A novel DnaJ‐like protein in Escherichia coli inserts into the cytoplasmic membrane with a Type III topology

Abstract

We describe a novel Escherichia coli protein, DjlA, containing a highly conserved J‐region motif, which is present in the DnaJ protein chaperone family and required for interaction with DnaK. Remarkably, DjlA is 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 present an extremely short N‐terminus to the periplasm and has a single transmembrane domain (TMD) and a large cytoplasmic domain containing the C‐terminal J‐region. Analysis of the TMD of DjIA and recently identified homologues in Coxiella burnetti and Haemophilus influenzae revealed 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 interaction with a variety of membrane proteins. DjlA null mutants can be isolated but these appear rapidly to accumulate suppressors to correct envelope and growth defects. Moderate (10‐fold) overproduction of DjlA suppresses a mutation in FtsZ but markedly perturbs cell division and cell‐envelope growth in minimal medium. We propose that DjlA plays a role in the correct assembly, activity and/or maintenance of a number of membrane proteins, including two‐component signal‐transduction systems.