Investigating the Mechanism of 
Carboxypeptidase A

This is an interactive view of an enzyme called "carboxypeptidase A."  Carboxypeptidase A is a protease that cleaves peptide bonds at the C-terminal residues of polypeptide substrates.  If you highlight the active site and zoom in, you can see a hydrophobic pocket that is ideally suited to binding bulky hydrophobic side chains. This conveys the selectivity of the enzyme for peptides with C-terminal bulky, hydrophobic residues.

        In this view, only the backbone of the carboxypeptidase A chain is shown. There is a zinc ion that is required for catalysis. The zinc is bound to his 69, his 196 and glu 72 at the enzyme active site.
 
 
Zoom in on the active site.
Highlight zinc.
Highlight his 69.
Highlight his 196.
Highlight glu 72.
The zinc ion interacts with the substrate to make the peptide bond easier to break. There is also a positively-charged arg residue at the active site. This binds to the negatively-charged carboxylic acid group of the substrate residue that will be cleaved. The substrate in this model is a gly-tyr dipeptide.
Highlight the substrate.
Highlight arg 145.
This model was created using the coordinates from the pdb file 3CPA by W.N.Lipscomb, 1982.

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Cindy Klevickis
klevicca@jmu.edu