Faculty

Many biological processes are carried out by complex, multi-component macromolecular assemblies.  The assembly and dynamics of these molecular machines has been central to structural and cell biology, and has imposed tremendous challenges owing to their unusual complexity.  The research in this lab aims to understand the structural basis of assembly, dynamics and function of molecular complexes by using X-ray crystallography and electron cryo-microscopy as primary techniques.  The current research is focused on viruses and bacterial infectosome.

DNA packaging/translocation is crucial in assembly and infection of many double-stranded DNA (dsDNA) viruses such as bacteriophages T7 and P22 and herpesvirus.  The DNA packaging is achieved at a unique vertex of the viral capsid by a molecular motor consisting of the portal and terminase complex, which cleaves monomeric units from concatemeric viral DNA and pumps DNA into the capsid in an ATP-dependent manner.  The translocation of viral DNA from within the capsid into the host cell in bacteriophages such as T7 and P22 involves a series of precisely controlled molecular events, fulfilled by several virally encoded proteins.  The molecular mechanisms of DNA packaging and translocation in dsDNA bacteriophage and herpesvirus are being investigated by means of X-ray crystallography and electron cryo-microscopy.

Many Gram-negative pathogenic bacteria employ a complex protein secretion system termed type III secretion system (TTSS) to transport bacterial effector proteins across three membrane barriers into eukaryotic host cytoplasm.  The effector proteins delivered by TTSS are capable of modulating and interfering with the host cellular processes, which cause diseases in animals and plants such as plague, typhoid fever, bacterial dysentery.  The TTSS is composed of more than 20 structural proteins, effector proteins, and chaperones.  Our structural investigation targets the major structural components, the needle complex and the translocon, of TTSS in Shigella flexneri.

Representative Publications

• Liang Tang, Eddie B. Gilcrease, Sherwood Casjens, John E. Johnson (2006) Highly discriminatory binding of capsid cementing proteins in bacteriophage L. Structure 14, 837-45.
• Gabriel C. Lander, Liang Tang, Sherwood R. Casjens, Eddie B. Gilcrease, Peter Prevelige, Anton Poliakov, Clinton S. Potter, Bridget Carragher and John E. Johnson. (2006) The structure of an infectious p22 virion shows the signal for headful DNA packaging. Science 312, 1791-5. Epub 2006 May 18. [Featured on the cover]
• Reza Khayat, Liang Tang, Mark Young, John E. Johnson (2005) Structure of an archaeal virus capsid protein reveals a common ancestry to eukaryotic and bacterial viruses. Proc. Natl. Acad. Sci. USA. 102, 18944-9.
• L. Tang, W. Marion, G. Cingolani, P.E. Prevelige & J.E. Johnson (2005) The three-dimensional structure of the bacteriophage P22 tail machine. EMBO J. 24, 2087-95. [cover story]
• G. Rice, L. Tang, K. Stedman, F. Roberto, J. Spuhler, E. Gillitzer, J.E. Johnson, T. Douglas, and M.J. Young (2004) The structure of a thermophilic archaeal virus shows a dsDNA viral capsid type that spans all domains of life. Proc. Natl. Acad. Sci. USA101, 7716-7720.
• L. Tang, C.-S. Lin, N.K. Krishna, M. Yeager, A. Schneemann & J.E. Johnson (2002) Virus-like particles of a fish nodavirus display a capsid subunit domain organization different from that of insect nodaviruses. Journal of Virology 76, 6370–6375.
• L. Tang & J.E. Johnson (2002) Structural biology of viruses by the combination of electron cryomicroscopy and X-ray crystallography. Biochemistry 41, 11517-11524.
• L. Tang, K.N. Johnson, L.A. Ball, T. Lin, M. Yeager & J.E. Johnson (2001) The structure of Pariacoto virus reveals a dodecahedral cage of duplex RNA. Nature Structural Biology8, 77-83.