Collapse of Lipid Membranes into Distended Lipidic Cubic Phases at High Solvent Levels, Membrane Remodelling, and Self-Repair

Abstract

Performance plastics, such as poly(methyl methacrylate), underpin the modern economy. Global manufacturing of plastic precursors relies on fossil carbon sources, and the urgently needed shift toward renewable carbon use through biofermentation is hindered by the low tolerance of producer strains to methacrylate esters. The principal mode of butyl methacrylate cellular toxicity is membrane disruption. To understand this process, the conditions for membrane stability, and recovery after solvent shock, we investigate the phase stability of hydrated lipid membranes at high levels of a key intermediate, butyl methacrylate. We assess the role of cis- vs trans-unsaturation in 18-carbon chain phospholipids on butyl methacrylate-induced phase conversion and polymorphism. Using ssNMR, SAXS and cryoEM, we demonstrate the formation of stable lipidic cubic phases in hydrated lipid/solvent (cis-chain phospholipid lipid/butyl methacrylate) systems at a 1:6 molar ratio entirely lacking monoolein. Transient lipidic cubic phases form in trans-chain phospholipid/butyl methacrylate systems, which slowly convert to bilayers through a spontaneous "membrane healing" process during recovery after solvent shock. The observed bicontinuous nanostructures with a cubic phase architecture coexist with a stable, monocontinuous hydrated phase of the same morphology but with simpler topological connectivity, which demonstrates that phase stability in cubic phases does not require topological complementarity. We propose trans-lipid substitutions in membranes of fermentative strains as a key step toward sustainable production of methacrylate esters.

1

Generating surfaces and topology of LCPs. Primitive Im3m (A), gyroid Ia3d (B), and diamond Pn3m (C) phases over phase space [−2π, 2π] (top) and [−π, π] (bottom).

2

BMA molar fraction dictates the phase polymorphic conversions in hydrated DOPC ternary systems. Wideline ³¹P ssNMR spectra (A, B, E, F) and 1D SAXS diffraction patterns (C, D, G, H) from hydrated DOPC/BMA at molar ratios of 2:3 (A, C, red), 1:3 (B, D, yellow), 1:6 (C, E, green), and 1:9 (F, H, blue) at 20 °C. Reflection and phase assignment are detailed in Table S1 and Figure S2.

3

Lipid-phase coexistence in hydrated 1:6 DEPC/BMA ternary systems. Wideline ³¹P ssNMR shows a cubic phase (A) confirmed by SAXS diffraction from LCP with a lamellar contribution (B).

4

Phase evolution in DOPC (A) and DEPC (B) with a 1:6 lipid/BMA molar ratio at 20 °C. Wideline ³¹P ssNMR spectra recorded over 10 days reveal a stable LCP in DOPC/BMA, while DEPC/BMA phase coexistence underwent conversion to a bilayer phase by day 9.