Archaeal Membrane Lipids and Applications

Abstract

Membrane lipids of Archaea are unique and distinct from those found in Eukarya and Bacteria . The polar lipids consist of isoprenoid chains, 20–40 carbons in length and usually saturated, which are attached via stable ether bonds to the glycerol carbons at the sn ‐2,3 positions. Polar head groups differ at the genus level of diversity and consist of mixtures of glyco groups (mainly disaccharides), and/or phospho groups primarily phosphoglycerol, phosphoserine, phosphoethanolamine or phosphoinositol. Phosphocholine headgroups are rarely found. Extremely halophilic archaea are characterised by headgroups consisting of phosphoglycerolphosphate‐ O ‐methyl, and sulfated‐sugars. Some of these archaea synthesise cardiolipin analogues. The inherent stability and unique features of archaeal lipids makes them a useful biomarker for Archaea within environmental samples, including ocean sediments. The polar lipids of Archaea can be used to make liposomes (closed vesicles referred to as archaeosomes) with characteristics that are useful for applications in biotechnology. Archaeal‐like polar lipids are being synthesised to optimise the properties of archaeosomes to serve as next‐generation adjuvants and drug delivery systems. Key Concepts: Archaeol (2,3‐diphytanyl‐ sn ‐glycerol), and variations thereof, define the polar lipids of the domain of life, Archaea . The structures of polar lipids biosynthesised provide a useful taxonomic feature to assign an isolate to the Genus level of classification. New polar lipid structures are being reported as the field expands to encompass novel isolates. These unique polar and neutral isoprenyl lipids can be used as biomarkers of archaea in environmental samples. Archaeal lipids can serve as a rich source for novel molecules not commonly found in nature, such as β‐ l ‐gulose. Archaeal polar lipid mixtures hydrate to form lipid membrane vesicles (archaeosomes) with bilayer, unilayer or a combination of uni and bilayer structure. Archaeosomes are generally nonfusogenic in vitro , but fusion can be dramatic for certain compositions by exposure to the combination of acidic pH, calcium and glycosidase. Archaeosomes function as safe vaccine adjuvants in mammals imparting long‐lasting CD8 + T‐cell immunity and antibody responses. Isoprenoid lipids that retain the key archaeal‐lipid features are being synthesised to optimise their properties as vaccine adjuvants and delivery systems.

Parameterization of the CHARMM All-Atom Force Field for Ether Lipids and Model Linear Ethers

“…C36e yields close agreement with experimental scattering factors for a DHPC bilayer in the NPT ensemble, making this comparison possible. The ether linkage is responsible for the experimentally lower water permeability of DHPC relative to DPPC and is thought to contribute to the resilience of archaeal membranes over a range of pH . C36e enables modeling of the effects of the ether linkage on membrane water permeability and stability over a range of salinities, pressures, and temperatures.…”

“…The comparable values for K A listed in Table 7 imply that the ether linkage does not contribute to the increased membrane stiffness observed in archaea. 43 In addition to the ether linkage, archaeal membranes contain methylated tails composed of repeating 5-carbon isopranoid or isoprenoid chains. Acyl chains with this structure have been shown to increase bilayer stiffness in simulations with C36 using esterlinked lipids.…”

Multiscale Simulations of Biological Membranes: The Challenge To Understand Biological Phenomena in a Living Substance

“…Archaea is a phyla not belonging to either bacteria or eukaryotes, but having many unusual molecular mechanisms (Figure ). − They have glycerol-based lipids with ether links. Typically, archaeal lipid chains are branched or polyprenyls.…”

Isoprenoid lipid chains increase membrane resistance to pore formation

“…Archaeal lipid tails are fully saturated (with rare exceptions) isoprenoid chains and sometimes contain cyclopropane and/or cyclohexane rings, which is also not typical for bacte ria and eukaryotes with their lipids generally being unbranched. Such structure of the hydrophobic part of the molecule not only helps the archaea to live at high temperatures, but also protects their membranes from harmful influence of various phospholipases, secreted by other organisms, and from oxidative stress [5]. However, the role of the branched chain structure in the permeability of archaeal membranes to various ions, gases and water is still an open question [2].…”