Structural characterization of the essential cell division protein FtsE and its interaction with FtsX in Streptococcus pneumoniae

FtsEX is a membrane complex widely conserved across diverse bacterial genera and involved in critical processes such as recruitment of division proteins and in spatial and temporal regulation of muralytic activity during cell division or sporulation. FtsEX is a member of the ABC transporter superfamily, where FtsX is an integral membrane protein and FtsE is an ATPase, required for mechanotransmission of the signal from the cytosol through the membrane, to regulate the activity of cell-wall hydrolases in the periplasm. Both proteins are essential in the major human respiratory pathogenic bacterium, Streptococcus pneumoniae and interact with the modular peptidoglycan hydrolase PcsB at the septum. Here, we report the high-resolution structures of pneumococcal FtsE in complex with different nucleotides. Structural analysis reveals that FtsE contains all the conserved structural motifs associated with ATPase activity, and allowed interpretation of the in vivo dimeric arrangement in both ADP and ATP states. Interestingly, three specific FtsE regions were identified with high structural plasticity that shape the cavity in which the cytosolic region of FtsX would be inserted. The residues corresponding to the FtsX coupling helix, responsible for FtsE contact, were identified and validated by in vivo mutagenesis studies showing that this interaction is essential for cell growth and proper morphology. IMPORTANCEBacterial cell division is a central process that requires exquisite orchestration of both the cell wall biosynthetic and lytic machineries. The essential membrane complex FtsEX, widely conserved across bacteria, play a central role by recruiting proteins to the divisome apparatus and by regulating periplasmic muralytic activity from the cytosol. FtsEX is a member of the Type VII family of the ABC-superfamily but instead transporter, couple ATP hydrolysis by FtsE to mechanically transduce a conformational signal to activate PG hydrolases. So far, no structural information is available for FtsE. Here we provide the structural characterization of FtsE confirming its ATPase nature and revealing regions with high structural plasticity key for FtsX binding. The complementary region in FtsX has been also identified and validated in vivo. Our results provide evidences on how difference between ATP and ADP states in FtsE would dramatically alter FtsEX interaction with PG hydrolase PcsB in pneumococcal division.