Esther Bullitt, Ph.D.
|Associate Professor of Physiology & Biophysics
A.B. Grinnell College
|Phone: (617) 358-8464
Fax: (617) 358-8804
Address: see below
Link to BU Faculty Profile
Link to ORCID
Protein Structure Facilitates Function
Using Electron Microscopy and Quantitative Image Analysis to see how Macromolecular Assemblies Work
Structural studies of biological macromolecular assemblies are providing a deeper understanding of cellular function. In our laboratory, we utilize electron microscopy and image reconstruction to investigate questions about:
- how adhesion pili aid pathogenic bacterial survival
- how viruses impact cellular processes
- how the type III secretion system is assembled, leading to secretion of toxins
BACTERIAL ADHESION PILI
YouTube: the role of basic research in developing a vaccine against Traveler’s Diarrhea: Vaccine from basic research
Fibers on the surfaces of many pathogenic bacteria can overextend like a toy Slinky, whereas homologous proteins on bacteria that cause pneumonia, ear infections, and meningitis assemble into a 3-stranded rope-like fibers (blue). In collaboration with Dr. Magnus Andersson’s lab at Umeå University in Umeå Sweden we have shown that the forces required for unwinding pili (also called ‘fimbriae’) are specific for the pilus-type, and thus vary with the microenvironment expected to be encountered. For example, CFA/I pili on diarrhea-causing intestinal bacteria unwind at less than one-third the force required to unwind P-pili expressed on urinary tract infection bacteria.
Our electron cryomicroscopy results now show the structure of CFA/I pili at 4.3 A resolution. Published in
IUCrJ (2019). 6, 815–821,
As more bacteria become resistant to antibiotics, it is essential to develop novel approaches for prevention and treatment of infection. Structural studies are vital for discovering clues to how bacteria bind, and how they remain attached while the host is trying to remove them. We are examining the architecture of bacterial adhesion pili and investigating small molecules that disrupt their assembly and/or function. We see that pilin subunits must rotate to form a helical filament, after exiting linearly from the bacterial surface.
TYPE III SECRETION
Only 10 bacteria (or fewer!) are needed for Shigella flexneri to cause dysentery (bloody diarrhea). This disease is initiated via the type III secretion system, which is used to secrete both toxins and bacterial effectors that alter normal host cell functions to promote bacterial growth and spread.
To understand (and disrupt) the process of infection, we are examining assembly intermediates of the T3SS syringe-like needle and its tip structure. Through our collaborations with the Picking lab at Oklahoma State University Stillwater and the Geisbrecht lab at the University of Missouri Kansas City we have shown that IpaD, the first protein that localizes to the needle tip, is present as a pentamer, and undergoes a dramatic conformational change as compared to the structure that has been solved by x-ray crystallography.
The structures of three-dimensional reconstructions of immature and nascent needle tips show clearly IpaD as an elongated pentameric structure.
This new result demonstrates that the distal domain of IpaD flips up, as compared to the structure solved by X-ray crystallography (pdb 2j0o).
Diagram to the right shows the conformational change of the distal domain that is needed to fit the crystal structure of IpaD into our density map of 3-dimensional reconstructions from electron microscopy data.
The poliovirus polymerase, 3Dpol, is an RNA-dependent RNA polymerase. Its structure is similar to other polymerases, and can be described as a right hand. We are investigating the role of two-dimensional 3Dpol lattices in replication, using electron microscopy and image processing of tubes and sheets formed in vitro. The crystal structure shown was solved in Steve Schultz’s lab, pdb 1rdr.
In collaboration with Dr. Karla Kirkegaard’s lab at Stanford University we have shown that
1) 3Dpol forms two-dimensional lattices that we expect facilitate replication by concentrating substrate and enzyme onto a two-dimensional surface, the vesicular membrane,
2) “Zombie” 3Dpol protein (dead active site) can support assembly of oligomers and restore replication when the wild type protein concentration is too low to do so.
Zheng W, Andersson M, Mortezaei N, Bullitt E and Egelman E (2019). Cryo-EM structure of the CFA/I pilus rod. International Union of Crystallography J 6: 815–821.
Andersson M, Björnham O, Svantesson M, Badahdah A, Uhlin BE, Bullitt E. (2012). A Structural Basis for Sustained Bacterial Adhesion: Biomechanical Properties of CFA/I Pili., J Mol Biol. 2012 Feb 3;415(5):918-28.
Epler, C.R., N.E. Dickenson, E. Bullitt*, W.L. Picking* (2012). Ultrastructural analysis of IpaD at the tip of the nascent MxiH type III secretion apparatus of Shigella flexneri. J. Mol. Biol. 420:29-39. PMID: 22480614 *corresponding authors
Li, Y-F, S. Poole, K. Nishio, K. Jang, F. Rasulova, A. McVeigh, S.J. Savarino, D. Xia, E. Bullitt (2009). Structure of CFA/I fimbriae from enterotoxigenic Escherichia coli. Proc. Natl. Acad. Sci. 106:10793-10798.
Mu X.Q., S.J. Savarino, E. Bullitt (2008). The three-dimensional structurel of CFA/I adhesion pili: Traveler’s diarrhea bacteria hang on by a spring. J. Mol. Biol. 376:614-620.
Verger, D., E. Bullitt, S.J. Hultgren, G. Waksman (2007). Crystal structure of the P pilus rod subunit PapA. PLoS Pathogens 3:e73(674-682).
Mu XQ and E. Bullitt (2006). Structure and assembly of P-pili: a protruding hinge region used for assembly of a bacterial adhesion filament. Proc. Natl. Acad. Sci.103:9861-9866.
Mu X.Q., E.H. Egelman, E. Bullitt (2002). Structure and Function of Hib Pili from Haemophilus influenzae Type b. J Bacteriol. 184:4868-74.
Lyle J.M., E. Bullitt, K. Bienz, K. Kirkegaard (2002). Visualization and functional analysis of RNA-dependent RNA polymerase lattices. Science. Jun 21;296(5576):2218-22.
Bullitt E., M.P. Rout, J.V. Kilmartin, C.W. Akey(1997). The yeast spindle pole body is assembled around a central crystal of Spc42p. Cell Jun 27;89(7):1077-86.
Bullitt E, L. Makowski (1995). Structural polymorphism of bacterial adhesion pili. Nature Jan 12;373(6510):164-7.
Department of Physiology and Biophysics
Boston University School of Medicine
700 Albany Street
Boston MA 02118-2526
Phone: (617) 358-8464
Fax: (617) 358-8804