Understanding phospholipid function: Why are there so many lipids?

Abstract

In the 1970s, phospholipids were still considered mere building blocks of the membrane lipid bilayer, but the subsequent realization that phospholipids could also serve as second messengers brought new interest to the field. My own passion for the unique amphipathic properties of lipids led me to seek other, non-signaling functions for phospholipids, particularly in their interactions with membrane proteins. This seemed to be the last frontier in protein chemistry and enzymology to be conquered. I was fortunate to find my way to Eugene Kennedy's laboratory, where both membrane proteins and phospholipids were the foci of study, thus providing a jumping-off point for advancing our fundamental understanding of lipid synthesis, membrane protein biosynthesis, phospholipid and membrane protein trafficking, and the cellular roles of phospholipids. After purifying and characterizing enzymes of phospholipid biosynthesis in Escherichia coli and cloning of several of the genes encoding these enzymes in E. coli and Saccharomyces cerevisiae, I was in a position to alter phospholipid composition in a systematic manner during the cell cycle in these microorganisms. My group was able to establish, contrary to common assumption (derived from the fact that membrane proteins retain activity in detergent extracts) that phospholipid environment is a strong determining factor in the function of membrane proteins. We showed that molecular genetic alterations in membrane lipid composition result in many phenotypes, and uncovered direct lipid-protein interactions that govern dynamic structural and functional properties of membrane proteins. Here I present my personal "reflections" on how our understanding of phospholipid functions has evolved.

Immunological Aspects of Trichomonas vaginalis Infection in Women Attending Maternity Teaching Hospital and Some Public Health Centers in Erbil Governorate, Northern Iraq

“…Such elevated levels of these autoantibodies could be explained by the antigenic mimicry between the parasite antigens and host proteins, as cardiolipin and phospholipids are abundant in most cells of multicellular organisms, the former is an important component of the inner mitochondrial membrane, where it constitutes about 20% of the total lipid composition, [27,28] while phospholipids are a class of lipids and are a major component of all cell membranes as they can form lipid bilayers. [29] In respect to our results, the detection of significant titers of anticardiolipin IgG, IgM, and antiphospholipid IgG in the sera of trichomoniasis cases may be explained by the fact that all the infected women were chronic cases as they have been infected weeks before seeking medical advice. That is why IgG antibodies against both cardiolipin and phospholipids were detected in their sera.…”

Network Analysis Provides Insight into Tomato Lipid Metabolism

“…Unlike seeds, tomato fruit and leaf cells do not accumulate high amounts of storage lipids. Lipophilic compounds in tomato fruits and leaves participating mainly in signaling, membrane structure, and development [66][67][68][69].…”

Life without air

“…Our results with lipid structures very different from those found in A. laidlawii added credence to the theory that biological membranes contain mixtures of bilayer-forming and nonbilayer-forming lipids to achieve a balance of forces. This concept has been strengthened by work with other organisms, including E. coli, as discussed by William Dowhan in his Reflections article (39). As proposed by Lindblom and colleagues (40,41), cells appear to live within a narrow window where their membranes are in a physical state between the gel phase and the formation of nonbilayer aggregates.…”