The Cysteine Proteases - I
A family of cysteine proteases (also called thiol proteases) is widely distributed in fruits:
- Papain (papaya), ficin (figs), bromelain (pineapple), and actinidin (kiwi) are structurally very similar to the serine proteases.
- All have a cysteine and a histidine at the catalytic site
- In papain, the catalytic residues are Cys25, His159, and Asn175
- Actinidin has Cys25, His162, and Asn182
- Some workers question whether the Asn actually have any function
- The backbones align with an rmsd of 0.72 A:
- Residue identity is 47%; similarity is 58%
Here are the catalytic sites:
| Actinidin (2act) |
Catalytic Site |
 |
 |
| Papain (9pap) |
Catalytic Site |
 |
 |
With all this similarity to the catalytic site of the serine proteases, we might expect a very similar mechanism. And that's what we get.
This page last modified 1:14 PM on Thursday March 17th, 2011.
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