Dynamics of FtsI, an Essential Bacterial Cell Wall Synthesis Protein

Abstract

Bacterial cell division is complicated, requiring the orchestration of over thirty different proteins at midcell. One essential member of the septal cell wall peptidoglycan synthesis machinery, FtsI (PBP3), cross-links newly-made glycan strands and helps drive membrane invagination, exhibiting directional movement coupled to the treadmilling tubulin homologue FtsZ. However, how FtsZ regulates the spatiotemporal dynamics of FtsI indirectly through a protein-protein interaction relay in not well understood. Namely, whether or not FtsI's enzymatic activity contributes to its directional movement at the septum and how FtsI communicates with the Z-ring and other cell wall remodelers to advance division remain unknown. We have constructed functional fluorescent fusions of FtsI in the E. coli chromosome and have determined that the directional FtsI molecules are likely the active subpopulation. Through single molecule tracking and super-resolution microscopy, we tracked FtsI in Escherichia coli to determine its dynamics with point mutants that perturb its interaction with divisome partners or that reduce its enzymatic activity. We are currently testing FtsI interaction mutants between its critical partners to parse out the communication relay of the divisome.