A, taken overnight on 18â19 August 2013, and exhibited moderately strong scattering effects in dynamic spectra of intensity received across an observing bandwidth of 10â80 MHz. Delay-Doppler spectra (the 2-D FFT of the dynamic spectrum) from the first hour of observation showed two discrete parabolic arcs, one with a steep curvature and the other shallow, which can be used to provide estimates of the distance to, and velocity of, the scattering plasma. A cross-correlation analysis of data received by the dense array of stations in the LOFAR âcoreâ reveals two different velocities in the scintillation pattern: a primary velocity of ~20â40 msâ1 with a north-west to south-east direction, associated with the steep parabolic arc and a scattering altitude in the F-region or higher, and a secondary velocity of ~110 msâ1 with a north-east to south-west direction, associated with the shallow arc and a scattering altitude in the D-region. Geomagnetic activity was low in the mid-latitudes at the time, but a weak sub-storm at high latitudes reached its peak at the start of the observation. An analysis of Global Navigation Satellite Systems (GNSS) and ionosonde data from the time reveals a larger-scale travelling ionospheric disturbance (TID), possibly the result of the high-latitude activity, travelling in the north-west to south-east direction, and, simultaneously, a smaller-scale TID travelling in a north-east to south-west direction, which could be associated with atmospheric gravity wave activity. The LOFAR observation shows scattering from both TIDs, at different altitudes and propagating in different directions. To the best of our knowledge this is the first time that such a phenomenon has been reported
Comprehensive Analysis of Binding Sites in Tubulin
Tubulin plays essential roles in vital cellular activities and is the target of a wide range of proteins and ligands. Here, using a combined computational and crystallographic fragment screening approach, we addressed the question of how many binding sites exist in tubulin. We identified 27 distinct sites, of which 11 have not been described previously, and analyzed their relationship to known tubulin\u2013protein and tubulin\u2013ligand interactions. We further observed an intricate pocket communication network and identified 56 chemically diverse fragments that bound to 10 distinct tubulin sites. Our results offer a unique structural basis for the development of novel small molecules for use as tubulin modulators in basic research applications or as drugs. Furthermore, our method lays down a framework that may help to discover new pockets in other pharmaceutically important targets and characterize them in terms of chemical tractability and allosteric modulation
Actin-microtubule coordination at growing microtubule ends
To power dynamic processes in cells, the actin and microtubule cytoskeletons organize into complex structures. Although it is known that cytoskeletal coordination is vital for cell function, the mechanisms by which cross-linking proteins coordinate actin and microtubule activities remain poorly understood. In particular, it is unknown how the distinct mechanical properties of different actin architectures modulate the outcome of actinâmicrotubule interactions. To address this question, we engineered the protein TipAct, which links growing microtubule ends via end-binding proteins to actin filaments. We show that growing microtubules can be captured and guided by stiff actin bundles, leading to global actinâmicrotubule alignment. Conversely, growing microtubule ends can transport, stretch and bundle individual actin filaments, thereby globally defining actin filament organization. Our results provide a physical basis to understand actinâmicrotubule cross-talk, and reveal that a simple cross-linker can enable a mechanical feedback between actin and microtubule organization that is relevant to diverse biological contexts
Actin-microtubule coordination at growing microtubule ends
To power dynamic processes in cells, the actin and microtubule cytoskeletons organize into complex structures. Although it is known that cytoskeletal coordination is vital for cell function, the mechanisms by which cross-linking proteins coordinate actin and microtubule activities remain poorly understood. In particular, it is unknown how the distinct mechanical properties of different actin architectures modulate the outcome of actinâmicrotubule interactions. To address this question, we engineered the protein TipAct, which links growing microtubule ends via end-binding proteins to actin filaments. We show that growing microtubules can be captured and guided by stiff actin bundles, leading to global actinâmicrotubule alignment. Conversely, growing microtubule ends can transport, stretch and bundle individual actin filaments, thereby globally defining actin filament organization. Our results provide a physical basis to understand actinâmicrotubule cross-talk, and reveal that a simple cross-linker can enable a mechanical feedback between actin and microtubule organization that is relevant to diverse biological contexts
End-binding proteins sensitize microtubules to the action of microtubule-targeting agents
Microtubule-targeting agents (MTAs) are widely used for treatment of cancer and other diseases, and a detailed understanding of the mechanism of their action is important for the development of improved microtubule-directed therapies. Although there is a large body of data on the interactions of different MTAs with purified tubulin andmicrotubules,much less is known about how the effects of MTAs are modulated by microtubule-associated proteins. Among the regulatory factors with a potential to have a strong impact on MTA activity are the microtubule plus end-tracking proteins, which controlmultiple aspects of microtubule dynamic instability. Here,we reconstituted microtubule dynamics in vitro to investigate the influence of end-binding proteins (EBs), the core components of the microtubule plus end-tracking protein machinery, on the effects that MTAs exert onmicrotubule plus-end growth.We found that EBs promote microtubule catastrophe induction in the presence of all MTAs tested. Analysis of microtubule growth times supported the view that catastrophes aremicrotubule age dependent. This analysis indicated that MTAs affect microtubule aging in multiple ways: destabilizing MTAs, such as colchicine and vinblastine, accelerate aging in an EB-dependentmanner,whereas stabilizingMTAs, such as paclitaxel and peloruside A, induce not only catastrophes but also rescues and can reverse the aging process