On physical properties of tetraether lipid membranes: effects of cyclopentane rings

Abstract

This paper reviews the recent findings related to the physical properties of tetraether lipid membranes, with special attention to the effects of the number, position, and configuration of cyclopentane rings on membrane properties. We discuss the findings obtained from liposomes and monolayers, composed of naturally occurring archaeal tetraether lipids and synthetic tetraethers as well as the results from computer simulations. It appears that the number, position, and stereochemistry of cyclopentane rings in the dibiphytanyl chains of tetraether lipids have significant influence on packing tightness, lipid conformation, membrane thickness and organization, and headgroup hydration/orientation.

Figure 1

Illustrations of the molecular structures of the bipolar tetraether lipids in the polar lipid fraction E (PLFE) isolated from S. acidocaldarius. PLFE contains (a) GDGT (or caldarchaeol) and (b) GDNT (or calditolglycerocaldarchaeol). The number of cyclopentane rings in each biphytanyl chain can vary from 0 to 4. The different head groups of GDNT and GDGT are presented at the bottom. GDG(N)T-0 and GDG(N)T-4 contain 0 and 4 cyclopentane rings per molecule, respectively (taken from [5], reproduced with permission).

Figure 2

Adiabatic compressibilities (k _S ^o) of PLFE liposomes derived from cells grown at three different temperatures: 68°C (dark squares), 76°C (open circles), and 81°C (open triangles). Solid line: DPPC liposomes for comparison (taken from [6], reproduced with permission).

Figure 3

Structures of cyclopentane ring containing GDGTs previously reported to exist in archaea [7]. The number of cyclopentane rings in the first and second hydrocarbon chains is indicated in the parentheses. The mass-to-charge ratio (m/z) of the protonated form [M+H]⁺ for each structure is also listed.

Figure 4

Synthetic tetraether lipids that have been used to study the effect of configuration (Compounds 1 and 2 [8, 9]) and position (Compounds 3 and 4 [10]) of the cyclopentane rings on membrane properties.