Figure 3

Topology diagrams for CstII (PDB ID: 1RO7) and modeled ST3Gals. Triangles and circles represent strands and helices, respectively. Strands 5' and 8 are antiparallel to other strands in ST3Gals and are hence inverted. Certain helices and strands are not found in all the modeled ST3Gals (Figure 1) and these are represented by dotted lines. The nomenclature used to identify strands and helices in CstII are the same as those used by Chiu et al. [13]. The equivalent secondary structure elements in ST3Gals are identified by the same names. Strand 9 and helices D, G and H are absent in ST3Gals; strand 5' and helix K' are absent in CstII. Note that the region of the polypeptide from strand 8 till helix K is at the C-terminus in CstII but they are at the N-terminus in ST3Gals; hence, the direction of the polypeptide chain is opposite to one another in this region.