An assay for protein-protein interaction mutant selection: Its application to the E. coli divisome components

FtsQ, an essential protein for the E. coli divisome assembly, is able to interact with various division proteins, namely FtsI, FtsL, FtsN, FtsB and FtsW. The FtsQ domains involved in these interactions were identified by two-hybrid assays (Di Lallo et al., 2003) and co-immunoprecipitation experiments. Progressive deletions of the ftsQ gene suggested that the FtsQ self-interaction and its interactions with the other proteins are localized in three periplasmic subdomains: (i) residues 50-135 constitute one of the sites involved in FtsQ, FtsI and FtsN interaction, and this site is also responsible for FtsW interaction; (ii) the FtsB interaction is localized between residues 136 and 202; and (iii) the FtsL interaction is localized at the very C-terminal extremity. In this third region, the interaction site for FtsK and also the second site for FtsQ, FtsI, FtsN interactions are located (D'Ulisse et al., 2007). A main problem to be solved in the protein-protein interaction studies is to determine their biological role. The behavior of interaction-defective mutants can furnish an answer to this question but the difficulty in the foreseen of these mutants phenotype makes this search very hard to perform. We have therefore developed an assay that allows selection of this kind of mutants leaving their phenotype out of consideration (Barbati et al., in preparation). The selection of FtsQ interaction mutants and the characterization of their phenotype will be described in the poster.