PEPTIDOGLYCAN-ASSOCIATED LIPOPROTEIN-TOLB INTERACTION

TolA, B, -Q, and -R proteins are involved in maintaining the cell enve lope integrity of Escherichia coli; they have been parasitized by the group A colicins and the single strand DNA of some filamentous bacteri ophages to permit them to enter the cells, TolA and TolR are anchored to the inner membrane by a single transmembrane domain, TolQ is an int egral membrane protein with three transmembrane segments, and TolB has re cently been found to be periplasmic although it is partially membr ane-associated The latter result suggests that TolB might interact wit h membrane proteins, Other lines of evidence favor the existence of a Tol complex, To further characterize this complex, we investigated whi ch proteins interact with TolB, For this purpose, two different method s were used, First, we took advantage of the existence of a tagged Tol B (TolBep) to perform immunoprecipitation under native conditions in o rder to preserve the putative associations of TolBep with other protei ns, Secondly, in vivo cross-linking experiments with formaldehyde were performed, These two approaches led to the same result and demonstrat ed for the first time that a component of the Tol system, TolB, intera cts with a protein located in the outer membrane, the peptidoglycan-as sociated lipoprotein.