The Geminiviridae is an extensive family of plant viruses responsible for economically devastating diseases in crops worldwide. Geminiviruses package circular, single-stranded DNA (ssDNA) genomes. The characteristic twinned or "geminate" particles, which consist of two joined, incomplete T = 1 icosahedra, are unique among viruses. We have determined the first structure of a geminivirus particle, the Nigerian strain of Maize streak virus (MSV-N), using cryo-electron microscopy and three-dimensional image reconstruction methods. The particle, of dimensions 220 x 380 Å, has an overall 52-point-group symmetry, in which each half particle "head" consists of the coat protein (CP) arranged with quasi-icosahedral symmetry. We have modeled the MSV-N CP as an eight-stranded, antiparallel β-barrel motif (a structural motif common to all known ssDNA viruses) with an N-terminal α-helix. This has produced a model of the geminate particle in which 110 copies of the CP nicely fit into the reconstructed density map. The reconstructed density map and MSV-N pseudo-atomic model demonstrate that the geminate particle has a stable, defined structure.
Bibliographical noteFunding Information:
We thank I. Portman for technical assistance in the purification of MSV-N, P. Chipman for microscopy of initial MSV samples and for recording the image used in Fig. 1A, and Y. Tao and R. Ashmore for assistance with programming. This work was supported in part by NIH Grant GM33050 and NSF Shared Instrumentation Grant BIR-9112921 to T.S.B., a BBSRC Grant 88/B11521 to R.M., a Purdue Research Foundation Fellowship to W.Z., and a BBSRC postgraduate studentship 98/A1/ B/04565 to L.F. The John Innes Centre is grant-aided by the BBSRC.
- Cryo-electron microscopy
- Icosahedral capsid
- Maize streak virus
- Three-dimensional image reconstruction
- ssDNA virus