A NOVEL DNAJ-LIKE PROTEIN IN ESCHERICHIA-COLI INSERTS INTO THE CYTOPLASMIC MEMBRANE WITH A TYPE-III TOPOLOGY

We describe a novel Escherichia coil protein, DjlA, containing a highl y conserved J-region motif, which is present in the DnaJ protein chape rone family and required for interaction with DnaK, Remarkably, DjlA i s shown to be a membrane protein, localized to the inner membrane with the unusual Type III topology (N-out, C-in), Thus, DjlA appears to pr esent an extremely short N-terminus to the periplasm and has a single transmembrane domain (TMD) and a large cytoplasmic domain containing t he C-terminal J-region. Analysis of the TMD of DjlA and recently ident ified homologues in Coxiella burnetti and Haemophilus influenzae revea led a striking pattern of conserved glycines (or rarely alanine), with a four-residue spacing, This motif, predicted to form a spiral groove in the TMD, is more marked than a repeating glycine motif, implicated in the dimerization of TMDs of some eukaryotic proteins, This feature of DjlA could represent a promiscuous docking mechanism for interacti on with a variety of membrane proteins, DjlA null mutants can be isola ted but these appear rapidly to accumulate suppressors to correct enve lope and growth defects, Moderate (10-fold) overproduction of DjlA sup presses a mutation in FtsZ but markedly perturbs cell division and cel l-envelope growth in minimal medium. We propose that DjlA plays a role in the correct assembly, activity and/or maintenance of a number of m embrane proteins, including two-component signal-transduction systems.