The catalytic domain and SKS domain.

<p>SKS domain shown in green cartoon and the catalytic domain shown in aquamarine cartoon. The catalytic triad is represented as yellow sticks. (<b>A</b>) Conservation of the catalytic triad evidenced by the structural superposition. The catalytic fold of DPP4 is shown as red cartoon. DPP7 catalytic residues (Ser-162, Asp-418 and His-443) are colored in yellow, while DPP4 catalytic residues (Asp-708, His-740 and Ser-630) in green. The corresponding amino acid numbers are shown in black. (<b>B</b>) The SKS domain is shown in green cartoon, while the glycans linked to Asn363 and Asn315 are shown as sticks. Both glycans seem to have a scaffold function by holding the loop Glu354-Asp375 to the helix α8 and the loop Asp324-Tyr314 to the helix α12, respectively. (<b>C</b>) Four disulfide bonds present in the SKS domain. Cys216-Cys293 and Cys246-Cys322 seem to have a structure stabilization role. Cys332-Cys338 is very likely involved in the activity regulation of the enzyme, while Cys352-Cys382 could play either regulatory and structural role. The figure was prepared using the program PyMOL (<a href="http://www.pymol.org/" target="_blank">http://www.pymol.org/</a>).