Our group is interested in the evolution of intracellular bacteria into genetically integrated organelles. As a model system we use the cercozoan amoeba Paulinella chromatophora which contains early-evolutionary-state photosynthetic organelles, called chromatophores. Genomic analyses demonstrated that functions encoded on chromatophore and nuclear genome are highly complementary. Mass spectrometric analyses of the chromatophore proteome revealed the import of hundreds of nucleus-encoded proteins into the chromatophore. Interestingly, imported proteins fall into two classes: long import candidates (>260 amino acids (aa)) and short import candidates (<90 aa). Long import candidates carry a conserved ~200 aa long N-terminal sequence extension that apparently marks these proteins for the import into the chromatophore. Many short import candidates seem to have properties of antimicrobial peptides. The mechanisms underlying protein import into the chromatophore remain elusive.

The main aims of this project are to determine the molecular mechanisms that underpin this novel type of protein translocation across the chromatophore envelope membranes and to characterize ultrastructure and lipid composition of this membrane system. This work will include structural analyses of crTPs and chromatophore-targeted antimicrobial peptides, establishment of in vitro import assays, the determination of proteinaceous interaction patners of the crTP, and protein-lipid interaction assays.