The Soluble Periplasmic Domains of Escherichia coli Cell Division Proteins FtsQ/FtsB/FtsL Form a Trimeric Complex with Submicromolar Affinity

• DOI: 10.1074/jbc.m115.654756
• Publication Date: 2015-07-10T03:05:17Z
• Authors: Marjolein Glas; H. Bart van den B...; Stephen H. McLaug...; Winfried Roseboom; Fan Liu; Gregory M. Koning...; Alexander Fish; Tanneke den Blaauwen; Albert J.R. Heck; Luitzen de Jong; Wilbert Bitter; Iwan J.P. de Esch; Joen Luirink
• Keywords: Models, Molecular; 0301 basic medicine; 570; Light; Molecular Sequence Data; Cell Cycle Proteins; Biosensing Techniques; Biochemistry; Mass Spectrometry; 03 medical and health sciences; Taverne; Escherichia coli; Amino Acid Sequence; Molecular Biology; 0303 health sciences; Escherichia coli Proteins; Membrane Proteins; Cell Biology; 3. Good health; Protein Structure, Tertiary; Molecular Weight; Protein Subunits; Cross-Linking Reagents; Immobilized Proteins; Multiprotein Complexes; Periplasm; Peptides; Cell Division; Protein Binding

Cell division in Escherichia coli involves a set of essential proteins that assembles at midcell to form the so-called divisome. The divisome regulates the invagination of the inner membrane, cell wall synthesis, and inward growth of the outer membrane. One of the divisome proteins, FtsQ, plays a central but enigmatic role in cell division. This protein associates with FtsB and FtsL, which, like FtsQ, are bitopic inner membrane proteins with a large periplasmic domain (denoted FtsQp, FtsBp, and FtsLp) that is indispensable for the function of each protein. Considering the vital nature and accessible location of the FtsQBL complex, it is an attractive target for protein-protein interaction inhibitors intended to block bacterial cell division. In this study, we expressed FtsQp, FtsBp, and FtsLp individually and in combination. Upon co-expression, FtsQp was co-purified with FtsBp and FtsLp from E. coli extracts as a stable trimeric complex. FtsBp was also shown to interact with FtsQp in the absence of FtsLp albeit with lower affinity. Interactions were mapped at the C terminus of the respective domains by site-specific cross-linking. The binding affinity and 1:1:1 stoichiometry of the FtsQpBpLp complex and the FtsQpBp subcomplex were determined in complementary surface plasmon resonance, analytical ultracentrifugation, and native mass spectrometry experiments.