The dimerization and topological specificity functions of MinE reside in a structurally autonomous C‐terminal domain

Correct placement of the division septum in Escherichia coli requires the co‐ordinated action of three proteins, MinC, MinD and MinE. MinC and MinD interact to form a non‐specific division inhibitor that blocks septation at all potential division sites. MinE is able to antagonize MinCD in a topologically sensitive manner, as it restricts MinCD activity to the unwanted division sites at the cell poles. Here, we show that the topological specificity function of MinE residues in a structurally autonomous, trypsin‐resistant domain comprising residues 31–88. Nuclear magnetic resonance (NMR) and circular dichroic spectroscopy indicate that this domain includes both α and β secondary structure, while analytical ultracentrifugation reveals that it also contains a region responsible for MinE homodimerization. While trypsin digestion indicates that the anti‐MinCD domain of MinE (residues 1–22) does not form a tightly folded structural domain, NMR analysis of a peptide corresponding to MinE1–22 indicates that this region forms a nascent helix in which the peptide rapidly interconverts between disordered (random coil) and α‐helical conformations. This suggests that the N‐terminal region of MinE may be poised to adopt an α‐helical conformation when it interacts with the target of its anti‐MinCD activity, presumably MinD.