Figure 1 - full size

Figure 1. Figure 1. Structure of SFV E1 (A) Ribbon diagram colored according to domains, by using the standard class II color coding (red, yellow, and blue for DI, DII, and DIII, respectively), except that DII is colored yellow and orange to distinguish the two insertions into DI loops (at D[0]E[0] and H[0]I[0]) that make up this domain, and the fusion peptide is brown. The SS bonds are drawn as green cylinders and are labeled from 1 to 8. A yellow fan denotes the single glycosylation site at position 141. All of the histidine side chains present in the structure are drawn in magenta and labeled; conserved ones are framed (note the cluster of three histidines at the DI/DIII interface, around His331). The side chains of mutants that affect the lipid dependence of the fusion activity of E1 are drawn and labeled in black. Numbered gray arrows point to the location of E1 insertions in the more distant fish alphaviruses (see [C]). (B) Topological diagram of E1, drawn with TOPS (Flores et al., 1994) and colored according to domains. The domains are labeled in colored font (matching the class II scheme). In DII, the central and connecting b sheets and the fusion loop-bearing b sandwich (FLBS) are labeled in black. (C) Amino acid sequence alignment of E1 proteins from representative alphaviruses: Ross river virus (RRV), O'nyong-nyong virus (NYO), Venezuelan equine encephalitis virus (VEE), western equine encephalitis virus (WEE), Sindbis virus (SIN), and rainbow trout sleeping disease virus (SDV). The secondary structure is represented above the sequence, colored coded as in (A) and (B). Highly and relatively conserved residues are drawn in white font on red background and vice versa, respectively, with variable positions in black. The glycosylation site is marked by a yellow fan as in (A). Cysteines are labeled in green with the number of the disulfide bridge that they form (1-8, as in [A]). Insertions in the amino acid sequence of E1 from the fish alphaviruses (SDV) are numbered in gray to match the arrows in (A). Other symbols underneath the alignment show E1/E1 (triangles) and E1/E2 (blue stars) contacts on the virus particle, determined as indicated in the Experimental Procedures. Yellow triangles denote E1/E1 contacts about the I5 and Q6 axes (Figure 2), and white triangles denote contacts about the Q2 axes. A vertical open arrow above the sequence marks the last amino acid with visible electron density in the crystal (K384). The C-terminal TM region is boxed.