Esther S. Axelrod Bullitt, Ph.D.

Some Details of Bacterial Adhesion Research

Escherichia coli (E. coli) cause 70-95% of community-acquired UTIs and about 50% of hospital-acquired infections. The presence of surface filaments, called bacterial adhesion pili, are necessary for binding to the host uroepithelial cells. In particular, P pili are necessary for E. coli that cause UTIs involving the kidneys (pyelonephritis), and Type 1 pili are necessary for bladder infections due to cystitis-causing E. coli. A three-dimensional helical reconstruction of P pili (right) reveals a filament with 3.28 subunits per turn of the helix, and a rise of 7.58A per subunit. The filament is 68A in diameter and ~1um in length. It has an ellipsoidal central cavity 25Ax15A that winds about the helical axis, and connects with radial holes that extend to the surface of the pili.
Isolated pili are often damaged (image below), though sometimes these structures remain tethered to intact segments of pilus. As long as the pilus remains intact, albeit damaged, it can serve its only function: it can maintain attachment between the bacterium and its host cell. Our current model for P pili (bottom of this webpage) is a structure that can overextend its helix by a factor of five to withstand the shear forces present in its native environment, the human urinary tract.

3D Helical Reconstruction

The helical reconstruction computer programs are based on programs originally developed at the Medical Research Council Laboratory for Molecular Biology, Cambridge, England (DeRosier and Moore, 1970 ; Amos, 1975 ). Briefly, the helical reconstruction procedure includes:

• filament selection; relatively straight, low background, not overlapping other pili

• straightening with a cubic splinefit -compute Fast Fourier transform

• collect data along the layerlines defined by the helical symmetry

• locate phase origin, out-of-plane tilt, and polarity of the filaments

• average data from all filaments; use an amplitude-weighted phase residual for fitting

• compute Fourier-Bessel transform of each F(R,0,l/c)exp(+/-inp/2) and expand to compute the density at all points in three dimensions

• view the results as surface structures and cross-sections of the helical axis

As more bacteria become resistant to antibiotics, it is essential to find novel approaches for prevention and treatment of infection. Understanding the structure of adhesion pili provides information needed for discovering ways to prevent the binding of these pathogens, or to remove bound bacteria.

Amos, L.A. (1975). Combination of data from helical particles: correlation and selection. J. Mol. Biol. 99:65-73.

Bullitt, E. and L. Makowski (1998). Bacterial adhesion pili are heterologous assemblies of similar subunits.
Biophys J 74(1):623-32.

Bullitt, E., C.H. Jones, R. Striker, G. Soto, F. Jacob-Dubuisson, J. Pinkner, M.J. Wick, L. Makowski, and S.J. Hultgren (1996). Development of pilus organelle subassemblies in vitro depends on chaperone uncapping of a beta zipper. Proc Natl Acad Sci USA 93(23):12890-5.

Bullitt, E. and L. Makowski (1995). Structural polymorphism of bacterial adhesion pili. Nature 373:164-167.

DeRosier, D.J. and P.B. Moore. (1970). Reconstruction of three-dimensional images from electron micrographs of structures with helical symmetry. J. Mol. Biol. 52:355-369.

Mu XQ, E.H. Egelman, E. Bullitt. (2002). Structure and Function of Hib Pili from Haemophilus influenzae Type b.
J Bacteriol. 184(17):4868-4874

St. Geme, J.W., J.S. Pinkner 3rd, G.P. Krasan, J. Heuser, E. Bullitt, A.L. Smith, and S.J. Hultgren (1996). Haemophilus influenzae pili are composite structures assembled via the HifB chaperone. Proc Natl Acad Sci USA 93(21):11913-8.