Many organisms have homologous type IV secretion systems, including the pathogens Agrobacterium tumefaciens C58 (VirB), Helicobacter pylori (CAG; ComB), Pseudomonas aeruginosa (TraS/TraB), Bordetella pertussis (Ptl), E. coli (Tra), Legionella pneumophila (Dot) [25] and the nitrogen-fixing plant mutualist Mesorhizobium

loti [26]. While these systems may share functional similarities, not all systems contain the same sets of genes [27]. The only common protein is VirB10 (TrbI) among all characterized systems [17]. Although type IV secretion systems have garnered attention because of roles in pathogenesis, it is important to point out that not all bacteria have a T4SS. Agrobacterium tumefaciens C58 has been the model system for Selonsertib price studying the T4SS. The VirB system from A. tumefaciens C58 is capable of exporting DNA-protein complex from its Ti plasmid into the host [25]. The main virulence mechanism is to inject T-DNA into the host to cause cancerous growth or the formation Tucidinostat in vitro of crown gall tumors, which then produce opines as carbon and energy sources for the pathogen. The major components of the T4SS in A. tumefaciens C58 are VirB2-VirB11 and VirD4. VirB1 is responsible for the remodeling of the peptidoglycan via the activity of lytic transglycosylase. The majority

of the VirB proteins are responsible for forming the structure complex of the secretory machinery, which is powered by the hydrolysis of ATP. Type V secretion system There are three sub-classes of the type V secretion machinery (T5SS). The archetypal bacterial proteins secreted via the T5SS (and dubbed the T5aSS sub-class) consist of an N-terminal passenger domain from 40 Kd to 400 Kd in size and a conserved C-terminal domain, which forms a beta barrel (reviewed in [28–31]). The proteins are synthesized with an N-terminal signal peptide that directs their export into the periplasm via the Sec machinery. The beta barrel can insert into the outer membrane and is required for translocation of the passenger domain into the extracellular space. In some cases, such as adhesins, the passenger domain remains attached to the beta barrel and the protein remains anchored in the outer

membrane. Cyclin-dependent kinase 3 In other cases, the passenger domain is cleaved from the beta barrel and forms a soluble hydrolytic enzyme or toxin. These proteins have been called auto-transporters because the C-terminal domains form a beta barrel with the potential to form a pore through which the N-terminal domain could pass [28–31]. More recent TEW-7197 price detailed structural studies however suggest that the barrel is incapable of transporting the passenger domain by itself [30]. A helper protein, perhaps Omp85/YaeT, has been hypothesized to facilitate translocation across the outer membrane [30]. A second sub-class of proteins secreted via the T5SS process, dubbed T5cSS proteins, are trimeric proteins in which a single beta barrel is formed by contributions from all three polypeptides.

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