Journal: mBio / Year: 2013 Title: Structure of a protozoan virus from the human genitourinary parasite Trichomonas vaginalis. Authors: Kristin N Parent / Yuko Takagi / Giovanni Cardone / Norman H Olson / Maria Ericsson / May Yang / Yujin Lee / John M Asara / Raina N Fichorova / Timothy S Baker / Max L Nibert / Abstract: The flagellated protozoan Trichomonas vaginalis is an obligate human genitourinary parasite and the most frequent cause of sexually transmitted disease worldwide. Most clinical isolates of T. ...The flagellated protozoan Trichomonas vaginalis is an obligate human genitourinary parasite and the most frequent cause of sexually transmitted disease worldwide. Most clinical isolates of T. vaginalis are persistently infected with one or more double-stranded RNA (dsRNA) viruses from the genus Trichomonasvirus, family Totiviridae, which appear to influence not only protozoan biology but also human disease. Here we describe the three-dimensional structure of Trichomonas vaginalis virus 1 (TVV1) virions, as determined by electron cryomicroscopy and icosahedral image reconstruction. The structure reveals a T = 1 capsid comprising 120 subunits, 60 in each of two nonequivalent positions, designated A and B, as previously observed for fungal Totiviridae family members. The putative protomer is identified as an asymmetric AB dimer consistent with either decamer or tetramer assembly intermediates. The capsid surface is notable for raised plateaus around the icosahedral 5-fold axes, with canyons connecting the 2- and 3-fold axes. Capsid-spanning channels at the 5-fold axes are unusually wide and may facilitate release of the viral genome, promoting dsRNA-dependent immunoinflammatory responses, as recently shown upon the exposure of human cervicovaginal epithelial cells to either TVV-infected T. vaginalis or purified TVV1 virions. Despite extensive sequence divergence, conservative features of the capsid reveal a helix-rich fold probably derived from an ancestor shared with fungal Totiviridae family members. Also notable are mass spectrometry results assessing the virion proteins as a complement to structure determination, which suggest that translation of the TVV1 RNA-dependent RNA polymerase in fusion with its capsid protein involves -2, and not +1, ribosomal frameshifting, an uncommonly found mechanism to date.
History
Deposition
Sep 5, 2012
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Header (metadata) release
Oct 10, 2012
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Map release
Apr 24, 2013
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Update
Apr 24, 2013
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Current status
Apr 24, 2013
Processing site: PDBe / Status: Released
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Structure visualization
Movie
Surface view with section colored by density value
Cryogen name: ETHANE / Chamber humidity: 99 % / Chamber temperature: 90 K / Instrument: HOMEMADE PLUNGER / Method: blot for 5 sec before plunging
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Electron microscopy
Microscope
FEI POLARA 300
Temperature
Min: 90 K / Max: 90 K
Alignment procedure
Legacy - Astigmatism: Objective lens astigmatism was corrected at high magnification
Date
Apr 26, 2012
Image recording
Category: FILM / Film or detector model: KODAK SO-163 FILM / Digitization - Scanner: OTHER / Digitization - Sampling interval: 1.09 µm / Number real images: 84 / Average electron dose: 22 e/Å2 / Bits/pixel: 8
Tilt angle min
0
Tilt angle max
0
Electron beam
Acceleration voltage: 200 kV / Electron source: FIELD EMISSION GUN
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