Structural properties of the EIAV gp45 protein. (A) Schematic representation of EIAV gp45. FP: fusion peptide; FPPR: fusion peptide proximal region; NHR: N-terminal Heptad Repeats; CHR: C-terminal Heptad Repeats; MPER: membrane proximal external region; TM: transmembrane domain; CTT: C-terminal tail. The residue numbers for demarcation of each region are shown. (B) Crystal structure of the wild-type (WT) protein, gp45WT. The full-length trimer formed through crystallographic symmetry is shown as a ribbon model. The core of the gp45WT has been highlighted to represent the NHR (green) and CHR (forest green) domains, and the TEV sequence is shown in palegreen. (C) Top view of the surface charge potential of gp45 pocket. Here the negatively charged residues are colored in red and positively charged residues in blue. (D) Superimposed structures of the EIAV gp45WT and the HIV gp41, including the FPPR (fusion peptide proximal, salmon) and MPER (membrane proximal external, warm pink) regions (PDB code 2X7R). The EIAV gp45WT are displayed as in (B), but the TEV sequence is removed for clarity. The HIV gp41 NHR and CHR domains are highlighted in red and raspberry colors, respectively. (E) The water clusters (represented as red spheres) within EIAV gp45WT trimer.