Figure 2.
Encapsulin structure and assembly. (A) Structure of the Family 1 encapsulin protomer from Thermotoga maritima (PDB ID: 3DKT).3 Core HK97 phage-like domains (A-domain, P-domain, E-loop) are highlighted. The bar below the structure represents the locations of the annotated domains according to amino acid sequence. (B) Family 2 encapsulin protomers from Synechococcus elongatus (2A, PDB ID: 6X8T) and Streptomyces griseus (2B, PDB ID: 9BHV).7,9 Dashed lines represent disordered or unresolved structural features. Variable lengths of the Family 2 N-extensions are shown in the inserted plot (adapted with permission from ref 2).2 (C) Left: Family 1 encapsulin shells of T. maritima, Myxococcus xanthus (T = 3, PDB ID: 7S20), and Quasibacillus thermotolerans (T = 4, PDB ID:6NJ8).3,11,45 Right: Family 2 encapsulin shells from S. elongatus, S. griseus, and a model of a two-component shell from Streptomyces lydicus (2B, PDB IDs: 9BJE, 9BIX).7,9,18 Pentameric facets are shown in blue, CBDs are shown in green, and Enc 1 of the two-component shell is shown in light blue and light green for the encapsulin backbone and the CBD, respectively. (D) Interior and exterior views of the closed 2-fold pore of the S. elongatus Family 2A encapsulin shell.7 The N-arm and N-helix are shown in yellow to highlight their position at the 2-fold pore. E-loops were removed to better highlight the pore region. (E) The open 2-fold pore of the Sg Enc Family 2B encapsulin shell from S. griseus.9 E-loops and CBDs are not shown for visual clarity. (F) The open and closed pore states observed in the S. lydicus two-component shell.18