This is the human enzyme DPP-4. Well, DPP-4 chewing on GLP-1 hormone. When you eat, cells in your intestine releases incretin hormones like GLP-1. GLP-1 stimulates the release of insulin from your pancreas and hinders the release of glucagon (which has the opposite effect of insulin, increasing the concentration of glucose in the blood). The incretins make sure that your blood glucose level is well regulated, however it is important that incretins like GLP-1 does not have a too long effect. This is where DPP-4 comes into play. DPP-4 is an amazingly beautiful enzyme on the surface of almost every cell in the human body. Deep inside this hollow peptidase, is the active site. GLP-1 can access the heart of DPP-4 through a perfect opening and when it does, exactly two amino acids are cleaved off the hormone, rendering it totally inactive.

Included in the source files, you'll find the DPP-4 enzyme, the GLP-1 hormone and a split copy of DPP-4. Print it out and marvel at the beauty of nature and science.

I work at the worlds largest producer of diabetes related drugs and in my team I'm responsible for an upcoming drug, that inhibits the effect of DPP-4 thereby increasing the effect of incretins. This drug will help MILLIONS of type-2 diabetes patients world wide. This structure is sitting next to my human insulin model on my desk.

Monomer isolated from 2RGU pdb model.

DPP-4 (complete structure)
Supports are required and when I printed this with 0.3mm layer height, it took me 16h30m. The complete model requires a lot of postprint cleaning and the hollow structure is hard to clean out properly.

DPP-4 (split model)
The split model requires supports and will have to be glued together. It is much easier to clean out post printing, but you'll have to make due with a glued seam. However, the split model i way faster to print than the complete model.
Hmm I'm having problems making the two halves fitting together. I can't see any problem with the model, so it might be my print. Consider yourselves warned ;)

GLP-1
This is a tiny model, but still requires supports. Theses are easily removed and due to the tiny structure, you can print it with 0.1mm layer height and be done quickly.

General remarks
I've printed the complete DPP-4 structure with a 0.3 mm layer height and with supports with 2 interface layers. My models were sliced in Slic3r and printed in PLA on my Reprappro Mendel Mono.