File:TIM-end ribbon shaded.png

English: Shaded, black&white ribbon drawing of the 3-dimensional structure of the enzyme triose phosphate isomerase, the prototypical example of the "TIM barrel" protein fold. It has a central, twisted cylinder of 8 parallel beta strands, surrounded by a cylinder of alpha-helices. Arrowheads show the N- to C-terminal direction of the chains, which wind around the barrel counter-clockwise from the bottom, in right-handed crossover connections from one beta strand to the next. The enzyme active site is at the end of the barrel toward you, and the active molecule is a dimer of two identical chains. Hand drawn by Jane S. Richardson from PDB file 1tim.