Figure 4. The N- and C-termini from CagT-1 and CagT-2 are positioned differently.

(a–c) The N-terminus of CagT-1 extends inward toward the center of the map and interacts with CagX from the next asymmetric unit. The residues that contribute to this interaction are largely hydrophobic, as indicated in the inset panel. CagT-2 differs from CagT-1 in that the N-terminus of the protein extends outward toward the periphery of the map, forming the last strand of a β-sheet with Cag3-1. (d) The three proteins (CagT-1, CagT-2 and Cag3-1) have an interwoven architecture. (e) The interface that is formed between the three proteins consists of two β-sheets that include strands from all three molecules. (f) The interface of CagT-2 and Cag3-1 is a pair of α-helices that bury hydrophobic residues within the interface. (g) The position of the N-terminal loops of CagT-1 (red) and CagT-2 (salmon) are such that the putative lipidation sites are near the outer membrane. (h) The C-terminal α-helices of CagT-1 adopt an extended conformation (left) and interact with Cag3-1, Cag3-2, and Cag3-4 within the same asymmetric unit and Cag3-1 and CagT-1 in neighboring asymmetric units (right). (i) The C-terminal α-helices of CagT-2 are connected by an apparently flexible linker (left) and interact with Cag3-1, Cag3-2, and CagM-1 (right).

Figure 4—figure supplement 1. The N-terminal loop of CagT is observed in two different conformations.

(a) The dihedral angles of residues within the N-terminal loop of CagT-1 and CagT-2 are plotted. The difference between the angles was used to determine where the largest change occurred. Residues in which both the φ and ψ angles changed by >1° are highlighted in yellow. (b) The N-terminal loop of CagT-1 (red) and CagT-2 (salmon) is highlighted in yellow. (c) The residues of CagT-1 and CagT-2 that exhibited the most striking change are depicted. (d) Residues within these loops engage in protein-protein interactions with different subsets of proteins. The table lists relevant residues along with the type of interaction mediated and the interacting protein. Arrows indicate residues with different interacting partners. (e) The orientations of the N-terminal loops are shown. A loop of CagT-1 interacts with CagX and a loop of CagT-2 completes a β-sheet formed by Cag3. (f) The interactions mediated by the N-terminal loops are shown here. The top row depicts interactions mediated by the N-terminal loop of CagT-1, and the bottom row depicts interactions mediated by the N-terminal loop of CagT-2. Proteins are colored as they appear in panel (e), with proteins from adjacent asymmetric units depicted with gray density.

Figure 4—figure supplement 2. The C-terminal helices of CagT mediate interactions within the OMC.

(a) Domain diagrams of H. pylori CagT and X. citri VirB7. The two proteins have similar N-terminal domains that mediate interactions with other components in the respective T4SSs. CagT contains three additional helices within the C-terminus of the protein that mediate interactions with adjacent asymmetric units. (b) The three C-terminal helices of CagT-1 and CagT-2 observed within the WT map are shown with experimental density displayed as a mesh (top). Landmark residues demonstrating the accuracy of the register are shown. The two C-terminal helices of CagT-1 that were observed within the ΔCag3 map are shown with experimental density displayed as a mesh (bottom). Landmark residues demonstrating the accuracy of the register are shown.