Our research activities
focus on the molecular mechanisms by which proteins are translocated across and integrated into cellular membranes. For this purpose, bacteria are outstanding model organisms. They possess an unrivalled diversity of distinct pathways for the export of cytosolically synthesized proteins into one of the layers of the bacterial cell envelope and into the surrounding medium. Furthermore, numerous virulence factors of pathogenic bacteria are secreted by one or the other of those export pathways.
Our central experimental approach
is to reproduce individual protein transport processes in cell-free systems making use of in vitro synthesized substrate proteins and isolated membrane vesicles. A particular objective is to develop and establish highly purified systems that consist of a minimal set of defined components only. To follow the path of a substrate protein across and into the lipid bilayer, we generate transport intermediates that allow identification of their reaction partners by methods such as site-specific cross-linking.
Topics of current research projects
The transport of folded proteins across cellular membranes is a major challenge to the maintenance of the membranes’ barrier function. Remarkably, in archaea, procaryotes, and plant chloroplasts the so-called Tat (twin-arginine translocation) system allows the transport for a group of folded proteins that carry a conserved twinarginine (RR-) motif in their signal sequences. Tat systems consist of the membrane proteins TatA, TatB, TatC and TatE, which assemble into higher order oligomeric structures on demand. We are elucidating the individual functions of TatABCE and the substrate-induced assembly processes.
Gram-negative bacteria use the type-V secretion pathway to expose proteins at their cell surface, many of which have virulence functions. Translocation of those proteins across the outer membrane occurs by means of specific β-barrels proteins, which require the β-barrel assembly machinery (BAM) for membrane integration. We are
studying details of these outer membrane-specific translocation and integration events using a newly established versatile in vitro reconstitution system.