11 research outputs found
Modeling the Effects of Drug Binding on the Dynamic Instability of Microtubules
We propose a stochastic model that accounts for the growth, catastrophe and
rescue processes of steady state microtubules assembled from MAP-free tubulin.
Both experimentally and theoretically we study the perturbation of microtubule
dynamic instability by S-methyl-D-DM1, a synthetic derivative of the
microtubule-targeted agent maytansine and a potential anticancer agent. We find
that to be an effective suppressor of microtubule dynamics a drug must
primarily suppress the loss of GDP tubulin from the microtubule tip.Comment: 17 pages, 11 figures, to appear in Phys. Bio
TD-60 links RalA GTPase function to the CPC in mitosis
TD-60 (also known as RCC2) is a highly conserved protein that structurally resembles the Ran guanine exchange factor (GEF) RCC1, but has not previously been shown to have GEF activity. TD-60 has a typical chromosomal passenger complex (CPC) distribution in mitotic cells, but associates with integrin complexes and is involved in cell motility during interphase. Here we show that TD-60 exhibits GEF activity, in vitro and in cells, for the small GTPase RalA. TD-60 or RalA depletion causes spindle abnormalities in prometaphase associated with abnormal centromeric accumulation of CPC components. TD-60 and RalA apparently work together to contribute to the regulation of kinetochoreâmicrotubule interactions in early mitosis. Importantly, several mitotic phenotypes caused by TD-60 depletion are reverted by the expression of a GTP-locked mutant, RalA (Q72L). The demonstration that a small GTPase participates in the regulation of the CPC reveals a level of mitotic regulation not suspected in previous studies
A Molecular and Structural Mechanism for G Protein-mediated Microtubule Destabilization*
The heterotrimeric, G protein-coupled receptor-associated G protein, Gαs, binds tubulin with nanomolar affinity and disrupts microtubules in cells and in vitro. Here we determine that the activated form of Gαs binds tubulin with a KD of 100 nm, stimulates tubulin GTPase, and promotes microtubule dynamic instability. Moreover, the data reveal that the α3âÎČ5 region of Gαs is a functionally important motif in the Gαs-mediated microtubule destabilization. Indeed, peptides corresponding to that region of Gαs mimic Gαs protein in activating tubulin GTPase and increase microtubule dynamic instability. We have identified specific mutations in peptides or proteins that interfere with this process. The data allow for a model of the Gαs/tubulin interface in which Gαs binds to the microtubule plus-end and activates the intrinsic tubulin GTPase. This model illuminates both the role of tubulin as an âeffectorâ (e.g. adenylyl cyclase) for Gαs and the role of Gαs as a GTPase activator for tubulin. Given the ability of Gαs to translocate intracellularly in response to agonist activation, Gαs may play a role in hormone- or neurotransmitter-induced regulation of cellular morphology