TOLB PROTEIN OF ESCHERICHIA-COLI K-12 INTERACTS WITH THE OUTER-MEMBRANE PEPTIDOGLYCAN-ASSOCIATED PROTEINS PAL, LPP AND OMPA

The Tol-Pal proteins of Escherichia coli are involved in maintaining o uter membrane integrity. Transmembrane domains of TolQ, TolR and TolA interact in the cytoplasmic membrane, while TolB and Pal form a comple x near the outer membrane. TolB and the central domain of TolA interac t in vitro with the outer membrane porins. In this study, both genetic and biochemical analyses were carried out to analyse the links betwee n TolB, Pal and other components of the cell envelope. It was shown th at TolB could be cross-linked in vivo with Pal, OmpA and Lpp, while Pa l was associated with TolB and OmpA. The isolation of pal and tolB mut ants disrupting some interactions between these proteins represents a first approach to characterizing the residues contributing to the inte ractions. We propose that TolB and Pal are part of a multiprotein comp lex that links the peptidoglycan to the outer membrane. The Tol-Pal pr oteins might form trans-envelope complexes that bring the two membrane s into close proximity and help some outer membrane components to reac h their final destination.