PhD ceremony Ms. V.J. Goosens: Bacillus systems exporting folded proteins and folding exported proteins

PhD ceremony: Ms. V.J. Goosens

Dissertation: Bacillus systems exporting folded proteins and folding exported proteins

Promotor(s): prof. J.M. van Dijl

Faculty: Medical Sciences

Protein translocation across a membrane is an essential component of many cellular functions in all kingdoms of life. However, simply moving a protein over the membrane does not guarantee an operational protein - functional proteins need to be correctly folded and occasionally require co-factors. Bacillus subtilis, the model organism used to examine protein translocation in this study, is a Gram-positive bacterium relevant in both application-oriented and fundamental scientific settings. The research described in this thesis was focused on systems either involved in the membrane translocation of cargo proteins where folding and co-factor-attachment takes place prior to translocation, or involved in the post-translocational folding of proteins that are translocated in an unfolded state. These systems are known as the Twin-arginine translocation (Tat) and Thiol-disulphide oxidoreductase (TDOR) pathways, respectively. In the studies presented here, mass spectrometric techniques were firstly applied, and by observing the presence of proteins in various genetic backgrounds novel interacting partners and substrates were identified in both the Tat and the TDOR systems. The newly identified Tat-dependent substrate QcrA was investigated further, and by mutating residues associated with folding and co-factor insertion, requirements for QcrA-Tat processing were identified. The Tat system is made up of TatA and TatC proteins, and in this thesis a role for the third, and until recently enigmatic, TatA component TatAc was unveiled. Therefore, the research presented in this thesis led to novel insights into the processing, substrates and systems associated with the translocation of folded proteins (Tat) and folding of proteins post-translocation (TDOR).