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#microtubule polymerization

2 public questions tagged with this topic.

Cytoskeleton

What is the function of XMAP215?

Microtubule growth in cells exceeds intrinsic tubulin addition rate due to polymerase action of Dis1 ch-TOG XMAP215 family enhancing incorporation efficiency. XMAP215 contains five Tumor Overexpressed Gene TOG domains each with two HEAT repeats capable of binding free alpha beta tubulin dimers with micromolar affinity. Mechanism involves processive tracking: TOG array recruits soluble dimers tethers to plus end via interaction with EB1 and lattice then delivers dimers to growing tip in orientation favoring incorporation increasing growth rate several fold. Function does not require ATP hydroly

Ref: Al-Bassam & Chang, Trends Cell Biol 2011 – XMAP215 polymerase binds tubulin dimers enhances polymerization rate.

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Cytoskeleton

In microtubule polymerization, which end exhibits faster growth?

Polarity of microtubules dictates directionality of transport and regulation by plus end tracking proteins +TIP network. Lattice assembled from head to tail alpha beta dimers creates structurally distinct ends with different chemistry. Minus end shows alpha tubulin outward typically embedded in gamma TuRC within MTOC exchange slow often capped by patronins CAMSAP family. Plus end exposes beta tubulin with GTP binding pocket capable of rapid subunit addition with on rate about 7 per micromolar per second versus minus about half. In vitro growth rates show plus about two to three fold faster elo

Ref: Alberts et al., Molecular Biology of the Cell, Chapter 14 – Plus end exhibits faster growth due to polarity.

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