The LIU LAB
Electron Tomography at Yale University
Visualization of Bacterial Type III Secretion System
Gram-negative bacteria secrete a wide range of proteins, nutrient acquisition, virulence, and efflux of drugs and other toxins. Among those secretion systems, the Type III secretion systems (T3SS) are essential virulence determinants for many Gram-negative pathogens. The injectisome, also known as the needle complex, is the central T3SS machine required to inject effector proteins from the bacterium into eukaryotic host cells. To achieve high-resolution structures of intact injectisomes, we genetically engineered minicells that are significantly smaller than normal bacterial cells. We used high-throughput cryo-ET to determine 3D structures of intact injectisomes and reveal the cytoplasmic sorting platform essential for substrate recruitment and translocation (Hu, et al., PNAS 2015; Hu, et al., Cell 2017; Park, et al., Elife 2018; Butan et al., PNAS 2019).
Chemoreceptor Array Formation
The Flagellar Structure and Assembly in the Lyme Disease Spirochete
Spirochetes are a medically important group of bacteria with a distinct morphology. Many spirochetes, including Treponema, Borrelia, and Leptospira, are highly motile and invasive pathogens. Periplasmic flagella are the main organelles for the unique spirochete motility. Our long-term goal is to understand the structural basis of flagellar assembly and rotation in spirochetes at the molecular level. This project is supported by NIH/NIAID.
Chemoreceptor Array
References
· Liu J, Hu B, Morado DR, Jani S, Manson MD, Margolin W: Molecular architecture of chemoreceptor arrays revealed by cryoelectron tomography of Escherichia coli minicells, Proc Natl Acad Sci U S A 109(23):E1481-8, 2012.
· Liu J, Lin T, Botkin DJ, McCrum E, Winkler H, Norris SJ: Intact Flagellar Motor of Borrelia burgdorferi Revealed by Cryo-Electron Tomography: Evidence for Stator Ring Curvature and Rotor/C Ring Assembly Flexion, J Bacteriol 191(16):5026-36, 2009.
· Zhao X, Zhang K, Boquoi T, Hu B, Motaleb MA, Miller K, James M, Charon NW, Manson MD, Norris SJ, Li C, Liu J: Cryo-Electron Tomography Reveals the Sequential Assembly of Bacterial Flagella in Borrelia burgdorferi, Proc Natl Acad Sci U S A, 110(35): 14390-5.
. Zhao X, Norris SJ, Liu J: Molecular Architecture of Bacterial Flagellar Motor in Cells. Biochemistry. 2014 Apr 3. [Epub ahead of print]
. Hu B, Morado DR, Margolin W, Rohde JR, Arizmendi O, Picking WL, Picking WD, Liu J: Visualization of the type III secretion sorting platform of Shigella flexneri. Proc Natl Acad Sci U S A. 2015 Jan 12.
Bacterial Motility and Chemotaxis
Bacterial chemotaxis is the phenomenon in which bacteria are constantly sensing their environment and adjusting their behavior accordingly to grow and survive. Bacterial chemotaxis/motility pathway has been studied extensively, and has become the pre-eminent model system for understanding the mechanisms underlying transmembrane signaling, motility and cellular behavior. We genetically engineered tiny E. coli minicell as a model system to determine structures of the receptor arrays and motor complexes in cellular context. Our on-going project is support by NIH/NIGMS.