Reconstituting geometry-modulated protein patterns in membrane compartments.

Abstract

The MinCDE protein system from Escherichia coli has become one of the most striking paradigms of protein self-organization and biological pattern formation. The whole set of Min proteins is functionally active to position the divisome machinery by inhibiting Z ring assembly away from mid-cell. This is accomplished by an oscillation behavior between the cell poles, induced by the reaction between the two antagonistic proteins MinD and MinE, which has long caught the attention of quantitative biologists. Technical advances in fluorescence microscopy and molecular biology have allowed us in the past years to reconstitute this MinDE self-organization in cell-free environments on model membranes. We verified the compositional simplicity of protein systems principally required for biological pattern formation, and subjected the mechanism to quantitative biophysical analysis on a single-molecule level. On flat extended membranes, MinD and MinE self-organized into parallel propagating waves. Moreover, employing microsystems technology to construct membrane-clad soft polymer compartments mimicking the shape of native E. coli cells has further enabled us to faithfully reproduce Min protein oscillations. We further investigated the response of this self-organizing molecular system to three-dimensional compartment geometry. We could show that Min protein patterns depend strongly on the size and shape of the compartment, and the oscillation axis can only be preserved within a certain length interval and narrow width of the compartment. This renders the Min system a perfectly adapted oscillator to the bacterial cell geometry.