The refined crystal structure of cowpea mosaic virus at 2.8 Å resolution

Comoviruses are a group of plant viruses in the picornavirus superfamily. The type member of comoviruses, cowpea mosaic virus (CPMV), was crystallized in the cubic space group 123, a = 317 Angstrom and the hexagonal space group P6(1)22, a = 451 Angstrom, c = 1038 Angstrom. Structures of three closely similar nucleoprotein particles were determined in the cubic form. The roughly 300-Angstrom capsid was similar to the picornavirus capsid displaying a pseudo T = 3 (P = 3) surface lattice. The three beta-sandwich domains adopt two orientations, one with the long axis radial and the other two with the long axes tangential in reference to the capsid sphere. T = 3 viruses display one or the other of these two orientations. The CPMV capsid was permeable to cesium ions, leading to a disturbance of the beta-annulus inside a channel-like structure, suggesting an ion channel. The hexagonal crystal form diffracted X rays to 3 Angstrom resolution, despite the large unit cell. The large (similar to 200 Angstrom) solvent channels in the lattice allow exchange of CPMV cognate Fab fragments. As an initial step in the structure determination of the CPMV/Fab complex, the P6(1)22 crystal structure was solved by molecular replacement with the CPMV model determined in the cubic cell. (C) 1999 Academic Press.