The dimerization and topological specificity functions of MinE reside in astructurally autonomous C-terminal domain

Correct placement of the division septum in Escherichia coli requires the c o-ordinated action of three proteins, MinC, MinD and MinE. MinC and MinD in teract to form a non-specific division inhibitor that blocks septation at a ll potential division sites. MinE is able to antagonize MinCD in a topologi cally sensitive manner, as it restricts MinCD activity to the unwanted divi sion sites at the cell poles, Here, we show that the topological specificit y function of MinE residues in a structurally autonomous, trypsin-resistant domain comprising residues 31-88, Nuclear magnetic resonance (NMR) and cir cular dichroic spectroscopy indicate that this domain includes both alpha a nd beta secondary structure, while analytical ultracentrifugation reveals t hat 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 pep tide corresponding to MinE(1-22) indicates that this region forms a nascent helix in which the peptide rapidly interconverts between disordered (rando m coil) and alpha-helical conformations, This suggests that the N-terminal region of MinE may be poised to adopt an alpha-helical conformation when it interacts with the target of its anti-MinCD activity, presumably MinD.