Ribbon diagram of human <a href="https://en.wikipedia.org/wiki/Dipeptidyl_peptidase-4" class="extiw" title="w:Dipeptidyl peptidase-4">dipeptidyl peptidase-4</a>.<br>Created using <a rel="nofollow" class="external text" href="http://www.accelrys.com/products/downloads/ds_visualizer/index.html">Accelrys DS Visualizer Pro 1.6</a> and <a href="https://en.wikipedia.org/wiki/GIMP" class="extiw" title="w:GIMP">the GIMP</a>.
Own work.
From <a href="https://en.wikipedia.org/wiki/Protein_Data_Bank" class="extiw" title="w:Protein Data Bank">PDB</a> entry <a rel="nofollow" class="external text" href="http://www.rcsb.org/pdb/cgi/explore.cgi?pdbId=1PFQ">1PFQ</a>.