Cyclopropyl Lipids
Cyclopropyl fatty acids are derived from in situ methylenation of the double bond of the corresponding cis-unsaturated fatty acids, and they are often found in bacteria such as E.coli, Streptococcus, M.tuberculosis, and Salmonella. Cyclopropanation frequently occurs in response to exposure to adverse environmental conditions such increases in osmotic pressure, high temperatures, changes in pH, nutrient deprivation, and increases in alcohol content. Cyclopropanation is thought to play a role in pathogenesis in M.tuberculosis with cis-cyclopropanated mycolic acids correlating with a persistence of the pathogen; whereas, trans-cyclopropanated mycolic acids were found to play a role in restricting the virulence. To add further support to this idea, one study found that cis-cyclopropyl lipids, which are most common in bacteria, increase the fluidity of the plasma membrane while also inducing a more ordered state within the hydrocarbon chains providing rationale for increased stability against environmental factors and reduced permeability of toxic compounds. The same study found that trans-cyclopronatated lipids were less ordered which could provide an explanation for their role in mitigating virulence.
Reference:
Poger D, Mark AE. A ring to rule them all: the effect of cyclopropane Fatty acids on the fluidity of lipid bilayers. J Phys Chem B. 2015 Apr 30;119(17):5487-95. doi: 10.1021/acs.jpcb.5b00958. PMID: 25804677.
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