Evolution of Protein Structures
Part III
Part III. Enzymes with the Same 3-D Shape but Different Functions
Another class of proteins/enzymes is where enzymes with completely different Function have the same 3-D shape. 17 different enzymes catalyzing 17 different reactions have the beta-barrel 3-D shape.
Figure 12. The beta-barrel structure prototype for at least 21 enzymes and proteins.
Figure from unknown source who owns the copyright.
These enzymes have no similarity in AA sequence so that different amino acids are important in folding the backbone of the protein/enzyme to form the beta-barrel.
Figure 13. Beta-barrel enzyme (triose-P isomerase). The top view (on the left) looking down on to beta-barrel (count the 8 beta strands) and side view (on the right) are shown for triose-P isomerase.
Figure from Voet/Biochemsitry -- copyright 1990 John Wiley & Sons
The general conclusion is that the beta-barrel 3-D shape must be a very good one for making enzymes since so many are found to use it. Since the substrates can sit down in the saddle of the barrel, it seems like it makes a good 3-D binding site for an enzyme.
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©Wilbur H. Campbell, 1995; wcampbel@mtu.edu