Structural modeling of the geminiviral capsid proteins (CPs). (A) Pseudo-atomic models of the CPs of Panicum streak virus (Mastre; red), Mesta yellow vein mosaic virus (Begomo; green), Horseradish curly top virus (Curto; orange) and Tomato pseudo-curly top virus (Topocu; cyan) are compared to the atomic model of the CP of Satellite tobacco necrosis virus (STNV; blue; [PDB:2buk]). (B) Comparison of the stereochemical quality of the STNV CP X-ray structure to that of the pseudo-atomic models of geminiviral CPs. (C) Structure-based alignment of geminiviral CP sequences to the corresponding protein sequence of STNV. Residues that are identical or similar in the STNV CP and in at least one geminiviral sequence are boxed in black or gray, respectively. The secondary structure determined from the X-ray structure of STNV CP [PDB:2buk] is shown above the alignment with α helices, β strands, and turns represented by red rectangles, blue arrows, and yellow bulges, respectively. The nomenclature for the secondary structure elements (βB-βI) is also indicated .