Physical Properties of Archaeal Tetraether Lipid Membranes As Revealed by Differential Scanning and Pressure Perturbation Calorimetry, Molecular Acoustics, and Neutron Reflectometry: Effects of Pressure and Cell Growth Temperature

Abstract

The polar lipid fraction E (PLFE) is a major tetraether lipid component in the thermoacidophilic archaeon Sulfolobus acidocaldarius. Using differential scanning and pressure perturbation calorimetry as well as ultrasound velocity and density measurements, we have determined the compressibilities and volume fluctuations of PLFE liposomes derived from different cell growth temperatures (T(g) = 68, 76, and 81 °C). The compressibility and volume fluctuation values of PLFE liposomes, which are substantially less than those detected from diester lipid membranes (e.g., DPPC), exhibit small but significant differences with T(g). Among the three T(g)s employed, 76 °C leads to the least compressible and most tightly packed PLFE membranes. This temperature is within the range for optimal cell growth (75-80 °C). It is known that a decrease in T(g) decreases the number of cyclopentane rings in archael tetraether lipids. Thus, our data enable us to present the new view that membrane packing in PLFE liposomes varies with the number of cyclopentane rings in a nonlinear manner, reaching maximal tightness when the tetraether lipids are derived from cells grown at optimal T(g)s. In addition, we have studied the effects of pressure on total layer thickness, d, and neutron scattering length density, ρ(n), of a silicon-D(2)O interface that is covered with a PLFE membrane using neutron reflectometry (NR). At 55 °C, d and ρ(n) are found to be rather insensitive to pressure up to 1800 bar, suggesting minor changes of the thickness of the membrane's hydrophobic core and headgroup orientation upon compression only.

Probing volumetric properties of biomolecular systems by pressure perturbation calorimetry (PPC) – The effects of hydration, cosolvents and crowding

“…The partial specific isothermal compressibility of the solute, j o T , is given by Generally, c p and a are directly related to fluctuation parameters [11,41]. The square average of the enthalpy fluctuations, hDH 2 i, is related to the heat capacity, c p , of the system by hDH 2 i ¼ RT 2 c p , and the covariance between H and V fluctuations is related to the expansivity, hDH DVi ¼ RT 2 Va, i.e., the coefficient of thermal expansion is a parameter that is characterized by thermal and the mechanical fluctuation parameters, i.e., is proportional to the cross correlation of the volume and enthalpy fluctuations.…”

“…The square average of the enthalpy fluctuations, hDH 2 i, is related to the heat capacity, c p , of the system by hDH 2 i ¼ RT 2 c p , and the covariance between H and V fluctuations is related to the expansivity, hDH DVi ¼ RT 2 Va, i.e., the coefficient of thermal expansion is a parameter that is characterized by thermal and the mechanical fluctuation parameters, i.e., is proportional to the cross correlation of the volume and enthalpy fluctuations. The square average of the volume fluctuations hDV 2 i of the solute is related to the isothermal compressibility data [11,32]:…”

“…This calorimeter has basically the same architecture as a power-compensation differential scanning calorimeter (DSC), but measures the heat flow into or out of a sample upon small isothermal pressure changes (of typically ±5 bar). The method can be applied to study the coefficient of thermal expansion, a, and relative volume changes, DV/V, of aqueous solutions and dispersions of chemical and biochemical systems, including amino acids, proteins, DNA and phospholipid vesicles, micellar systems, and polymers [1][2][3][4][5][6][7][8][9][10][11].…”

Lipids of Archaeal Viruses

“…The Acidianus bottle-shaped virus (ABV) virions were reported to contain a 9 nm thick envelope [63]. The lipid nature of this envelope, however, has not been reported and the estimated thickness of 9 nm is more than that of usual membranes of archaea [28, 58, 64, 65]. …”

Electron cryotomography of ESCRT assemblies and dividing Sulfolobus cells suggests that spiraling filaments are involved in membrane scission

“…Again like other ESCRT proteins, CdvA also contains a membrane-binding domain that is predicted to be largely α-helical in nature (Samson et al ., 2011). To withstand extreme conditions, the membranes of thermoacidophilic Archaea like S. acidocaldarius contain bipolar, tetraether-linked lipids (Zhai et al ., 2012). A major component of these lipids, called polar lipid fraction E, can form liposomes of varying sizes.…”