Microtubule Plus End Dynamics − Do We Know How Microtubules Grow?

Microtubules grow by tubulin dimer addition to existing ends, a process central to eukaryotic microtubule function. This paper reviews current biochemical and ultrastructural concepts underlying microtubule polymerization, identifying points of consensus and ongoing debate. A model is proposed how cells optimize microtubule growth by independently controlling elongation and tube closure.

Microtubules form a highly dynamic filament network in all eukaryotic cells. Individual microtubules grow by tubulin dimer subunit addition and frequently switch between phases of growth and shortening. These unique dynamics are powered by GTP hydrolysis and drive microtubule network remodeling, which is central to eukaryotic cell biology and morphogenesis. Yet, our knowledge of the molecular events at growing microtubule ends remains incomplete. Here, recent ultrastructural, biochemical and cell biological data are integrated to develop a realistic model of growing microtubule ends comprised of structurally distinct but biochemically overlapping zones. Proteins that recognize microtubule lattice conformations associated with specific tubulin guanosine nucleotide states may independently control major structural transitions at growing microtubule ends. A model is proposed in which tubulin dimer addition and subsequent closure of the MT wall are optimized in cells to achieve rapid physiological microtubule growth.

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