(A) Cryo-EM densities of the CATC surrounding a penton vertex. The
density map was low-pass filtered to 6-Å resolution to show the flexible
pUL25 head region. (B) Magnified view of a segmented-out CATC unit
from the dashed square in (A), showing its composition. (C) Fitting
of two copies of pUL25 C-terminal region crystal structure (PDB 2F5U) (22) into the bi-lobed head region of CATC.
The contour level for the pUL25 head region in (A) to (C) was 1.5d (where d is
the standard deviation) and that of the rest was 3d. (D and
E) Top view (D) and side view (E) of CATC interacting with
underlying capsid components, shown with atomic models. On the left in (E) is a
magnified view of the interface between the CATC and triplex Tc. Hydrophobic
side chains of the pUL25 dimer, Tri1, and Tri2B involved in the interactions are
highlighted. (F and G) Domain organization of pUL17
(F) and pUL25 (G). (H and I) The five-helix bundle
viewed from the top of the capsid (H) or along the center of the coiled coil
(I). In (H), side chains are shown for hydrophobic residues in the center of the
helix bundle (top), with their identities marked (grayed) in the sequence
(bottom). The arrowhead in (H) points to the position in the pUL25 sequence
where the hydrophobic residue distribution pattern breaks. Nʹ, N
terminus; Cʹ, C terminus.