Figure 3. C-terminus of DHBc CPs and the N-terminus of HBc occupy the same site.

(a) The AB-dimers of HBc (pdb: 6HTX Böttcher and Nassal, 2018) and b of DHBc in the same orientation. For clarity the extension domain (78-120) is not shown. Large-type and small-type CPs show a structurally conserved hand region and lower spike arrangement with an RMSD of 1.9 Å (Figure 3—figure supplement 1). Major differences are the packing of the four helices in the upper part of the spike and the site at the base of the spikes. This is occupied either by the 12 N-terminal residues of chain A of HBc or by the 12 C-terminal residues of DHBc (magenta). The protruding tip of the extension domain in one CP of DHBc provides a similar structural environment as the tips of the spikes in a CP dimer of HBc (Figure 3—figure supplement 2).

Figure 3—figure supplement 1. The fold of the lower part of HBc and DHBc CPs have an RMSD of 1.9 Å.

Chain C of HBc and DHBc were superposed with the match align tool of Chimera. The 113 matching amino acids (light blue for DHBc and light red for HBc) had an overall RMSD of 1.9 Å. The none-matching parts (red for HBc and blue for DHBc, RMSD >5 Å) cluster to the upper half of the spike and at the N-terminus. (a and b) show two different views which are related by 90° rotation around the vertical axis.

Figure 3—figure supplement 2. The extension domain of DHBc provides a similar structural environment as the tips of the spikes in HBc.

The tips of the AB-dimer of HBc (6HTX, residues 73–83 of chains A and B, blue and cyan) were fitted as rigid body to the two extension domains in a DHBc-dimer. The map is the same as shown for the asymmetric unit in Figure 1—figure supplement 4 but without B-factor sharpening. (a) Shows a view parallel to the dimer axis and (b) perpendicular to the dimer axis.