On the Origin of Microtubules’ High-Pressure Sensitivity

Abstract

For over 50 years, it has been known that the mitosis of eukaryotic cells is inhibited already at high hydrostatic pressure conditions of 30 MPa. This effect has been attributed to the disorganization of microtubules, the main component of the spindle apparatus. However, the structural details of the depolymerization and the origin of the pressure sensitivity have remained elusive. It has also been a puzzle how complex organisms could still successfully inhabit extreme high-pressure environments such as those encountered in the depth of oceans. We studied the pressure stability of microtubules at different structural levels and for distinct dynamic states using high-pressure Fourier-transform infrared spectroscopy and Synchrotron small-angle x-ray scattering. We show that microtubules are hardly stable under abyssal conditions, where pressures up to 100 MPa are reached. This high-pressure sensitivity can be mainly attributed to the internal voids and packing defects in the microtubules. In particular, we show that lateral and longitudinal contacts feature different pressure stabilities, and they define also the pressure stability of tubulin bundles. The intactness of both contact types is necessary for the functionality of microtubules in vivo. Despite being known to dynamically stabilize microtubules and prevent their depolymerization, we found that the anti-cancer drug taxol and the accessory protein MAP2c decrease the pressure stability of microtubule protofilaments. Moreover, we demonstrate that the cellular environment itself is a crowded place and accessory proteins can increase the pressure stability of microtubules and accelerate their otherwise highly pressure-sensitive de novo formation.

Compression-dependent microtubule reinforcement comprises a mechanostat which enables cells to navigate confined environments

“…The exact mechanism that causes the microtubule disassembly remains to be determined. Increasing hydrostatic pressure may directly induce microtubule depolymerization as has been shown previously ( 36 ). However, we cannot exclude that hydrostatic pressure indirectly affects microtubule stability, potentially downstream of mechanosensitive ion channels ( 37 ).…”

Effect of X-ray free-electron laser-induced shockwaves on haemoglobin microcrystals delivered in a liquid jet

“…These, as well as loosely folded loops or water-mediated structural interactions, are important for the structural flexibility intrinsic to protein functionality. Such "packing defects" and also the large solvent channels in protein crystals render proteins and their crystals sensitive to applied pressure 23,[25][26][27] . The identification of potential ligand binding pockets in protein structures is often an important step in rational drug design, with the size and shape of cavities determining putative binding site volumes 28 .…”

Molecular cancer cell responses to solid compressive stress and interstitial fluid pressure

“…Unlike normal bronchial epithelial cells, CL1-5 and A549 lung cancer cells responded to 20 mmHg pressure applied with a syringe pump, by assembling F-actin containing filopodia (Kao et al, 2017). A large number of studies that applied pressure through an external liquid reservoir or pump, have examined microtubule behavior at pressures of the order of MPa (Gao et al, 2018;Nishiyama, 2017;Nishiyama, Kimura, Nishiyama, & Terazima, 2009;Nishiyama, Shimoda, Hasumi, Kimura, & Terazima, 2010), but these pressures are orders of magnitude larger than those prevalent in cancers in vivo (Stylianopoulos et al, 2018).…”