Electron tomography and simulation of baculovirus actin comet tails support a tethered filament model of pathogen propulsion.
Several pathogens induce propulsive actin comet tails in cells they invade to disseminate their infection. They achieve this by recruiting factors for actin nucleation, the Arp2/3 complex, and polymerization regulators from the host cytoplasm. Owing to limited information on the structural organization of actin comets and in particular the spatial arrangement of filaments engaged in propulsion, the underlying mechanism of pathogen movement is currently speculative and controversial. Using electron tomography we have resolved the three-dimensional architecture of actin comet tails propelling baculovirus, the smallest pathogen yet known to hijack the actin motile machinery. Comet tail geometry was also mimicked in mixtures of virus capsids with purified actin and a minimal inventory of actin regulators. We demonstrate that propulsion is based on the assembly of a fishbone-like array of actin filaments organized in subsets linked by branch junctions, with an average of four filaments pushing the virus at any one time. Using an energy-minimizing function we have simulated the structure of actin comet tails as well as the tracks adopted by baculovirus in infected cells in vivo. The results from the simulations rule out gel squeezing models of propulsion and support those in which actin filaments are continuously tethered during branch nucleation and polymerization. Since Listeria monocytogenes, Shigella flexneri, and Vaccinia virus among other pathogens use the same common toolbox of components as baculovirus to move, we suggest they share the same principles of actin organization and mode of propulsion.
Institute of Molecular Biotechnology, Austrian Academy of Sciences, Vienna, Austria.
Jan
J
Mueller
Institute of Molecular Biotechnology, Austrian Academy of Sciences, Vienna, Austria.
Julia
J
Pfanzelter
RICAM, Austrian Academy of Sciences, Vienna, Austria ; Faculty of Mathematics, University of Vienna, Austria.
Christoph
C
Winkler
Nagoya University, Graduate School of Sciences, Structural Biology Research Center and Division of Biological Sciences, Nagoya, Japan ; Nagoya University JST PRESTO, 4-1-8 Honcho Kawaguchi, Saitama, Japan.
Akihiro
A
Narita
Laboratoire d'Enzymologie et Biochimie Structurales, Centre National de la Recherche Scientifique, Gif-sur-Yvette, France.
Christophe
C
Le Clainche
Institute of Molecular Biotechnology, Austrian Academy of Sciences, Vienna, Austria.
Maria
M
Nemethova
Laboratoire d'Enzymologie et Biochimie Structurales, Centre National de la Recherche Scientifique, Gif-sur-Yvette, France.
Marie-France
MF
Carlier
Nagoya University, Graduate School of Sciences, Structural Biology Research Center and Division of Biological Sciences, Nagoya, Japan.
Yuichiro
Y
Maeda
Department of Molecular and Cell Biology, University of California, Berkeley, California, United States of America.
Matthew D
MD
Welch
Department of Molecular and Cell Biology, University of California, Berkeley, California, United States of America.
Taro
T
Ohkawa
RICAM, Austrian Academy of Sciences, Vienna, Austria ; Faculty of Mathematics, University of Vienna, Austria.
Christian
C
Schmeiser
Campus Science Support Facilities GmbH, Vienna, Austria.
Guenter P
GP
Resch
Institute of Molecular Biotechnology, Austrian Academy of Sciences, Vienna, Austria.
J Victor
JV
Small
D008841:Actin Cytoskeleton / Q000378:metabolism / Q000648:ultrastructure*; D051376:Actin-Related Protein 2-3 Complex / Q000378:metabolism / Q000648:ultrastructure*; D000818:Animals; D016367:Baculoviridae / Q000737:chemistry / Q000502:physiology / Q000648:ultrastructure*; D020552:Comet Assay; D055032:Electron Microscope Tomography; D015870:Gene Expression; D017930:Genes, Reporter; D006054:Goldfish; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008546:Melanoma, Experimental; D015233:Models, Statistical; D061987:Sf9 Cells; D018411:Spodoptera; D000097573:Red Fluorescent Protein
D051376:Actin-Related Protein 2-3 Complex; D049452:Green Fluorescent Proteins; D008164:Luminescent Proteins; D000097573:Red Fluorescent Protein