The molecular structure of some insect virus inclusion bodies

Abstract

Electron microscopic investigation have revealed very regular dot and line patterns in different crystalline insect virus inclusion bodies, the so-called polyhedra and capsules. The crystalline lattice has a very high degree of regularity without dislocations. Contrary to previous results, it was found that the inclusion body protein molecules are not ellipsoids arranged in a pseudohexagonal system, but spheres arranged in a face-centered cubic system. Between the molecule rows, angles of 90 and 125 degrees could readily be observed. The diameters of the molecules vary from about 65 to 90 A, depending on the insect specied from which the inclusion bodies were obtained. All observed dot and line patterns could be explained with the aid of light and X-ray micrographs of molecule models arranged in a cubic system, but cut at different angles. X-ray photographs of the molecule models suggest that sections were in the neighborhood of about 100 A thick since only sections of such a thickness reveal electron-density differences great enough to resolve dot patterns of more than 90 degree angles between the rows. The arrangement of inclusion body protein molecules in a face-centered cubic system indicated that there are six relative points of special attraction on the surface of each molecule, which leads to the cubic system. Without these selective points of attraction, one would expect a close-packed hexagonal arrangement which never could be found in any of the inclusion bodies. Virus particles, irregularly distributed and in random position within the inclusion bodies, do not disturb the crystalline lattice, or act as crystallization centers. No other components were ever found within the crystalline lattice of the inclusion bodies.