ACKNOWLEDGMENTS
This work was supported by Wellcome Trust grants 098302 to G.W. and
093228 to T.K.S. and NIH grant GM035269 to E.H.E. We thank Natasha
Lukoyanova for help during data collection and Laura S. Frost for fruitful
discussions.
Received: May 10, 2016
Revised: July 4, 2016
Accepted: August 11, 2016
Published: September 8, 2016
REFERENCES
Adams, P.D., Afonine, P.V., Bunko ́czi, G., Chen, V.B., Davis, I.W., Echols, N.,
Headd, J.J., Hung, L.W., Kapral, G.J., Grosse-Kunstleve, R.W., et al. (2010).
PHENIX: a comprehensive Python-based system for macromolecular struc-
ture solution. Acta Crystallogr. D Biol. Crystallogr. 66 , 213–221.
Arutyunov, D., and Frost, L.S. (2013). F conjugation: back to the beginning.
Plasmid 70 , 18–32.
Babic, A., Lindner, A.B., Vulic, M., Stewart, E.J., and Radman, M. (2008). Direct
visualization of horizontal gene transfer. Science 319 , 1533–1536.
Caro, L.G., and Schno ̈s, M. (1966). The attachment of the male-specific bacte-
riophage F1 to sensitive strains ofEscherichia coli. Proc. Natl. Acad. Sci. USA
56 , 126–132.
Chen, V.B., Arendall, W.B., 3rd, Headd, J.J., Keedy, D.A., Immormino, R.M.,
Kapral, G.J., Murray, L.W., Richardson, J.S., and Richardson, D.C. (2010).
MolProbity: all-atom structure validation for macromolecular crystallography.
Acta Crystallogr. D Biol. Crystallogr. 66 , 12–21.
Clarke, M., Maddera, L., Harris, R.L., and Silverman, P.M. (2008). F-pili dy-
namics by live-cell imaging. Proc. Natl. Acad. Sci. USA 105 , 17978–17981.
Costa, T.R., Felisberto-Rodrigues, C., Meir, A., Prevost, M.S., Redzej, A.,
Trokter, M., and Waksman, G. (2015). Secretion systems in Gram-negative
bacteria: structural and mechanistic insights. Nat. Rev. Microbiol. 13 ,
343–359.
Crawford, E.M., and Gesteland, R.F. (1964). The adsorption of bacteriophage
R17. Virology 22 , 165–167.
Debreczeni, J.E., and Emsley, P. (2012). Handling ligands with Coot. Acta
Crystallogr. D Biol. Crystallogr. 68 , 425–430.
Egelman, E.H. (2000). A robust algorithm for the reconstruction of helical fila-
ments using single-particle methods. Ultramicroscopy 85 , 225–234.
Egelman, E.H. (2014). Ambiguities in helical reconstruction. eLife 3 , e04969.
Emsley, P., Lohkamp, B., Scott, W.G., and Cowtan, K. (2010). Features and
development of Coot. Acta Crystallogr. D Biol. Crystallogr. 66 , 486–501.
Folkhard, W., Leonard, K.R., Malsey, S., Marvin, D.A., Dubochet, J., Engel, A.,
Achtman, M., and Helmuth, R. (1979). X-ray diffraction and electron micro-
scope studies on the structure of bacterial F pili. J. Mol. Biol. 130 , 145–160.
Frank, J., Radermacher, M., Penczek, P., Zhu, J., Li, Y., Ladjadj, M., and Leith,
A. (1996). SPIDER and WEB: processing and visualization of images in 3D
electron microscopy and related fields. J. Struct. Biol. 116 , 190–199.
Fronzes, R., Scha ̈fer, E., Wang, L., Saibil, H.R., Orlova, E.V., and Waksman, G.
(2009). Structure of a type IV secretion system core complex. Science 323 ,
266–268.
Frost, L.S., and Paranchych, W. (1988). DNA sequence analysis of point muta-
tions in traA, the F pilin gene, reveal two domains involved in F-specific bacte-
riophage attachment. Mol. Gen. Genet. 213 , 134–139.
Fyffe, S.A., Alphey, M.S., Buetow, L., Smith, T.K., Ferguson, M.A., Sørensen,
M.D., Bjo ̈rkling, F., and Hunter, W.N. (2006). Reevaluation of the PPAR-beta/
delta ligand binding domain model reveals why it exhibits the activated form.
Mol. Cell 21 , 1–2.
Ilangovan, A., Connery, S., and Waksman, G. (2015). Structural biology of the
Gram-negative bacterial conjugation systems. Trends Microbiol. 23 , 301–310.
Kabsch, W. (1976). A solution for the best rotation to relate two sets of vectors.
Acta Crystallogr. A 32 , 922–923.
Larkin, C., Datta, S., Nezami, A., Dohm, J.A., and Schildbach, J.F. (2003).
Crystallization and preliminary X-ray characterization of the relaxase domain
of F factor TraI. Acta Crystallogr. D Biol. Crystallogr. 59 , 1514–1516.
Laskowski, R.A., and Swindells, M.B. (2011). LigPlot+: multiple ligand-protein
interaction diagrams for drug discovery. J. Chem. Inf. Model 51 , 2778–2786.
Lawley, T.D., Klimke, W.A., Gubbins, M.J., and Frost, L.S. (2003). F factor
conjugation is a true type IV secretion system. FEMS Microbiol. Lett. 224 ,
1–15.
Lederberg, J., and Tatum, E.L. (1946). Gene recombination inEscherichia coli.
Nature 158 , 558.
Low, H.H., Gubellini, F., Rivera-Calzada, A., Braun, N., Connery, S., Dujean-
court, A., Lu, F., Redzej, A., Fronzes, R., Orlova, E.V., and Waksman, G.
(2014). Structure of a type IV secretion system. Nature 508 , 550–553.
Manchak, J., Anthony, K.G., and Frost, L.S. (2002). Mutational analysis of
F-pilin reveals domains for pilus assembly, phage infection and DNA transfer.
Mol. Microbiol. 43 , 195–205.
Marvin, D.A., and Folkhard, W. (1986). Structure of F-pili: reassessment of the
symmetry. J. Mol. Biol. 191 , 299–300.
Mindell, J.A., and Grigorieff, N. (2003). Accurate determination of local defocus
and specimen tilt in electron microscopy. J. Struct. Biol. 142 , 334–347.
Novotny, C.P., and Fives-Taylor, P. (1974). Retraction of F pili. J. Bacteriol.
117 , 1306–1311.
Paiva, W.D., Grossman, T., and Silverman, P.M. (1992). Characterization of
F-pilin as an inner membrane component ofEscherichia coliK12. J. Biol.
Chem. 267 , 26191–26197.
Pettersen, E.F., Goddard, T.D., Huang, C.C., Couch, G.S., Greenblatt, D.M.,
Meng, E.C., and Ferrin, T.E. (2004). UCSF Chimera–a visualization system
for exploratory research and analysis. J. Comput. Chem. 25 , 1605–1612.
Richmond, G.S., Gibellini, F., Young, S.A., Major, L., Denton, H., Lilley, A., and
Smith, T.K. (2010). Lipidomic analysis of bloodstream and procyclic form Try-
panosoma brucei. Parasitology 137 , 1357–1392.
Riechmann, L., and Holliger, P. (1997). The C-terminal domain of TolA is the
coreceptor for filamentous phage infection ofE. coli. Cell 90 , 351–360.
Rivera-Calzada, A., Fronzes, R., Savva, C.G., Chandran, V., Lian, P.W., Laere-
mans, T., Pardon, E., Steyaert, J., Remaut, H., Waksman, G., and Orlova, E.V.
(2013). Structure of a bacterial type IV secretion core complex at subnano-
metre resolution. EMBO J. 32 , 1195–1204.
Silverman, P.M. (1997). Towards a structural biology of bacterial conjugation.
Mol. Microbiol. 23 , 423–429.
Tang, G., Peng, L., Baldwin, P.R., Mann, D.S., Jiang, W., Rees, I., and Ludtke,
S.J. (2007). EMAN2: an extensible image processing suite for electron micro-
scopy. J. Struct. Biol. 157 , 38–46.
Taylor, A.L., and Thoman, M.S. (1964). The Genetic Map ofEscherichia Coli
K-12. Genetics 50 , 659–677.
Thomas, C.M., and Nielsen, K.M. (2005). Mechanisms of, and barriers to,
horizontal gene transfer between bacteria. Nat. Rev. Microbiol. 3 , 711–721.
Wang, Y.A., Yu, X., Silverman, P.M., Harris, R.L., and Egelman, E.H. (2009).
The structure of F-pili. J. Mol. Biol. 385 , 22–29.
Winn, M.D., Ballard, C.C., Cowtan, K.D., Dodson, E.J., Emsley, P., Evans,
P.R., Keegan, R.M., Krissinel, E.B., Leslie, A.G., McCoy, A., et al. (2011).
Overview of the CCP4 suite and current developments. Acta Crystallogr. D
Biol. Crystallogr. 67 , 235–242.
Wollman, E.L., Jacob, F., and Hayes, W. (1956). Conjugation and genetic
recombination inEscherichia coliK-12. Cold Spring Harb. Symp. Quant.
Biol. 21 , 141–162.1444 Cell 166 , 1436–1444, September 8, 2016