FIG 1.

CHIKV/SFV E2 chimeras have several differences in interacting residues. (A) Top view of the published structure 2XFC in a cartoon tube. CHIKV E1 subunits are shown in blue, red, and orange. CHIKV E2 subunits are shown in green, yellow, and purple. E3 (from PDB 3N42) is shown as the lime green surface. Subunit backbone colorations are the same in subsequent panels. (B) Expanded view of the CHIKV E2 subunit. Domain A is yellow, domain B is orange, and domain C is blue. SFV residues which are substituted in the three different chimeras are shown in cyan, magenta, and yellow sticks for domains A, B, and C, respectively. (C to E) Wild-type (WT) CHIKV residues are shown as sticks. Residues in E1 are shown as sticks colored to match the backbone. Green sticks represent WT E2 residues which differ in the chimeras, and orange sticks represent WT residues that do not change in the chimeras. (C) Two intermolecular hydrogen bonds and one intramolecular salt bridge are lost, and one intermolecular salt bridge is weakened when SFV residues replace CHIKV residues in domain A. (D) One hydrogen bond is lost with a backbone carbonyl of E1 when K200 in CHIKV is substituted with N200 of SFV domain B. E3 does not make contact with substituted residues. (E) CHIKV E2 interacts with two E1 subunits at domain C. Three substitutions disrupt a hydrophobic pocket for I387 of one E1 subunit, and two hydrogen bonds and one stacking/hydrophobic interaction are lost in the other E1 when SFV substitutions are made. For panels C to E, see Table 2 for specific residues and interactions. (F) The amino acid sequences of CHIKV, VEEV, and SFV E2 were aligned using ClustalW and are displayed using ESPript. Colored bars above the alignment represent each of the domains, which correspond to the color shown in panels A to E.