Ladderane phospholipids form a densely packed membrane with normal hydrazine and anomalously low proton/hydroxide permeability

Abstract

Ladderane lipids are unique to anaerobic ammonium-oxidizing (anammox) bacteria and are enriched in the membrane of the anammoxosome, an organelle thought to compartmentalize the anammox process, which involves the toxic intermediate hydrazine (NH). Due to the slow growth rate of anammox bacteria and difficulty of isolating pure ladderane lipids, experimental evidence of the biological function of ladderanes is lacking. We have synthesized two natural and one unnatural ladderane phosphatidylcholine lipids and compared their thermotropic properties in self-assembled bilayers to distinguish between [3]- and [5]-ladderane function. We developed a hydrazine transmembrane diffusion assay using a water-soluble derivative of a hydrazine sensor and determined that ladderane membranes are as permeable to hydrazine as straight-chain lipid bilayers. However, pH equilibration across ladderane membranes occurs 5-10 times more slowly than across straight-chain lipid membranes. Langmuir monolayer analysis and the rates of fluorescence recovery after photobleaching suggest that dense ladderane packing may preclude formation of proton/hydroxide-conducting water wires. These data support the hypothesis that ladderanes prevent the breakdown of the proton motive force rather than blocking hydrazine transmembrane diffusion in anammox bacteria.

Membrane constriction and thinning by sequential ESCRT-III polymerization

“…The buffer-subtracted and averaged data were fit using a model for unilamellar vesicles ( 76 ) as previously described ( 77 ). The electron density profile of the bilayer is approximated by three Gaussian peaks corresponding to the inner and outer phosphate peaks and a negative peak at the center for the hydrocarbon region.…”

Lessons in Strain and Stability: Enantioselective Synthesis of (+)‐[5]‐Ladderanoic Acid

“…Ther equisite ester 9 was prepared by oxidation of the known [3]-ladderane ester 11 (Scheme 3B). [4a] Irradiation of 9 and 1,2-dichloroethylene with UVA( l max = 350 nm) or UVB (l max = 313 nm) failed to promote conversion of the starting materials.H owever,u se of UVC (l max = 254 nm) allowed consumption of 9.Unfortunately,the expected cycloadduct 10 was not detected, but rather ar emarkable conversion into ethylene (13)and methyl benzoate (12)was observed.…”

Performance of Anammox Processes for Wastewater Treatment: A Critical Review on Effects of Operational Conditions and Environmental Stresses

“…Furthermore, at high latitudes, anammox bacteria decrease their growth rate owing to the decrease in enzyme activity, density of cytoplasm, and low mass transfer rate [12,49,51]. Moreover, operating anammox systems at low temperatures can stimulate an increase in the amount of ladderane fatty acids, which reduce membrane permeability and passive diffusion of protons out of the anammoxosome, and this prevents ATP synthesis, thereby reducing metabolism [41,[52][53][54]. The instability of temperature in the mainstream and sidestream anammox processes makes extrapolation in operational design and maintenance challenging [55,56].…”