Biological role of outer membrane vesicle-associated small proteins of the phytopathogen Agrobacterium tumefaciens

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Bacterial extracellular membrane vesicles are considered as novel players in various cell communication systems. Outer membrane vesicles (OMVs) are released from the outer membrane of many Gram-negative bacteria. The cargo of these extracellular nanostructures comprises distinct biomolecules such as small compounds, genetic material, proteins and peptides, which are involved in intra- and inter-species communication and pathogenicity.We have recently demonstrated that the phytopathogen Agrobacterium tumefaciens, the causative agent of crown gall disease, releases OMVs into the culture supernatant during growth. A proteome study of the OMV fractions obtained under different growth conditions identified about 60 proteins including the two conserved small proteins Atu2614 and Atu8019 with unknown functions. Both proteins contain a predicted N-terminal signal peptidase II sequence with a C-terminal consensus lipobox, a hallmark of lipoproteins. The mature form of Atu2614 is expected to contain 67 aa and comprises a highly hydrophobic domain with several extended glycine-zipper motifs commonly found in pore-forming membrane proteins. Atu8019 (mature size: 32 aa) shares sequence similarities to entericidin antidote/toxin peptides.In this proposal we aim at elucidating the biological roles of these two OMV-associated small proteins in Agrobacterium by combining genetic and biochemical approaches. With these studies we expect to obtain new valuable insights into the physiological relevance of OMV-associated small lipoproteins in bacteria.