THE TOLB PROTEIN INTERACTS WITH THE PORINS OF ESCHERICHIA-COLI

TolB is a periplasmic protein of the cell envelope Tol complex. It is partially membrane associated through an interaction with the outer me mbrane lipoprotein PAL (peptidoglycan-associated lipoprotein), which a lso belongs to the Tol system. The interaction of TolB with outer memb rane porins of Escherichia coli was investigated with a purified TolB derivative harboring a six-histidine tag. TolB interacted with the tri meric porins OmpF, OmpC, PhoE, and LamB but not with their denatured m onomeric forms or OmpA. These interactions took place both in the pres ence and in the absence of lipopolysaccharide. TolA, an inner membrane component of the Tol system, also interacts with the trimeric porins via its central periplasmic domain (R. Derouiche, M. Gavioli, H. Bened etti, A. Prilipov, G. Lazdlunski, and R. Lloubes, EMBO J. 15:6408-6415 , 1996). In the presence of the purified central domain of TolA (TolAI IHis), the TolB-porin complexes disappeared to form TolAIIHis-porin co mplexes. These results suggest that the interactions of TolA and TolB with porins might take place in vivo and might be concomitant events p articipating in porin assembly. They also suggest that the Tol system as a whole map be involved in porin assembly in the outer membrane.