Regulation of outer membrane biogenesis components LptD and Omp85 in cyanobacteria Anabaena sp. PCC 7120

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Cyanobacteria are photoautotrophic bacteria surrounded by an outer membrane in addition to the plasma membrane and the peptidoglycan layer. The biogenesis of this highly functional membrane is a complex phenomenon involving distinct machineries for the assembly of the outer membrane specific lipids and outer membrane proteins. The major outer membrane localized factors involved in this process are proteins of the polypeptide-transporting beta-barrel family and proteins for lipid A export. Both protein families found in cyanobacteria are phylogenetically related to the respective machineries involved in chloroplast biogenesis. We aim to understand the function and the interplay of these essential factors for outer membrane biogenesis in the cyanobacterium Anabaena sp. PCC 7120 as a cyanobacterial model system. We will explore the functional diversity of the three identified Omp85 proteins. This includes substrate definition as well as the analysis of the complexes formed by these three proteins. In parallel, we will analyze the complex architecture of the lipid A transport system as well as the functional mode of the transfer of the lipid molecule across the periplasm. The results will yield an understanding of the functional mode of the outer membrane, which is important for cell survival as it forms the outer barrier to the environment. In addition, our results will allow conclusions on the function of the proteins in chloroplasts, which contain both protein families in their outer membrane with function in protein and lipid transport.