Tubulin and Microtubules


The protein tubulin is the principal constituent of microtubules, whose dynamic behaviour allows them to perform a vital role in various forms of cell motility. Found in almost all types of eukaryotic cell, microtubules are an essential component of cell division, provide tracks for the transport of cellular organelles and vesicles and are responsible for the relative positioning of cellular compartments.

Keywords: dynamic instability; motility; microtubule lattices; GTP hydrolysis

Figure 1.

Structure of microtubules. (a) Atomic structure of the αβ‐tubulin heterodimer shown as a ribbon diagram; α helices in blue, β sheet in green. Taxol and GDP (bound to β‐tubulin) and GTP (bound to α‐tubulin in a position equivalent to that of GDP in β‐tubulin) are shown as space‐filling atoms. Each subunit has two globular domains separated by the core helix. (b) Assembly of heterodimers into longitudinal protofilaments, which in turn associate into sheets and microtubules. Side‐to‐side association of the protofilaments can produce an A‐lattice (symmetrical for the 13‐protofilament microtubule shown) or a B‐lattice with an A‐lattice‐like seam, or a more mixed lattice. (c) Stabilization of the polymer by microtubule‐associated proteins (MAPs). A widespread family, including tau, contains sequence repeats (coloured purple in the model shown here) that bind to the inside surface of a microtubule in a similar site to taxol (which is present in the solved atomic structure). Flanking regions (blue and grey) also help tau bind to tubulin. Tubulin's negatively‐charged C‐termini (small red projections) interact with positive charges on tau and other MAPs. The large red projections represent the negatively‐charged projection domain of tau.

Figure 2.

Vertebrate mitotic spindle in metaphase (chromosomes paired at the centre) and anaphase (chromosomes moving towards the poles). Each pole acts as the focus for a microtubule aster and contains a pair of centrioles surrounded by a cloud of protein. Microtubule minus ends are closer to the poles.

Figure 3.

(a) Cross‐section through a typical axoneme, viewed from the tip, i.e. from the plus ends of the microtubules. (b) Enlarged cross‐section of one of the doublet microtubules. Nine doublet microtubules and a central core structure are linked together by a complex variety of accessory molecules.



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Further Reading

Amos LA (2000) Focusing in on microtubules. Current Opinion in Structural Biology 10: 236–241.

Cassimeris L (1999) Accessory protein regulation of microtubule dynamics throughout the cell cycle. Current Opinion in Cell Biology 11: 134–141.

Erickson HP and Stoffler D (1996) Protofilaments and rings, two conformations of the tubulin family conserved from bacterial FtsZ to alpha/beta and gamma tubulin. Journal of Cell Biology; 135: 5–8.

Greene E, Henikoff S and Endo S (1999) The Kinesin Home Page. [http://proweb.org/kinesin//index.html] and its European mirror site [http://mc11.mcri.ac.uk/khome/].

Rieders CL and Salmon ED (1998) The vertebrate cell kinetochore and its roles during mitosis. Trends in Cell Biology 8: 310–318.

Schuyler SC and Pellman D (2001) Microtubule ‘plus‐end‐tracking proteins’: the end is just the beginning. Cell 105: 421–424.

Wittmann T, Hyman A and Desai A (2001) The spindle: a dynamic assembly of microtubule motors. Nature Cell Biology 3: E28–E34.

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Amos, Linda A(May 2005) Tubulin and Microtubules. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0003890]