FIG. 8.

(a) A surface volume representation of the Glu278Gln mutant at 9.8-Å resolution (green), wild-type capsid at 25 Å resolution (yellow), and wild-type procapsid at 28-Å resolution (blue) (6). A pseudoatomic model of the mutant particle was generated by fitting the atomic coordinates, as a rigid body, to the observed density values. 2, twofold axis. (b) Comparison of the Glu278Gln mutant capsid, wild-type capsid, and wild-type procapsid (6) radially averaged electron density distributions. The averaged outer edge of the mutant corresponded to an intermediate size (∼235 Å) compared to those of the procapsid (∼255 Å) and capsid (∼215 Å). (c) A view of the quasithreefold axis near Glu278. At the left is a closeup view of the Gln278 pseudoatomic model described for panel a at pH 5.0. Glu278 is shown in the crystal structure of the capsid at the right. In the capsid form, Glu278 is inserted into a cavity formed in the neighboring subunit. The cavity consists of residues Ala276, Phe282, Val283, and Pro489 (side chains are shown as stick models). These hydrophobic residues are surrounded by negative charges at pH 7.6; however, the charge is reduced at pH 5.0 (Fig. 5). The LCC in the Glu278Gln particle was inhibited by this substitution, indicating that the self-repulsion between symmetry-related Glu278 residues plays a crucial role in the cavity insertion.