Transportation of an Artifical Cargo by a Par-Min Hybrid System

Abstract

Spatial organization and active transportation of organelles are essential processes for cellular division. This is true even in bacteria, which were once thought too simple to require much internal organization. The ubiquitous deviant Walker ATPase family of proteins has been shown to be involved in systems important for spatial coordination in bacteria, the two most highly studied examples of which are the DNA partitioning Par system and the divisome positioning Min system. Both these systems contain the eponymous deviant Walker A ATPase (ParA or MinD), a protein which stimulates the ATPase's hydrolysis activity (ParB or MinE) and a cargo to be transported or localized (a “centromere” DNA site bound by ParB or the divisome inhibitor MinC bound to MinD). Despite the similarities of their components these systems appear to behave quite differently in vivo: the Par system segregates large clusters of ParB bound DNA cargo into sister cells during division by displacing ParA non-specifically bound to the nucleoid whereas the Min proteins bind the inner membrane and are seen to oscillate from one cell pole to the other. These differences may arise due to the nature of the binding surface (DNA vs lipid) or the nature of the cargo (a large cargo bound a large number of stimulator protein molecules in Par vs small protein molecules individually bound to membrane-bound MinD dimers). Here we use TIRF microscopy to demonstrate that the Min system is capable of transporting a magnetic bead (a large cargo) along a supported lipid bilayer in a manner strikingly similar to our previous reconstitution of the Par system. This demonstrates that despite their clear differences in their system dynamics under conditions for their natural functions, Par and Min systems operate based on common underlying mechanistic principles.