Effect of Ring Size in ω-Alicyclic Fatty Acids on the Structural and Dynamical Properties Associated with Fluidity in Lipid Bilayers

Abstract

Fatty acids containing a terminal cyclic group such as cyclohexyl and cycloheptyl are commonly found in prokaryotic membranes, especially in those of thermo-acidophilic bacteria. These so-called ω-alicyclic fatty acids have been proposed to stabilise the membranes of bacteria by reducing the fluidity in membranes and increasing lipid packing and lipid chain order. In this article, molecular dynamics simulations are used to examine the effect of 3-to 7-membered cycloalkyl saturated and unsaturated (cyclopent-2-enyl and phenyl) rings in ω-alicyclic fatty acyl chains on the structure (lipid packing, lipid chain order and fraction of gauche defects in the chains) and dynamics (lateral lipid diffusion) of a model lipid bilayer. It was found that ω-alicyclic chains in which the ring was saturated reduced lipid condensation and lowered chain order which would be associated with enhanced fluidity. However, this effect was limited. The lateral diffusion of the lipids diminished as the ring size increased. In particular, ω-cyclohexyl and ω-cycloheptyl acyl tails led to a decrease in lipid diffusion.In contrast, ω-alicyclic acyl chains that contain an unsaturated ring promoted membrane fluidity both in terms of changes in membrane structure and lipid diffusion. This may indicate that saturated and unsaturated terminal rings in ω-alicyclic fatty acids fulfil alternative functions within membranes. Overall, the simulations suggest that ω-alicyclic fatty acids in which the terminal ring is saturated might protect the membrane of thermo-acidophilic bacteria from high-temperature and low-pH conditions through a "dynamical barrier" that would limit lipid diffusion and transmembrane diffusion of undesired ions and molecules.

Inactivation efficacy and mechanisms of atmospheric cold plasma on Alicyclobacillus acidoterrestris: Insight into the influence of growth temperature on survival

“…There are five main types of fatty acids detected, namely myristic acid (C14:0), palmitic acid (C16:0), stearic acid (C18:0), cyclohexaneundecanoic acid (ω-cyclohexyl C17:0) and cyclopentanetridecanoic acid (ω-cyclopentane C18:0), which has good consistency with the results obtained by Zhao et al ( 3 ). In this study, A. acidoterrestris as an acidophilic heat-resistant bacterium and ω-cyclohexyl C17:0 and ω-cyclopentane C18:0 accounted for more than 80%, which is good in consistence with previous studies that ω-cyclic fatty acids appear in the cell membrane of acidophilic, heat-resistant bacteria, in which the proportion could reach 60 to 90% ( 35 , 36 ). The fatty acid components including C16:0, C18:0, ω-cyclohexyl C17:0, and ω-cyclopentane C18:0 showed a significant change under various culture temperatures.…”

“…The stacked loose ω-alicyclic fatty acids can protect acidophilus from high temperature and low pH conditions by forming a dynamic barrier that restricts lipid diffusion and H + transmembrane diffusion ( 36 ). However, different from the mechanism of high temperature and low acid action, various reactive oxygen species and reactive nitrogen components such as ozone, hydroxyl radicals, and singlet oxygen radicals generated by plasma treatment, which will damage the function of fatty acids, induce lipids, especially the peroxidation of unsaturated fatty acids even destroys the cell membrane and leads to cell lysis and bacterial death ( 25 , 41 ).…”

“…In a study, as compared with straight-chain fatty acids, cyclic fatty acids can reduce the trans-gauche isomerization of lipid chains, thereby increasing the order degree of lipid chains and the area of lipid layers, and reducing the fluidity of cell membranes ( 37 , 38 ). However, a study has shown that the loose packing of ω-alicyclic fatty acids in the cell membrane is in the disorder of lipid tails increasing membrane fluidity, and the larger the ring size (3- to 7-membered cycloalkyl) in ω-alicyclic fatty acids, the disorder degree is greater ( 36 ). On the other hand, the relative proportion of C16:0 and C18:0 also increased, i.e., from 4.36, 2.43% at 25°C and to 11.35 and 5.85%, at 55°C.…”

Naturally Derived Membrane Lipids Impact Nanoparticle-Based Messenger RNA Delivery

“…The unconventional and asymmetric tails in Cyclo PC may change the LNP stability by perturbing lipid packing. 39 While we varied structural lipids, DLin-MC3-DMA and DMG-PEG 2K were used as the cationic lipid and PEG lipid, respectively (Fig. 1a).…”