Research Group
| SA Associate Professor | Tomoko Kubori |
Research Projects
Protein secretion is a process of fundamental importance for bacterial pathogenesis. Whether they deliver toxins or directly inject effector proteins into the cytoplasm of host cells, bacterial protein secretion systems play a central role in modulating eukaryotic cell functions. Legionella pneumophila are Gram-negative bacteria that are found ubiquitously in soil and freshwater environments. Once inhaled by humans, Legionella infections can result in a severe form of pneumonia known as Legionnaires’ disease. Legionella use a type IV secretion system (T4SS) to deliver effector proteins, which mediates the establishment of a replicative niche in host cells.
The goal of our research is to understand, at the molecular level, how Legionella subverts host cellular functions to accomplish successful intracellular replication. To this end, the following research projects are currently in progress.
The goal of our research is to understand, at the molecular level, how Legionella subverts host cellular functions to accomplish successful intracellular replication. To this end, the following research projects are currently in progress.
(1) Analysis of the structure and function of the type IV secretion apparatus.
Essentially nothing is known about the substrate transfer across eukaryotic and bacterial membranes that occurs via type IV secretion systems. Furthermore, the macromolecular structure of the type IV secretion apparatus is largely unknown. To address these questions, we are analyzing the structure and function of the type IV secretion apparatus of Legionella.
Essentially nothing is known about the substrate transfer across eukaryotic and bacterial membranes that occurs via type IV secretion systems. Furthermore, the macromolecular structure of the type IV secretion apparatus is largely unknown. To address these questions, we are analyzing the structure and function of the type IV secretion apparatus of Legionella.
Fig. 1. T4SS core component DotD represents a conserved structural motif of the periplasmic ring.
(2) Analysis of effector proteins that translocate from Legionella to host cells.
We previously demonstrated that RalF is translocated by the type IV secretion system of Legionella into host cells and is required for the recruitment of host ARF proteins to Legionella-containing vacuoles. We also recently demonstrated that the effector LubX acts as an E3 ligase and targets another effector for proteasomal degradation within host cells. LubX is the first effector protein that has been shown to target and regulate another effector within host cells.
We previously demonstrated that RalF is translocated by the type IV secretion system of Legionella into host cells and is required for the recruitment of host ARF proteins to Legionella-containing vacuoles. We also recently demonstrated that the effector LubX acts as an E3 ligase and targets another effector for proteasomal degradation within host cells. LubX is the first effector protein that has been shown to target and regulate another effector within host cells.
Fig. 2 Discovery of metaeffector.
(3) Interaction of Legionella and its natural hosts.
The ability of Legionella to survive and replicate within eukaryotic cells has been acquired during its history of interactions with natural hosts such as free-living amoebae. Taking advantage of the recent development of the NGS technique, we are analyzing the molecular interactions between amoebae and amoeba symbionts/pathogens, including Legionella.
The ability of Legionella to survive and replicate within eukaryotic cells has been acquired during its history of interactions with natural hosts such as free-living amoebae. Taking advantage of the recent development of the NGS technique, we are analyzing the molecular interactions between amoebae and amoeba symbionts/pathogens, including Legionella.
Major publications
- Hubber A, Kubori T, *Nagai H. Modulation of the ubiquitination machinery by Legionella. Curr Top Microbiol Immunol. 2014:376, 227-247
- Hori JI, Pereira MS, Roy CR, *Nagai H, Zamboni DS. Identification and functional characterization of K(+) transporters encoded by Legionella pneumophila kup genes. Cell Microbiol. 2013: 15, 2006-2019
- Nagai H and Kubori T. Dot/Icm type IVB secretion systems of Legionella and other gram-negative bacteria. Front Microbiol. 2011: 2,136.
- Kubori T, Shinzawa N, Kanuka H, Nagai H. Legionella metaeffector exploits host proteasome to temporally regulate cognate effector. PLoS Pathog. 2010;6(12),e1001216.
- Nakano N, Kubori T, Kinoshita M, Imada K, Nagai H. Crystal structure of Legionella DotD: insights into the relationship between type IVB and type II/III secretion systems. PLoS Pathog. 2010;6(10),e1001129.
Links
- Laboratory of Combined Research on Microbiology and Immunology