Fig. 4

Structure and function studies of MCR-4 colistin resistance. a Surface structure of MCR-4 with the PE lipid substrate-interactive cavity. b An enlarged illustration for a five residue-containing, Zn²⁺-binding motif. The five residues in Zn²⁺-binding motif of MCR-4 refer to E240, T278, H377, D452, and H453, respectively. c Surface illustration of MCR-4 rotated counter-clockwise (35°). d An enlarged view of the seven residue-containing domain involved in binding of MCR-4 the PE lipid substrate. The seven residues denote N104, T108, E112, S323, K326, H382, and H465, respectively. e Use of western blotting to assay the expression of MCR-4 and its 12 point-mutants in E. coli. The original blot is seen in Supplementary Figure 15b. f Site-directed mutagenesis analyses for the Zn²⁺-binding motif of MCR-4 in the context of colistin resistance using the colistin susceptibility tests. g Colistin susceptibility-based dissection of the PE-interactive residues of MCR-4 It is a representative result from three independent experiments