Characterization of C-terminal structure of MinC and its implication in evolution of bacterial cell division

Proper cell division at the mid-site of Gram-negative bacteria reflects stringent regulation by the min system (MinC, MinD and MinE). Herein we report crystal structure of the C-terminal domain of MinC from Escherichia coli ( Ec MinC CTD ). The MinC CTD beta helical domain is engaged in a tight homodimer, similar to Thermotoga maritima MinC CTD ( Tm MinC CTD ). However, both Ec MinC CTD and Tm MinC CTD lack an α-helix (helix3) at their C-terminal tail, in comparison to Aquifex aerolicu MinC CTD ( Aa MinC CTD ) which forms an extra interaction interface with MinD. To understand the role of this extra binding element in MinC/MinD interactions, we fused this helix ( Aa helix3) to the C-terminus of Ec MinC and examined its effect on cell morphology and cell growth. Our results revealed that Aa helix3 impaired normal cell division in vivo . Furthermore, results of a co-pelleting assay and binding free energy calculation suggested that Aa helix3 plays an essential role in Aa MinCD complex formation, under the circumstance of lacking MinE in A. aerolicu . Combining these results with sequence analysis of MinC and MinD in different organisms, we propose an evolutionary relationship to rationalize different mechanisms in cell division positioning in various organisms.