An icosahedral algal virus has a complex unique vertex decorated by a spike

Abstract

Paramecium bursaria Chlorella virus-1 is an icosahedrally shaped, 1,900-Å-diameter virus that infects unicellular eukaryotic green algae. A 5-fold symmetric, 3D reconstruction using cryoelectron microscopy images has now shown that the quasiicosahedral virus has a unique vertex, with a pocket on the inside and a spike structure on the outside of the capsid. The pocket might contain enzymes for use in the initial stages of infection. The unique vertex consists of virally coded proteins, some of which have been identified. Comparison of shape, size, and location of the spike with similar features in bacteriophages T4 and P22 suggests that the spike might be a cell-puncturing device. Similar asymmetric features may have been missed in previous analyses of many other viruses that had been assumed to be perfectly icosahedral.5-fold averaging ͉ cryoelectron microscopy reconstruction ͉ Paramecium bursaria Chlorella virus-1 ͉ cell entry ͉ specialized vertex protein

Three-dimensional structure and function of the Paramecium bursaria chlorella virus capsid

“…The spike assembly is held in place by the five peripentonal capsomers (18). The component of the spike assembly inside the viral capsid was previously described (18) as being about the same size and shape as the portal protein of tailed bacteriophages such as phi29 (34), SPP1 (35), and P22 (36,37). However, the wide basal end of the PBCV-1 spike assembly encloses a roughly spherically closed cavity (Fig.…”

“…From the base on the viral surface, the spike structure widens to about 160 Å inside the capsid and forms a closed cavity inside the large pocket between the capsid and the membrane under the unique vertex. The spike assembly is held in place by the five peripentonal capsomers (18). The component of the spike assembly inside the viral capsid was previously described (18) as being about the same size and shape as the portal protein of tailed bacteriophages such as phi29 (34), SPP1 (35), and P22 (36,37).…”

“…The structure fits well into the cryoEM density map of PBCV-1. Using fivefold (as opposed to icosahedral) symmetry in calculating the cryoEM image reconstruction Cherrier et al (18) showed that there exists a unique fivefold vertex with a spike structure extending outward. Underneath the spike there is a pocket between the capsid and the internal membrane presumably enveloping the nucleocapsid composed of the genome and other proteins.…”

Chlorovirus ATCV-1 is part of the human oropharyngeal virome and is associated with changes in cognitive functions in humans and mice

“…These researchers were primarily evaluating bacteriophages (7,8,31). The icosahedral-shaped chloroviruses are 190 nm in diameter and have a 34-nm spike structure protruding from one unique vertex (32). Therefore, it is likely that ATCV-1 and most chloroviruses would be trapped on a 0.2-μm filter.…”

Potassium Ion Channels: Could They Have Evolved from Viruses?

“…PBCV-1 attaches to the cell wall of its host via a spike structure that is present at one of the icosahedral vertices of the virus particles (Cherrier et al, 2009;Zhang et al, 2011). Attachment is followed by localized degradation of the host wall by a viruspackaged enzyme or enzymes (Meints et al, 1984).…”