Unusual Lipids
About this figure: Naturally occurring ladderane phospholipids such as [5][3]PC (left) independently self-assemble into stable, fluid giant unilamellar vesicles (GUVs) under conditions similar to those required to make GUVs from conventional phospholipids. These vesicles (right) are found to have slower rates of lipid diffusion within the membrane plane as well as lower permeability to proton diffusion across the membrane bilayer.
While the canonical lipids found in mammalian cells have been extensively characterized, many unusual lipids are found in nature, some widespread, some unique to certain classes of organism. The Burns Group here at Stanford has pioneered methods for synthesizing very unusual lipids such as the ladderane lipids shown in the figure and found in anammox organisms that perform anaerobic metabolism converting nitrite and ammonia to nitrogen, and danicalipins, chlorosulfolipids found in certain algae whose organization in membranes is not understood. Working with the Burns group, we have used all of the tools used to characterize mammalian lipids to understand the self-assembly of these unusual lipids. Recent work on the ladderanes demonstrates that these highly unusual lipids form vesicles and supported bilayers much like more conventional lipids, but form membranes that are relatively impermeable to proton diffusion, likely a requirement of the anammoxosome—the organelle which composes the bulk of the anammox cell volume and is the site of the anammox reaction [323].
[323] “Ladderane phospholipids form a densely packed membrane with normal hydrazine and anomalously low proton/hydroxide permeability”, Frank R. Moss III, Steven R. Shuken, Jaron A. M. Mercer, Carolyn M. Cohen, Thomas M. Weiss, Steven G. Boxer, and Noah Z. Burns, Proceedings of the National Academy of Sciences, 115, 9098-9103 (2018).[pdf] [C&News Commentary]
[312] "Chemical Synthesis and Self-Assembly of a Ladderane Phospholipid", Jaron A. M. Mercer, Carolyn M. Cohen, Steven R. Shuken, Anna M. Wagner, Myles W. Smith, Frank R. Moss III, Matthew D. Smith, Riku Vahala, Alejandro Gonzalez-Martinez, Steven G. Boxer, Noah Z. Burns, Journal of the American Chemical Society, 138, 15845-15848 (2016). [pdf]