HK97 and related protein structures with common features high-lighted. (A) HK97 in the immature state (PDB: 3E8K), (B) P22, (C) T4, (PDB: 1YUE), (D) BPP-1 (PDB: 3J4U), and (E) P-SSP7 (PDB: 2XD8). The common features are N-arm (red), E-loop (yellow), P-domain (green), A-domain (cyan), β-hinge (orange). (F) An electron density map of the HK97 capsid with capsomers (both the hexamer [6-asymmetric subunits, multicolored] and the pentamer [red]) indicated. Parts A–E adapted from ref. 124 with permission from Elsevier, copyright 2015. Part F adapted from ref. 125 with permission from Nature Publishing Group, copyright 2009.