Model building of the 3D structure of the soybean expansin protein (GmEXPA1) based on its similarity to the Zea m 1 (Protein Data Bank [PDB] code: 2HCZ). Seven critical amino acid sites responsible for both functional divergence and positive selection are shown to varying degrees in (A), (B), and (C). The figure was produced using the Swiss-model and pyMOL programs. (A) The overall view of the seven critical amino acid sites on the 3D structure. The seven sites are labeled in red. (B) View of critical amino acid sites on the surface of GmEXPA1. Four amino acid sites responsible for both functional divergence and positive selection located on the surface of the molecule are colored red. Of these amino acid sites, 190S and 192 T may be critical for polysaccharide binding of domain II. The gray area represents the N and C termini. (C) Critical amino acid sites related to the contact of the two domains. Only the two domains are shown to better exhibit the two residues, 172 L and 196P, which may be related to the contact of the two domains.