TIM Barrel

"In molecular biology the TIM barrel is a conserved protein fold consisting of eight ?-helices and eight parallel ?-strands that alternate along the peptide backbone. The structure is named after triosephosphate isomerase, a conserved metabolic enzyme. TIM barrels are one of the most common protein folds."
http://en.wikipedia.org/wiki/TIM_barrel

Model of based on the Protein Data Bank entry 1TIM:
http://www.rcsb.org/pdb/explore/explore.do?structureId=1tim
(Triose phosphate isomerase from chicken muscle.)

STL file created using VMD:
http://www.ks.uiuc.edu/Research/vmd/