Figure 2.
Interactions involved in the intertrimer interface of dodecahedral E2p compared with that of the cubic E2p interface. The two protomers involved in the interface are drawn in red and blue, respectively. Residues belonging to the red subunit are labeled in red and colored in black (oxygen), gray (nitrogen), green (sulfur), and white (carbon), whereas residues from the blue subunit are labeled in black and colored in red (oxygen), blue (nitrogen), green (sulfur), and yellow (carbon). Hydrogen bonds are indicated by a dotted line. (A) In the B. stearothermophilus interface, the Met-425 anchor residue of the red subunit interacts with the hydrophobic pocket of the blue subunit lined by residues His-237, Phe-241, Ile-244, Leu-252, Ile-314, and Phe-315. Also, a salt bridge is formed between His-237 (blue subunit) and Glu-421 (red subunit). Hydrogen bonds involving the backbone are formed between residues Ile-314 (blue subunit) and Leu-424 (red), Phe-315 (blue) and Met-425 (red), and Arg-267 (blue) and Arg-311 (red). (B) The E. faecalis E2p trimer–trimer interface is very similar to the one observed in B. stearothermophilus E2p (shown in A). The hydrophobic anchor here is Met-537 (red). The hydrophobic pocket is lined (in blue) by residues His-348, Phe-352, Val-355, Leu-363, Met-425, and Phe-426. (C) In the A. vinelandii E2p interface, the anchor residue Leu-637 (red subunit) interacts with the corresponding hydrophobic pocket lined by residues from the blue subunit Phe-449, Gln-453, Val-456, Leu-464, Leu-526, and Leu-527. The residues involved are equivalent to those in A and B (Table 2; Fig. 3). A salt bridge unique to this octahedral structure is formed by Arg-633 (red) and Glu-445 (blue).