Work

Behaviors of individual microtubules and microtubule populations relative to critical concentrations: dynamic instability occurs when critical concentrations are driven apart by nucleotide hydrolysis

Year: 2019

Type: article

Abstract: ABSTRACT The concept of critical concentration (CC) is central to understanding behaviors of microtubules and other cytoskeletal polymers. Traditionally, these polymers are understood to have one CC, measured multiple ways and assumed to be the subunit concentration necessary for polymer assembly. However, this framework does not incorporate dynamic instability (DI), and there is work indicating that microtubules have two CCs. We use our previously established simulations to confirm that microtubules have (at least) two experimentally relevant CCs and to clarify the behaviors of individuals and populations relative to the CCs. At free subunit concentrations above the lower CC (CC IndGrow ), growth phases of individual filaments can occur transiently ; above the higher CC (CC PopGrow ), the population’s polymer mass will increase persistently . Our results demonstrate that most experimental CC measurements correspond to CC PopGrow , meaning “typical” DI occurs below the concentration traditionally considered necessary for polymer assembly. We report that [free tubulin] at steady state does not equal CC PopGrow , but instead approaches CC PopGrow asymptotically as [total tubulin] increases and depends on the number of stable microtubule seeds. We show that the degree of separation between CC IndGrow and CC PopGrow depends on the rate of nucleotide hydrolysis. This clarified framework helps explain and unify many experimental observations.

Source: Molecular Biology of the Cell

DOI: 10.1091/mbc.e19-02-0101