Molecule of the Month: Concanavalin A and Circular Permutation
For some proteins, clipped and reassembled sequences can produce the same 3D shape
Circular Permutation Discovered
Exploring the Structure
Circularly Permuted Glucanase (PDB entries 2ayh, 1ajk, 1ajo and 1cpm)
Scientists are also great tinkerers. As soon as they discovered the process of circular permutation, they had to try it out themselves. The glucanase protein shown here (PDB entries 2ayh , 1ajk , 1ajo and 1cpm ) has been permuted in several different ways, by cutting the gene in different places and reassembling the two pieces. In this picture, each protein chain is colored blue at one end, red at the other, and rainbow colors in between. Notice that the overall protein fold is the same in each one, except that the ends are in a different place. This demonstrates that protein folding is a robust process, and that the protein fold is determined by the sequence, even if it's shuffled around a bit. You can explore these structures in more detail by clicking on the image for an interactive JSmol.
Topics for Further Discussion
- Can you find other examples of circularly-permuted proteins in the PDB?
- Can you think of any ways that circular permutation would improve the function of a protein?
April 2010, David Goodsellhttp://doi.org/10.2210/rcsb_pdb/mom_2010_4