Publication details
The Structure of Bacteriophage phi Cb5 Reveals a Role of the RNA Genome and Metal Ions in Particle Stability and Assembly
| Authors | |
|---|---|
| Year of publication | 2009 |
| Type | Article in Periodical |
| Magazine / Source | Journal of Molecular Biology |
| MU Faculty or unit | |
| Citation | |
| Doi | http://dx.doi.org/10.1016/j.jmb.2009.06.047 |
| Field | Biochemistry |
| Keywords | virus; structure; assembly; calcium; RNA |
| Description | The structure of the Leviviridae bacteriophage phi Cb5 virus-like particle has been determined at 2.9 angstrom resolution and the structure of the native bacteriophage phi Cb5 at 3.6 angstrom. The structures of the coat protein shell appear to be identical, while differences are found in the organization of the density corresponding to the RNA. The capsid is built of coat protein dimers and in shape corresponds to a truncated icosahedron with T=3 quasi-symmetry. The capsid is stabilized by four calcium ions per icosahedral asymmetric unit. One is located at the symmetry axis relating the quasi-3-fold related subunits and is part of an elaborate network of hydrogen bonds stabilizing the interface. The remaining calcium ions stabilize the contacts within the coat protein dimer. The stability of the phi Cb5 particles decreases when calcium ions are chelated with EDTA. In contrast to other leviviruses, phi Cb5 particles are destabilized in solution with elevated salt concentration. The model of the phi Cb5 capsid provides an explanation of the salt-induced destabilization of phi Cb5, since hydrogen bonds, salt bridges and calcium ions have important roles in the intersubunit interactions. Electron density of three putative RNA nucleotides per icosahedral asymmetric unit has been observed in the phi Cb5 structure. The nucleotides mediate contacts between the two subunits forming a dimer and a third subunit in another dimer. We suggest a model for phi Cb5 capsid assembly in which addition of coat protein dimers to the forming capsid is facilitated by interaction with the RNA genome. The phi Cb5 structure is the first example in the levivirus family that provides insight into the mechanism by which the genome-coat protein interaction may accelerate the capsid assembly and increase capsid stability. (C) 2009 Elsevier Ltd. All rights reserved. |