Fig. 3. Changes in polymyxin composition affect the propensity to form crystalline structures.
a Schematic representation of the polymyxin structure, where polymyxin E has D-Leu (L) and polymyxin B has D-Phe (F) in the 6th position. b, c AFM topographs of OM patches from the E. coli MG1655 WT strain upon incubation with different polymyxin E variants. Crystalline structures are formed with the enantiomer variant Thr10 (L- > D) and with full and intermediate-length polymyxin E variants. Structures are not formed in the polymyxin variant Dab9 (+) -> (-) and polymyxin E nonapeptide variant. d AFM topographs of OM patches from the E. coli MG1655 WT strain upon incubation with polymyxin B and polymyxin B nonapeptide variants. Crystalline structures are formed in both cases. OM patches were incubated with 50 mg/l of the polymyxin variant. For b–d, each experiment was repeated independently at least three times with the same results. Scale bars, 20 nm.