Transient Membrane-Linked FtsZ Assemblies Precede Z-Ring Formation in Escherichia Coli

Abstract

During the early stages of cytokinesis FtsZ protofilaments form a ring-like structure, the Z-ring, in most bacterial species and several clades of archaea. This cytoskeletal scaffold recruits downstream proteins essential for septal cell wall synthesis. Despite progress in understanding the dynamic nature of the Z-ring and its role in coordinating septal cell wall synthesis, the early stages of protofilament formation and subsequent assembly into the Z-ring are still not understood. Here we investigate a sequence of assembly steps that lead to the formation of the Z-ring in Escherichia coli using high temporal and spatial resolution imaging. Our data show that formation of the Z-ring is preceded by transient membrane-linked FtsZ assemblies. These assemblies form after attachment of short cytosolic protofilaments, which we estimate to be less than 20 monomers long, to the membrane. After attachment, the filaments become more stable and grow in size. Despite this stabilization the filament assemblies treadmill and show periods of rapid growth and shrinkage. The likely function of these dynamic FtsZ assemblies is to identify the proper location for the Z-ring in the cell via random sampling.

Keywords: cell division, FtsZ protofilament, the Z-ring, treadmilling, Escherichia coli, protein assembly, single molecule tracking, microfluidics