An ATP-binding cassette transporter-like complex governs cell-wall hydrolysis at the bacterial cytokinetic ring

Abstract

ATP-binding cassette transporters are ubiquitous membrane protein complexes that move substrates across membranes. They do so using ATP-induced conformational changes in their nucleotide-binding domains to alter the conformation of the transport cavity formed by their transmembrane domains. In Escherichia coli , an ATP-binding cassette transporter-like complex composed of FtsE (nucleotide-binding domain) and FtsX (transmembrane domain) has long been known to be important for cytokinesis, but its role in the process has remained mysterious. Here we identify FtsEX as a regulator of cell-wall hydrolysis at the division site. Cell-wall material synthesized by the division machinery is shared initially by daughter cells and must be split by hydrolytic enzymes called “amidases” to drive daughter-cell separation. We recently showed that the amidases require activation at the cytokinetic ring by proteins with LytM domains, of which EnvC is the most critical. In this report, we demonstrate that FtsEX directly recruits EnvC to the septum via an interaction between EnvC and a periplasmic loop of FtsX. Importantly, we also show that FtsEX variants predicted to be ATPase defective still recruit EnvC to the septum but fail to promote cell separation. Our results thus suggest that amidase activation via EnvC in the periplasm is regulated by conformational changes in the FtsEX complex mediated by ATP hydrolysis in the cytoplasm. Since FtsE has been reported to interact with the tubulin-like FtsZ protein, our model provides a potential mechanism for coupling amidase activity with the contraction of the FtsZ cytoskeletal ring.

Structural basis of PcsB-mediated cell separation in Streptococcus pneumoniae

“…The conserved FtsEX complex recently emerged as a major regulator of PG hydrolysis during bacterial cell division 13,15,33 . FtsEX is essential or conditionally essential in a great variety of bacterial species 14,34 .…”

“…At the cytoplasmic side of the membrane, FtsX, which has four transmembrane segments, interacts with FtsE. An increasing body of knowledge indicates that the FtsEX complex is an essential regulator of murein-hydrolase activity in Gram-positive as well as Gram-negative bacteria 15 . FtsE is an ATPase, and it is therefore believed that ATP hydrolysis drives a conformational change in the FtsEX/PcsB complex that activates PcsB.…”

Mycobacterium tuberculosis FtsX extracellular domain activates the peptidoglycan hydrolase, RipC

“…The Z ring recruits and coordinates multiprotein complexes that mediate septation (10). An emerging model is that FtsE and FtsX form one such complex that senses the progress of cell division and regulates extracellular PG hydrolases (11,12). As expected for an integrated system, FtsE fails to localize to the divisome in the absence of FtsX (13).…”

“…In Escherichia coli, FtsX indirectly controls AmiA and AmiB PG amidase activity through an intervening scaffold protein, EnvC (11). A large extracellular domain (ECD) formed by the loop connecting the first two transmembrane helices in FtsX interacts with EnvC at the N terminus.…”

“…FtsEX shows homology to ABC transporters (14,15). FtsE, a predicted ATP binding cassette, requires wild-type Walker motifs for function, implicating ATP turnover in signaling (11). FtsE links the Z ring to the transmembrane protein, FtsX.…”