Debnath Ghosal (CalTech)

Debnath Ghosal (CalTech)

Special Seminar

Event Date/Location

January 22, 2019 -
12:00 pm to 1:00 pm
Schultz Laboratory 107


  • Debnath Ghosal (CalTech)

    California Institute of Technology


In Situ Structures of the Bacterial Type IV Secretion System by Electron Cryotomography

Type IV secretion systems (T4SSs) are large macromolecular machines that translocate protein and DNA and are involved in the pathogenesis of multiple human diseases. We used complementary electron cryotomography and immunofluorescence microscopy to investigate the molecular architecture and biogenesis of the Dot/Icm type IVB secretion system (T4BSS) utilized by the human pathogen Legionella pneumophila. Our detailed structural analysis mapped the location of the core and accessory components of the Legionella core-transmembrane subcomplex revealing a well-ordered central channel that opens into a windowed large secretion chamber with an unusual symmetry. Exploiting these findings, we deciphered an early-stage assembly process that begins with targeting of Dot/Icm components to the bacterial poles. Polar targeting of this T4BSS is mediated by two Dot/Icm proteins, DotU and IcmF, that interestingly are homologs of the T6SS membrane complex components TssL and TssM, suggesting the Dot/Icm T4BSS is a hybrid system. Finally, in depth examination of the biogenesis pathway revealed that the Dot/Icm complex assembles by an innovative “outside-inside” mechanism.


Free and open to the university community and the public.


Nieng Yan, Department of Molecular Biology