Compressibilities and Volume Fluctuations of Archaeal Tetraether Liposomes

Abstract

Bipolar tetraether lipids (BTLs) are abundant in crenarchaeota, which thrive in both thermophilic and nonthermophilic environments, with wide-ranging growth temperatures (4-108°C). BTL liposomes can serve as membrane models to explore the role of BTLs in the thermal stability of the plasma membrane of crenarchaeota. In this study, we focus on the liposomes made of the polar lipid fraction E (PLFE). PLFE is one of the main BTLs isolated from the thermoacidophilic crenarchaeon Sulfolobus acidocaldarius. Using molecular acoustics (ultrasound velocimetry and densimetry), pressure perturbation calorimetry, and differential scanning calorimetry, we have determined partial specific adiabatic and isothermal compressibility, their respective compressibility coefficients, partial specific volume, and relative volume fluctuations of PLFE large unilamellar vesicles (LUVs) over a wide range of temperatures (20-85°C). The results are compared with those obtained from liposomes made of dipalmitoyl-L-α-phosphatidylcholine (DPPC), a conventional monopolar diester lipid. We found that, in the entire temperature range examined, compressibilities of PLFE LUVs are low, comparable to those found in gel state of DPPC. Relative volume fluctuations of PLFE LUVs at any given temperature examined are 1.6-2.2 times more damped than those found in DPPC LUVs. Both compressibilities and relative volume fluctuations in PLFE LUVs are much less temperature-sensitive than those in DPPC liposomes. The isothermal compressibility coefficient (β(T)(lipid)) of PLFE LUVs changes from 3.59 × 10(-10) Pa(-1) at 25°C to 4.08 × 10(-10) Pa(-1) at 78°C. Volume fluctuations of PLFE LUVs change only 0.25% from 30°C to 80°C. The highly damped volume fluctuations and their low temperature sensitivity, echo that PLFE liposomes are rigid and tightly packed. To our knowledge, the data provide a deeper understanding of lipid packing in PLFE liposomes than has been previously reported, as well as a molecular explanation for the low solute permeation and limited membrane lateral motion. The obtained results may help to establish new strategies for rational design of stable BTL-based liposomes for drug/vaccine delivery.

The Cell Membrane of Sulfolobus spp.—Homeoviscous Adaption and Biotechnological Applications

“…Albeit, the volume of the membrane is relatively constant between liposomes containing low and high amounts of cyclopentane rings [62]. In general, the compressibility, the relative change of volume in response to a change in environment conditions [63], of tetraether liposomes seems to be lower when compared to diester liposomes, meaning that TEL liposomes are less influenced by stressors such as temperature [64]. These experimental findings are backed by in silico results.…”

In situlabel-free static cytometry by monitoring spatiotemporal fluctuations of image gray values

“…20 This was further successfully applied on liquids 21,22 and suspensions of liposomes. 23,24 On the other hand, since permittivity ε and refractive index n are mass-density and temperature-dependent, fluctuation in the latter two is expected to produce fluctuation in the permittivity and refractive index of a liquid medium as is generally expected, and in intracellular content as well, following the equation: 21,22 E Q -T A R G E T ; t e m p : i n t r a l i n k -; s e c 3 . 4 ; 3 2 6 ; 1 9 0…”

Mechanical properties of Ester- and Ether-DPhPC bilayers: a molecular dynamics study

“…In contrast to lipids of other cells, most Archaeal lipids have regularly branched tails that are linked to the head groups via ether linkage. As a result of their unique lipid structure, Archaeal membranes are more stable and have a lower permeability to ions and water [5], demonstrate a higher viscosity [6], and a higher density of packing [7].…”