page_title: Ladderane
section_title: Biological background
hierarchical_section_title: Ladderane / Biological background
caption_attribution_description: English: Ladderane lipids present in anammoxasomes.
context_page_description: In chemistry, a ladderane is an organic molecule containing two or more fused cyclobutane rings. The name arises from the resemblance of a series of fused cyclobutane rings to a ladder. Numerous synthetic approaches have been developed for the synthesis of ladderane compounds of various lengths. The mechanisms often involve [2 + 2] photocycloadditions, a useful reaction for creating strained 4-membered rings. Naturally occurring ladderanes have been identified as major components of the anammoxosome membrane of the anammox bacteria Planctomycetes.
context_section_description: Ladderanes were first identified in a rare group of anaerobic ammonium oxidizing (anammox) bacteria belonging to the phylum Planctomycetes. These bacteria sequester the catabolic anammox reactions to intracellular compartments called anammoxosomes. The anammox process involves the oxidation of ammonium to nitrogen gas with nitrite as the final electron acceptor. Intermediates in this process are two highly toxic compounds, hydrazine (N₂H₄) and hydroxylamine (NH₂OH). The oxidation process involves the generation of a proton gradient on the intracytoplasmic face of the anammoxosome. Dissipation of the proton gradient is coupled to the phosphorylation of ADP through membrane-bound ATPases.
  Anammoxosomes are enriched in the ladderane lipids shown at right. Analysis of the anammoxosome membranes from the bacterial species Borcadia anammoxidans and Kuenenia stuttgartiensis has revealed that ladderanes constitute greater than 50% of membrane lipids. The high abundance of ladderane lipids in the anammoxosome results in an exceptionally dense membrane with reduced permeability. The reduced permeability may decrease the passive diffusion of protons across the membrane that would dissipate the electrochemical gradient. This would be especially detrimental to anammox bacteria, due to the relatively slow anammox metabolism. The decreased permeability has also been hypothesized to sequester the highly toxic and mutagenic intermediates, hydrazine and hydroxylamine, which can readily diffuse through biomembranes. The loss of these key intermediates would damage key cellular components such as DNA, as well as reduce the catabolic efficiency of the cell.
caption: Ladderane lipids present in anammoxosomes
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