How Does Covalent Cross-Linking Enhance Thermal Robustness of Archaeal Tetraether Membranes? Insights from Molecular Dynamics Simulations

Hyperthermophilic archaea thrive at temperatures above 80 °C, with some species growing beyond 120 °C. At these extremes, how do they avoid membrane collapse? In this study, we examine the fundamental hypothesis that interchain cross-links in glycerol monoalkyl glycerol tetraethers (GMGTs) offer qualitatively better thermal protection than the non-cross-linked counterparts, glycerol dialkyl glycerol tetraethers (GDGTs), using all-atom molecular dynamics simulations. To capture the full thermal response of each membrane, including the onset of structural failure, which cannot be identified without deliberately exceeding the biological growth limit, we simulated pure GDGT-0 and GMGT-0 membranes across the temperature range of 95 to 155 °C. We demonstrate that GDGT-0 membranes undergo catastrophic structural failure above 125 °C, characterized by simultaneous headgroup compaction, chain splaying, and tilting followed by hydrogen-bond disruption. In striking contrast, the GMGT-0 membranes remain structurally intact throughout the entire temperature range investigated, showing only gradual, controlled compaction at the highest temperatures. These results show that a single covalent interchain cross-link fundamentally alters the membrane failure pathway, extending membrane stability by at least around 20 °C and preventing the collective structural rearrangements that trigger thermal collapse in GDGT membranes.