Biophysical Characterization of the FtsL/B Subcomplex of the Bacterial Divisom

Abstract

Cell division in the gram-negative bacterium Escherichia coli is carried out through the cooperative assembly of at least 10 required proteins, known as the divisome. Few divisome proteins have described functions, and the structural details of their interactions are still primitive. The focus of this study is the structural characterization of two proteins that interact independent of other divisome components; FtsL and FtsB. Both proteins contain a small cytoplasmic tail, a single-pass transmembrane domain (TMD), and a predicted coiled-coil domain (CCD). We are also structurally characterizing the homologs of FtsL and FtsB, FtsL and DivIC, respectively, in Bacillus subtilis, the gram-positive model system of bacteria.The sequences of FtsL and FtsB are not highly conserved, but similar proteins are present in other bacterial species. FtsL and FtsB rapidly degrade in the absence of one another in vivo, so their interaction is a possible regulation point in division. Additionally, the stability of FtsL and DivIC is predicted to be important for guarding against transmembrane proteolysis. Here, we present a detailed structural characterization done through the use of use of in vitro biophysical interaction assays, in vivo screening methods, and computational modeling. Due to the difficult nature of studying integral membrane proteins, we have dissected FtsL and FtsB into their separate domains and performed biophysical interaction assays to determine how the domains work together to interact in vitro. Our combinatorial approach will provide a basis for functional hypotheses of these proteins in vivo, significantly improving our understanding of bacterial cell division.