Figure 4
Overall structural similarity between TSP4-N335 (right) and phage T4 gp10 (PDB 5IV5) (left) with each subunit shown in different color. The gp10 C-terminal region would have a counterpart in TSP4 D1-D4 region if TSP4 adopted a similar overall shape. All TSP4-N335 domains adhere to the same threefold symmetry axis. In contrast, each XD module of gp10 utilizes a different threefold symmetry axis to form differently oriented closely packed trimers. The tail baseplate gp10 partner proteins gp11 (green) and gp12 (orange) bind across the threefold axes of the trimeric XD3 and XD2 domains of gp10, respectively. The XD2 modules of TSP4-N335 do not pack together and lack such binding surface. However, the TSP4-N250 structure, devoid of the XD3 domain, exhibits closely associated XD2 trimers with a surface that can bind a trimeric partner (Fig. 2C).
